crypto/x86: Use XORL r32,32 in curve25519-x86_64.c

PATCH In review Uros Bizjak 5 participants 11 messages Aug 27, 2020 – Sep 11, 2020

Subsystems (2)

x86 Crypto API

lore

Share & tools

lore

Uros Bizjak

author

2020-08-27 17:31 UTC #0 lore raw

PATCH 1/1 crypto/x86: Use XORL r32,32 in curve25519-x86_64.c

x86_64 zero extends 32bit operations, so for 64bit operands, XORL r32,r32 is functionally equal to XORL r64,r64, but avoids a REX prefix byte when legacy registers are used.

Signed-off-by Uros Bizjak <[email protected]>

Cc Herbert Xu <[email protected]>

Cc "David S. Miller" <[email protected]>

---
 arch/x86/crypto/curve25519-x86_64.c | 68 ++++++++++++++---------------
 1 file changed, 34 insertions(+), 34 deletions(-)

arch/x86/crypto/curve25519-x86_64.c +34 ~~-34~~

index 8acbb6584a37..a9edb6f8a0ba 100644
@@ -45,11 +45,11 @@ static inline u64 add_scalar(u64 *out, const u64 *f1, u64 f2)
 
 	asm volatile(
 		/* Clear registers to propagate the carry bit */
-		"  xor %%r8, %%r8;"
-		"  xor %%r9, %%r9;"
-		"  xor %%r10, %%r10;"
-		"  xor %%r11, %%r11;"
-		"  xor %1, %1;"
+		"  xor %%r8d, %%r8d;"
+		"  xor %%r9d, %%r9d;"
+		"  xor %%r10d, %%r10d;"
+		"  xor %%r11d, %%r11d;"
+		"  xor %k1, %k1;"
 
 		/* Begin addition chain */
 		"  addq 0(%3), %0;"

@@ -93,7 +93,7 @@ static inline void fadd(u64 *out, const u64 *f1, const u64 *f2)
 		"  cmovc %0, %%rax;"
 
 		/* Step 2: Add carry*38 to the original sum */
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  add %%rax, %%r8;"
 		"  adcx %%rcx, %%r9;"
 		"  movq %%r9, 8(%1);"

@@ -165,28 +165,28 @@ static inline void fmul(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
 		/* Compute src1[0] * src2 */
 		"  movq 0(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 0(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  movq %%r8, 0(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 8(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"
 		/* Compute src1[1] * src2 */
 		"  movq 8(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 16(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[2] * src2 */
 		"  movq 16(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 16(%0), %%r8;"    "  movq %%r8, 16(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 16(%0), %%r8;"   "  movq %%r8, 16(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 24(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[3] * src2 */
 		"  movq 24(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 24(%0), %%r8;"    "  movq %%r8, 24(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 24(%0), %%r8;"   "  movq %%r8, 24(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 32(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 40(%0);"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 48(%0);"    "  mov $0, %%rax;"

@@ -200,7 +200,7 @@ static inline void fmul(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %3, %3;"
+		"  xor %k3, %k3;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -246,28 +246,28 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
 		/* Compute src1[0] * src2 */
 		"  movq 0(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 0(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  movq %%r8, 0(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 8(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"
 		/* Compute src1[1] * src2 */
 		"  movq 8(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 16(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[2] * src2 */
 		"  movq 16(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 16(%0), %%r8;"    "  movq %%r8, 16(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 16(%0), %%r8;"   "  movq %%r8, 16(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 24(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[3] * src2 */
 		"  movq 24(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 24(%0), %%r8;"    "  movq %%r8, 24(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 24(%0), %%r8;"   "  movq %%r8, 24(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 32(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 40(%0);"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 48(%0);"    "  mov $0, %%rax;"

@@ -277,29 +277,29 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
 		/* Compute src1[0] * src2 */
 		"  movq 32(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 64(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 72(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  movq %%r8, 64(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  movq %%r10, 72(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"
 		/* Compute src1[1] * src2 */
 		"  movq 40(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 72(%0), %%r8;"    "  movq %%r8, 72(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 80(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 72(%0), %%r8;"   "  movq %%r8, 72(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 80(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[2] * src2 */
 		"  movq 48(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 80(%0), %%r8;"    "  movq %%r8, 80(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 88(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 80(%0), %%r8;"   "  movq %%r8, 80(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 88(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[3] * src2 */
 		"  movq 56(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 88(%0), %%r8;"    "  movq %%r8, 88(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 96(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 88(%0), %%r8;"   "  movq %%r8, 88(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 96(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 104(%0);"    "  mov $0, %%r8;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 112(%0);"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"     "  movq %%rax, 120(%0);"

@@ -312,7 +312,7 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %3, %3;"
+		"  xor %k3, %k3;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -345,7 +345,7 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 96(%1), %%r8, %%r13;"
-		"  xor %3, %3;"
+		"  xor %k3, %k3;"
 		"  adoxq 64(%1), %%r8;"
 		"  mulxq 104(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -516,7 +516,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 
 		/* Step 1: Compute all partial products */
 		"  movq 0(%1), %%rdx;"                                       /* f[0] */
-		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
 		"  mulxq 16(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
 		"  mulxq 24(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
 		"  movq 24(%1), %%rdx;"                                      /* f[3] */

@@ -526,7 +526,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 		"  mulxq 16(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
 		/* Step 2: Compute two parallel carry chains */
-		"  xor %%r15, %%r15;"
+		"  xor %%r15d, %%r15d;"
 		"  adox %%rax, %%r10;"
 		"  adcx %%r8, %%r8;"
 		"  adox %%rcx, %%r11;"

@@ -563,7 +563,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -607,7 +607,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 	asm volatile(
 		/* Step 1: Compute all partial products */
 		"  movq 0(%1), %%rdx;"                                       /* f[0] */
-		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
 		"  mulxq 16(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
 		"  mulxq 24(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
 		"  movq 24(%1), %%rdx;"                                      /* f[3] */

@@ -617,7 +617,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		"  mulxq 16(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
 		/* Step 2: Compute two parallel carry chains */
-		"  xor %%r15, %%r15;"
+		"  xor %%r15d, %%r15d;"
 		"  adox %%rax, %%r10;"
 		"  adcx %%r8, %%r8;"
 		"  adox %%rcx, %%r11;"

@@ -647,7 +647,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 
 		/* Step 1: Compute all partial products */
 		"  movq 32(%1), %%rdx;"                                       /* f[0] */
-		"  mulxq 40(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+		"  mulxq 40(%1), %%r8, %%r14;"     "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
 		"  mulxq 48(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
 		"  mulxq 56(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
 		"  movq 56(%1), %%rdx;"                                      /* f[3] */

@@ -657,7 +657,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		"  mulxq 48(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
 		/* Step 2: Compute two parallel carry chains */
-		"  xor %%r15, %%r15;"
+		"  xor %%r15d, %%r15d;"
 		"  adox %%rax, %%r10;"
 		"  adcx %%r8, %%r8;"
 		"  adox %%rcx, %%r11;"

@@ -692,7 +692,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -725,7 +725,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 96(%1), %%r8, %%r13;"
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  adoxq 64(%1), %%r8;"
 		"  mulxq 104(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

Signature · 1 line

2.26.2

Jason A. Donenfeld

2020-09-01 18:13 UTC #2 lore raw

Hi Uros,

Thanks for this patch. This seems correct to me, since indeed those clear the top bits anyway, and having smaller code seems good. But first -- I'm wondering -- have you stuck this into Vale/Hacl to see if it still checks out there? I'm CC'ing Karthik/Aymeric/Chris/Jonathan who might be interested in taking a look at that. Seems like it might be easy to just special case this in Xor64 for the case where the operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.

Jason

Quoted 261 lines · Ard Biesheuvel

(+ Jason)

Quoted 257 lines · Uros Bizjak

x86_64 zero extends 32bit operations, so for 64bit operands, XORL r32,r32 is functionally equal to XORL r64,r64, but avoids a REX prefix byte when legacy registers are used.

Signed-off-by Uros Bizjak <[email protected]>

Cc Herbert Xu <[email protected]>

Cc "David S. Miller" <[email protected]>

---
 arch/x86/crypto/curve25519-x86_64.c | 68 ++++++++++++++---------------
 1 file changed, 34 insertions(+), 34 deletions(-)

arch/x86/crypto/curve25519-x86_64.c +34 ~~-35~~

index 8acbb6584a37..a9edb6f8a0ba 100644
@@ -45,11 +45,11 @@ static inline u64 add_scalar(u64 *out, const u64 *f1, u64 f2)
 
        asm volatile(
                /* Clear registers to propagate the carry bit */
-               "  xor %%r8, %%r8;"
-               "  xor %%r9, %%r9;"
-               "  xor %%r10, %%r10;"
-               "  xor %%r11, %%r11;"
-               "  xor %1, %1;"
+               "  xor %%r8d, %%r8d;"
+               "  xor %%r9d, %%r9d;"
+               "  xor %%r10d, %%r10d;"
+               "  xor %%r11d, %%r11d;"
+               "  xor %k1, %k1;"
 
                /* Begin addition chain */
                "  addq 0(%3), %0;"

@@ -93,7 +93,7 @@ static inline void fadd(u64 *out, const u64 *f1, const u64 *f2)
                "  cmovc %0, %%rax;"
 
                /* Step 2: Add carry*38 to the original sum */
-               "  xor %%rcx, %%rcx;"
+               "  xor %%ecx, %%ecx;"
                "  add %%rax, %%r8;"
                "  adcx %%rcx, %%r9;"
                "  movq %%r9, 8(%1);"

@@ -165,28 +165,28 @@ static inline void fmul(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
                /* Compute src1[0] * src2 */
                "  movq 0(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 0(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  movq %%r8, 0(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 8(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"
                /* Compute src1[1] * src2 */
                "  movq 8(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 16(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
                /* Compute src1[2] * src2 */
                "  movq 16(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 16(%0), %%r8;"    "  movq %%r8, 16(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 16(%0), %%r8;"   "  movq %%r8, 16(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 24(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
                /* Compute src1[3] * src2 */
                "  movq 24(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 24(%0), %%r8;"    "  movq %%r8, 24(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 24(%0), %%r8;"   "  movq %%r8, 24(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 32(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 40(%0);"    "  mov $0, %%r8;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 48(%0);"    "  mov $0, %%rax;"

@@ -200,7 +200,7 @@ static inline void fmul(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
                /* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
                "  mov $38, %%rdx;"
                "  mulxq 32(%1), %%r8, %%r13;"
-               "  xor %3, %3;"
+               "  xor %k3, %k3;"
                "  adoxq 0(%1), %%r8;"
                "  mulxq 40(%1), %%r9, %%rbx;"
                "  adcx %%r13, %%r9;"

@@ -246,28 +246,28 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
                /* Compute src1[0] * src2 */
                "  movq 0(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 0(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  movq %%r8, 0(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 8(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"
                /* Compute src1[1] * src2 */
                "  movq 8(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 16(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
                /* Compute src1[2] * src2 */
                "  movq 16(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 16(%0), %%r8;"    "  movq %%r8, 16(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 16(%0), %%r8;"   "  movq %%r8, 16(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 24(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
                /* Compute src1[3] * src2 */
                "  movq 24(%1), %%rdx;"
-               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 24(%0), %%r8;"    "  movq %%r8, 24(%0);"
+               "  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 24(%0), %%r8;"   "  movq %%r8, 24(%0);"
                "  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 32(%0);"
                "  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 40(%0);"    "  mov $0, %%r8;"
                "  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 48(%0);"    "  mov $0, %%rax;"

@@ -277,29 +277,29 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
                /* Compute src1[0] * src2 */
                "  movq 32(%1), %%rdx;"
-               "  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 64(%0);"
-               "  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 72(%0);"
+               "  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  movq %%r8, 64(%0);"
+               "  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  movq %%r10, 72(%0);"
                "  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
                "  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"
                /* Compute src1[1] * src2 */
                "  movq 40(%1), %%rdx;"
-               "  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 72(%0), %%r8;"    "  movq %%r8, 72(%0);"
-               "  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 80(%0);"
+               "  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 72(%0), %%r8;"   "  movq %%r8, 72(%0);"
+               "  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 80(%0);"
                "  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
                "  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
                /* Compute src1[2] * src2 */
                "  movq 48(%1), %%rdx;"
-               "  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 80(%0), %%r8;"    "  movq %%r8, 80(%0);"
-               "  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 88(%0);"
+               "  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 80(%0), %%r8;"   "  movq %%r8, 80(%0);"
+               "  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 88(%0);"
                "  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
                "  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
                /* Compute src1[3] * src2 */
                "  movq 56(%1), %%rdx;"
-               "  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 88(%0), %%r8;"    "  movq %%r8, 88(%0);"
-               "  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 96(%0);"
+               "  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 88(%0), %%r8;"   "  movq %%r8, 88(%0);"
+               "  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 96(%0);"
                "  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 104(%0);"    "  mov $0, %%r8;"
                "  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 112(%0);"    "  mov $0, %%rax;"
                                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"     "  movq %%rax, 120(%0);"

@@ -312,7 +312,7 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
                /* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
                "  mov $38, %%rdx;"
                "  mulxq 32(%1), %%r8, %%r13;"
-               "  xor %3, %3;"
+               "  xor %k3, %k3;"
                "  adoxq 0(%1), %%r8;"
                "  mulxq 40(%1), %%r9, %%rbx;"
                "  adcx %%r13, %%r9;"

@@ -345,7 +345,7 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
                /* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
                "  mov $38, %%rdx;"
                "  mulxq 96(%1), %%r8, %%r13;"
-               "  xor %3, %3;"
+               "  xor %k3, %k3;"
                "  adoxq 64(%1), %%r8;"
                "  mulxq 104(%1), %%r9, %%rbx;"
                "  adcx %%r13, %%r9;"

@@ -516,7 +516,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 
                /* Step 1: Compute all partial products */
                "  movq 0(%1), %%rdx;"                                       /* f[0] */
-               "  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+               "  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
                "  mulxq 16(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
                "  mulxq 24(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
                "  movq 24(%1), %%rdx;"                                      /* f[3] */

@@ -526,7 +526,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
                "  mulxq 16(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
                /* Step 2: Compute two parallel carry chains */
-               "  xor %%r15, %%r15;"
+               "  xor %%r15d, %%r15d;"
                "  adox %%rax, %%r10;"
                "  adcx %%r8, %%r8;"
                "  adox %%rcx, %%r11;"

@@ -563,7 +563,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
                /* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
                "  mov $38, %%rdx;"
                "  mulxq 32(%1), %%r8, %%r13;"
-               "  xor %%rcx, %%rcx;"
+               "  xor %%ecx, %%ecx;"
                "  adoxq 0(%1), %%r8;"
                "  mulxq 40(%1), %%r9, %%rbx;"
                "  adcx %%r13, %%r9;"

@@ -607,7 +607,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
        asm volatile(
                /* Step 1: Compute all partial products */
                "  movq 0(%1), %%rdx;"                                       /* f[0] */
-               "  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+               "  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
                "  mulxq 16(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
                "  mulxq 24(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
                "  movq 24(%1), %%rdx;"                                      /* f[3] */

@@ -617,7 +617,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
                "  mulxq 16(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
                /* Step 2: Compute two parallel carry chains */
-               "  xor %%r15, %%r15;"
+               "  xor %%r15d, %%r15d;"
                "  adox %%rax, %%r10;"
                "  adcx %%r8, %%r8;"
                "  adox %%rcx, %%r11;"

@@ -647,7 +647,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 
                /* Step 1: Compute all partial products */
                "  movq 32(%1), %%rdx;"                                       /* f[0] */
-               "  mulxq 40(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+               "  mulxq 40(%1), %%r8, %%r14;"     "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
                "  mulxq 48(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
                "  mulxq 56(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
                "  movq 56(%1), %%rdx;"                                      /* f[3] */

@@ -657,7 +657,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
                "  mulxq 48(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
                /* Step 2: Compute two parallel carry chains */
-               "  xor %%r15, %%r15;"
+               "  xor %%r15d, %%r15d;"
                "  adox %%rax, %%r10;"
                "  adcx %%r8, %%r8;"
                "  adox %%rcx, %%r11;"

@@ -692,7 +692,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
                /* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
                "  mov $38, %%rdx;"
                "  mulxq 32(%1), %%r8, %%r13;"
-               "  xor %%rcx, %%rcx;"
+               "  xor %%ecx, %%ecx;"
                "  adoxq 0(%1), %%r8;"
                "  mulxq 40(%1), %%r9, %%rbx;"
                "  adcx %%r13, %%r9;"

@@ -725,7 +725,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
                /* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
                "  mov $38, %%rdx;"
                "  mulxq 96(%1), %%r8, %%r13;"
-               "  xor %%rcx, %%rcx;"
+               "  xor %%ecx, %%ecx;"
                "  adoxq 64(%1), %%r8;"
                "  mulxq 104(%1), %%r9, %%rbx;"
                "  adcx %%r13, %%r9;"
--

2.26.2

Jason A. Donenfeld

2020-09-01 19:12 UTC #3 lore raw

Quoted 3 lines · Jason A. Donenfeld

operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.

On a Skylake server (Xeon Gold 5120), I'm unable to see any measurable difference with this, at all, no matter how much I median or mean or reduce noise by disabling interrupts.

One thing that sticks out is that all the replacements of r8-r15 by their %r8d-r15d counterparts still have the REX prefix, as is necessary to access those registers. The only ones worth changing, then, are the legacy registers, and on a whole, this amounts to only 48 bytes of difference.

Uros Bizjak

author

2020-09-02 05:50 UTC #4 lore raw

Quoted 10 lines · Jason A. Donenfeld

Quoted 3 lines · Jason A. Donenfeld
operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.
On a Skylake server (Xeon Gold 5120), I'm unable to see any measurable difference with this, at all, no matter how much I median or mean or reduce noise by disabling interrupts.

Quoted 5 lines

One thing that sticks out is that all the replacements of r8-r15 by their %r8d-r15d counterparts still have the REX prefix, as is necessary to access those registers. The only ones worth changing, then, are the legacy registers, and on a whole, this amounts to only 48 bytes of difference.

The patch implements one of x86 target specific optimizations, performed by gcc. The optimization results in code size savings of one byte, where REX prefix is omitted with legacy registers, but otherwise should have no measurable runtime effect. Since gcc applies this optimization universally to all integer registers, I took the same approach and implemented the same change to legacy and REX registers. As measured above, 48 bytes saved is a good result for such a trivial optimization.

Uros.

[email protected]

2020-09-02 09:17 UTC #5 lore raw

Quoted 17 lines · Uros Bizjak

Quoted 10 lines · Jason A. Donenfeld
Quoted 3 lines · Jason A. Donenfeld
operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.
On a Skylake server (Xeon Gold 5120), I'm unable to see any measurable difference with this, at all, no matter how much I median or mean or reduce noise by disabling interrupts.
Quoted 5 lines
One thing that sticks out is that all the replacements of r8-r15 by their %r8d-r15d counterparts still have the REX prefix, as is necessary to access those registers. The only ones worth changing, then, are the legacy registers, and on a whole, this amounts to only 48 bytes of difference.

Quoted 8 lines

The patch implements one of x86 target specific optimizations, performed by gcc. The optimization results in code size savings of one byte, where REX prefix is omitted with legacy registers, but otherwise should have no measurable runtime effect. Since gcc applies this optimization universally to all integer registers, I took the same approach and implemented the same change to legacy and REX registers. As measured above, 48 bytes saved is a good result for such a trivial optimization.

Could we instead implement this optimization in GAS ? Then we can leave the code as-is.

Uros Bizjak

author

2020-09-02 11:36 UTC #6 lore raw

Quoted 28 lines · On Wed, Sep 2, 2020 at 11:17 AM <[email protected]> wrote:

Quoted 17 lines · Uros Bizjak
Quoted 10 lines · Jason A. Donenfeld
Quoted 3 lines · Jason A. Donenfeld
operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.
On a Skylake server (Xeon Gold 5120), I'm unable to see any measurable difference with this, at all, no matter how much I median or mean or reduce noise by disabling interrupts.
Quoted 5 lines
One thing that sticks out is that all the replacements of r8-r15 by their %r8d-r15d counterparts still have the REX prefix, as is necessary to access those registers. The only ones worth changing, then, are the legacy registers, and on a whole, this amounts to only 48 bytes of difference.
Quoted 8 lines
The patch implements one of x86 target specific optimizations, performed by gcc. The optimization results in code size savings of one byte, where REX prefix is omitted with legacy registers, but otherwise should have no measurable runtime effect. Since gcc applies this optimization universally to all integer registers, I took the same approach and implemented the same change to legacy and REX registers. As measured above, 48 bytes saved is a good result for such a trivial optimization.

Quoted 2 lines

Could we instead implement this optimization in GAS ? Then we can leave the code as-is.

I don't think that e.g. "xorq %rax,%rax" should universally be translated to "xorl %eax,%eax" in the assembler. Perhaps the author expected exactly 3 bytes (to align the code or similar), and the assembler would change the length to 2 bytes behind his back, breaking the expectations.

Uros.

Jason A. Donenfeld

2020-09-02 15:00 UTC #7 lore raw

Quoted 30 lines · Uros Bizjak

Quoted 28 lines · On Wed, Sep 2, 2020 at 11:17 AM <[email protected]> wrote:
Quoted 25 lines · Uros Bizjak
Quoted 10 lines · Jason A. Donenfeld
Quoted 3 lines · Jason A. Donenfeld
operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.
On a Skylake server (Xeon Gold 5120), I'm unable to see any measurable difference with this, at all, no matter how much I median or mean or reduce noise by disabling interrupts.
Quoted 5 lines
One thing that sticks out is that all the replacements of r8-r15 by their %r8d-r15d counterparts still have the REX prefix, as is necessary to access those registers. The only ones worth changing, then, are the legacy registers, and on a whole, this amounts to only 48 bytes of difference.
The patch implements one of x86 target specific optimizations, performed by gcc. The optimization results in code size savings of one byte, where REX prefix is omitted with legacy registers, but otherwise should have no measurable runtime effect. Since gcc applies this optimization universally to all integer registers, I took the same approach and implemented the same change to legacy and REX registers. As measured above, 48 bytes saved is a good result for such a trivial optimization.

Quoted 8 lines

Quoted 2 lines
Could we instead implement this optimization in GAS ? Then we can leave the code as-is.
I don't think that e.g. "xorq %rax,%rax" should universally be translated to "xorl %eax,%eax" in the assembler. Perhaps the author expected exactly 3 bytes (to align the code or similar), and the assembler would change the length to 2 bytes behind his back, breaking the expectations.

Are you sure that's something that GAS actually provides now? Seems like a lot of mnemonics have ambiguous/injective encodings, and this wouldn't make things any different. Most authors use .byte or .align when they care about the actual bytes, no?

Jason A. Donenfeld

2020-09-02 14:58 UTC #8 lore raw

In reply to [email protected]

Quoted 28 lines · On Wed, Sep 2, 2020 at 11:44 AM <[email protected]> wrote:

Quoted 17 lines · Uros Bizjak
Quoted 10 lines · Jason A. Donenfeld
Quoted 3 lines · Jason A. Donenfeld
operands are the same. Also, have you seen any measurable differences when benching this? I can stick it into kbench9000 to see if you haven't looked yet.
On a Skylake server (Xeon Gold 5120), I'm unable to see any measurable difference with this, at all, no matter how much I median or mean or reduce noise by disabling interrupts.
Quoted 5 lines
One thing that sticks out is that all the replacements of r8-r15 by their %r8d-r15d counterparts still have the REX prefix, as is necessary to access those registers. The only ones worth changing, then, are the legacy registers, and on a whole, this amounts to only 48 bytes of difference.
Quoted 8 lines
The patch implements one of x86 target specific optimizations, performed by gcc. The optimization results in code size savings of one byte, where REX prefix is omitted with legacy registers, but otherwise should have no measurable runtime effect. Since gcc applies this optimization universally to all integer registers, I took the same approach and implemented the same change to legacy and REX registers. As measured above, 48 bytes saved is a good result for such a trivial optimization.

Quoted 2 lines

Could we instead implement this optimization in GAS ? Then we can leave the code as-is.

I rather like that idea. Though I wonder if some would balk at it for smelling a bit like the MIPS assembler with its optimization pass...

Jason A. Donenfeld

Acked-by on v1 1/1

2020-09-07 17:46 UTC #9 lore raw

In reply to Uros Bizjak

Hi Uros, Herbert,

Quoted 256 lines · Uros Bizjak

x86_64 zero extends 32bit operations, so for 64bit operands, XORL r32,r32 is functionally equal to XORL r64,r64, but avoids a REX prefix byte when legacy registers are used.

Signed-off-by Uros Bizjak <[email protected]>

Cc Herbert Xu <[email protected]>

Cc "David S. Miller" <[email protected]>

---
 arch/x86/crypto/curve25519-x86_64.c | 68 ++++++++++++++---------------
 1 file changed, 34 insertions(+), 34 deletions(-)

arch/x86/crypto/curve25519-x86_64.c +34 ~~-34~~

index 8acbb6584a37..a9edb6f8a0ba 100644
@@ -45,11 +45,11 @@ static inline u64 add_scalar(u64 *out, const u64 *f1, u64 f2)
 
 	asm volatile(
 		/* Clear registers to propagate the carry bit */
-		"  xor %%r8, %%r8;"
-		"  xor %%r9, %%r9;"
-		"  xor %%r10, %%r10;"
-		"  xor %%r11, %%r11;"
-		"  xor %1, %1;"
+		"  xor %%r8d, %%r8d;"
+		"  xor %%r9d, %%r9d;"
+		"  xor %%r10d, %%r10d;"
+		"  xor %%r11d, %%r11d;"
+		"  xor %k1, %k1;"
 
 		/* Begin addition chain */
 		"  addq 0(%3), %0;"

@@ -93,7 +93,7 @@ static inline void fadd(u64 *out, const u64 *f1, const u64 *f2)
 		"  cmovc %0, %%rax;"
 
 		/* Step 2: Add carry*38 to the original sum */
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  add %%rax, %%r8;"
 		"  adcx %%rcx, %%r9;"
 		"  movq %%r9, 8(%1);"

@@ -165,28 +165,28 @@ static inline void fmul(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
 		/* Compute src1[0] * src2 */
 		"  movq 0(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 0(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  movq %%r8, 0(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 8(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"
 		/* Compute src1[1] * src2 */
 		"  movq 8(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 16(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[2] * src2 */
 		"  movq 16(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 16(%0), %%r8;"    "  movq %%r8, 16(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 16(%0), %%r8;"   "  movq %%r8, 16(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 24(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[3] * src2 */
 		"  movq 24(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 24(%0), %%r8;"    "  movq %%r8, 24(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 24(%0), %%r8;"   "  movq %%r8, 24(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 32(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 40(%0);"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 48(%0);"    "  mov $0, %%rax;"

@@ -200,7 +200,7 @@ static inline void fmul(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %3, %3;"
+		"  xor %k3, %k3;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -246,28 +246,28 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
 		/* Compute src1[0] * src2 */
 		"  movq 0(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 0(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  movq %%r8, 0(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 8(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"
 		/* Compute src1[1] * src2 */
 		"  movq 8(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 8(%0), %%r8;"    "  movq %%r8, 8(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 16(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[2] * src2 */
 		"  movq 16(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 16(%0), %%r8;"    "  movq %%r8, 16(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 16(%0), %%r8;"   "  movq %%r8, 16(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 24(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[3] * src2 */
 		"  movq 24(%1), %%rdx;"
-		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 24(%0), %%r8;"    "  movq %%r8, 24(%0);"
+		"  mulxq 0(%3), %%r8, %%r9;"       "  xor %%r10d, %%r10d;"   "  adcxq 24(%0), %%r8;"   "  movq %%r8, 24(%0);"
 		"  mulxq 8(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 32(%0);"
 		"  mulxq 16(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 40(%0);"    "  mov $0, %%r8;"
 		"  mulxq 24(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 48(%0);"    "  mov $0, %%rax;"

@@ -277,29 +277,29 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 
 		/* Compute src1[0] * src2 */
 		"  movq 32(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  movq %%r8, 64(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  movq %%r10, 72(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  movq %%r8, 64(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  movq %%r10, 72(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"
 		/* Compute src1[1] * src2 */
 		"  movq 40(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"     "  adcxq 72(%0), %%r8;"    "  movq %%r8, 72(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 80(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 72(%0), %%r8;"   "  movq %%r8, 72(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 80(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[2] * src2 */
 		"  movq 48(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 80(%0), %%r8;"    "  movq %%r8, 80(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 88(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 80(%0), %%r8;"   "  movq %%r8, 80(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 88(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  mov $0, %%r8;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"
 		/* Compute src1[3] * src2 */
 		"  movq 56(%1), %%rdx;"
-		"  mulxq 32(%3), %%r8, %%r9;"       "  xor %%r10, %%r10;"    "  adcxq 88(%0), %%r8;"    "  movq %%r8, 88(%0);"
-		"  mulxq 40(%3), %%r10, %%r11;"     "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 96(%0);"
+		"  mulxq 32(%3), %%r8, %%r9;"      "  xor %%r10d, %%r10d;"   "  adcxq 88(%0), %%r8;"   "  movq %%r8, 88(%0);"
+		"  mulxq 40(%3), %%r10, %%r11;"    "  adox %%r9, %%r10;"     "  adcx %%rbx, %%r10;"    "  movq %%r10, 96(%0);"
 		"  mulxq 48(%3), %%rbx, %%r13;"    "  adox %%r11, %%rbx;"    "  adcx %%r14, %%rbx;"    "  movq %%rbx, 104(%0);"    "  mov $0, %%r8;"
 		"  mulxq 56(%3), %%r14, %%rdx;"    "  adox %%r13, %%r14;"    "  adcx %%rax, %%r14;"    "  movq %%r14, 112(%0);"    "  mov $0, %%rax;"
 		                                   "  adox %%rdx, %%rax;"    "  adcx %%r8, %%rax;"     "  movq %%rax, 120(%0);"

@@ -312,7 +312,7 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %3, %3;"
+		"  xor %k3, %k3;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -345,7 +345,7 @@ static inline void fmul2(u64 *out, const u64 *f1, const u64 *f2, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 96(%1), %%r8, %%r13;"
-		"  xor %3, %3;"
+		"  xor %k3, %k3;"
 		"  adoxq 64(%1), %%r8;"
 		"  mulxq 104(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -516,7 +516,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 
 		/* Step 1: Compute all partial products */
 		"  movq 0(%1), %%rdx;"                                       /* f[0] */
-		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
 		"  mulxq 16(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
 		"  mulxq 24(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
 		"  movq 24(%1), %%rdx;"                                      /* f[3] */

@@ -526,7 +526,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 		"  mulxq 16(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
 		/* Step 2: Compute two parallel carry chains */
-		"  xor %%r15, %%r15;"
+		"  xor %%r15d, %%r15d;"
 		"  adox %%rax, %%r10;"
 		"  adcx %%r8, %%r8;"
 		"  adox %%rcx, %%r11;"

@@ -563,7 +563,7 @@ static inline void fsqr(u64 *out, const u64 *f, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -607,7 +607,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 	asm volatile(
 		/* Step 1: Compute all partial products */
 		"  movq 0(%1), %%rdx;"                                       /* f[0] */
-		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+		"  mulxq 8(%1), %%r8, %%r14;"      "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
 		"  mulxq 16(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
 		"  mulxq 24(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
 		"  movq 24(%1), %%rdx;"                                      /* f[3] */

@@ -617,7 +617,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		"  mulxq 16(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
 		/* Step 2: Compute two parallel carry chains */
-		"  xor %%r15, %%r15;"
+		"  xor %%r15d, %%r15d;"
 		"  adox %%rax, %%r10;"
 		"  adcx %%r8, %%r8;"
 		"  adox %%rcx, %%r11;"

@@ -647,7 +647,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 
 		/* Step 1: Compute all partial products */
 		"  movq 32(%1), %%rdx;"                                       /* f[0] */
-		"  mulxq 40(%1), %%r8, %%r14;"      "  xor %%r15, %%r15;"     /* f[1]*f[0] */
+		"  mulxq 40(%1), %%r8, %%r14;"     "  xor %%r15d, %%r15d;"   /* f[1]*f[0] */
 		"  mulxq 48(%1), %%r9, %%r10;"     "  adcx %%r14, %%r9;"     /* f[2]*f[0] */
 		"  mulxq 56(%1), %%rax, %%rcx;"    "  adcx %%rax, %%r10;"    /* f[3]*f[0] */
 		"  movq 56(%1), %%rdx;"                                      /* f[3] */

@@ -657,7 +657,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		"  mulxq 48(%1), %%rax, %%rcx;"    "  mov $0, %%r14;"        /* f[2]*f[1] */
 
 		/* Step 2: Compute two parallel carry chains */
-		"  xor %%r15, %%r15;"
+		"  xor %%r15d, %%r15d;"
 		"  adox %%rax, %%r10;"
 		"  adcx %%r8, %%r8;"
 		"  adox %%rcx, %%r11;"

@@ -692,7 +692,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 32(%1), %%r8, %%r13;"
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  adoxq 0(%1), %%r8;"
 		"  mulxq 40(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

@@ -725,7 +725,7 @@ static inline void fsqr2(u64 *out, const u64 *f, u64 *tmp)
 		/* Step 1: Compute dst + carry == tmp_hi * 38 + tmp_lo */
 		"  mov $38, %%rdx;"
 		"  mulxq 96(%1), %%r8, %%r13;"
-		"  xor %%rcx, %%rcx;"
+		"  xor %%ecx, %%ecx;"
 		"  adoxq 64(%1), %%r8;"
 		"  mulxq 104(%1), %%r9, %%rbx;"
 		"  adcx %%r13, %%r9;"

Signature · 1 line

2.26.2

Looks like this is going into HACL in the end, so:

Acked-by Jason A. Donenfeld <[email protected]>

for cryptodev-2.6.git, rather than crypto-2.6.git

Thanks,
Jason

Herbert Xu

maintainer

2020-09-11 06:56 UTC #10 lore raw

In reply to Uros Bizjak

Quoted 10 lines · Uros Bizjak

x86_64 zero extends 32bit operations, so for 64bit operands, XORL r32,r32 is functionally equal to XORL r64,r64, but avoids a REX prefix byte when legacy registers are used.
Signed-off-by Uros Bizjak <[email protected]>
Cc Herbert Xu <[email protected]>
Cc "David S. Miller" <[email protected]>
---
 arch/x86/crypto/curve25519-x86_64.c | 68 ++++++++++++++---------------
 1 file changed, 34 insertions(+), 34 deletions(-)

Patch applied. Thanks.

Signature · 3 lines

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt