Introduce __fill_user() and kill __bzero()

Currently memset() is used to fill a user space area (clear_user) or kernel one (memset). These two functions don't have the same prototype, the former returning the number of bytes not copied and the latter returning the start address of the area to clear. This forces memset() to actually returns two values in an unconventional way ie the number of bytes not copied is given by $a2. Therefore clear_user() needs to call memset() using inline assembly.

Instead this patch creates __fill_user() which is the same as memset() except it always returns the number of bytes not copied. This simplify clear_user() and makes its definition saner.

Also an out of line version of memset is given because gcc generates some calls to it since builtin functions have been disabled. It allows assembly code to call it too.

Eventually __bzero() has been removed because it's not part of the Linux uaccess API. And the nano-optimization it brings is not worthing.

Signed-off-by Franck Bui-Huu <[email protected]>

---
 arch/mips/kernel/mips_ksyms.c |    3 +-
 arch/mips/lib/csum_partial.S  |    2 +-
 arch/mips/lib/memcpy.S        |    2 +-
 arch/mips/lib/memset.S        |   49 ++++++++++++++++++++++++++--------------
 include/asm-mips/string.h     |    7 +++++-
 include/asm-mips/uaccess.h    |   17 ++-----------
 6 files changed, 44 insertions(+), 36 deletions(-)

arch/mips/kernel/mips_ksyms.c +1 -2

index 225755d..a801e09 100644
@@ -14,7 +14,6 @@
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
 
-extern void *__bzero(void *__s, size_t __count);
 extern long __strncpy_from_user_nocheck_asm(char *__to,
                                             const char *__from, long __len);
 extern long __strncpy_from_user_asm(char *__to, const char *__from,

@@ -36,9 +35,9 @@ EXPORT_SYMBOL(kernel_thread);
 /*
  * Userspace access stuff.
  */
+EXPORT_SYMBOL(__fill_user);
 EXPORT_SYMBOL(__copy_user);
 EXPORT_SYMBOL(__copy_user_inatomic);
-EXPORT_SYMBOL(__bzero);
 EXPORT_SYMBOL(__strncpy_from_user_nocheck_asm);
 EXPORT_SYMBOL(__strncpy_from_user_asm);
 EXPORT_SYMBOL(__strlen_user_nocheck_asm);

arch/mips/lib/csum_partial.S +1 -1

index c0a77fe..8d3fa1e 100644
@@ -694,7 +694,7 @@ l_exc:
 	ADD	dst, t0			# compute start address in a1
 	SUB	dst, src
 	/*
-	 * Clear len bytes starting at dst.  Can't call __bzero because it
+	 * Clear len bytes starting at dst.  Can't call memset because it
 	 * might modify len.  An inefficient loop for these rare times...
 	 */
 	beqz	len, done

arch/mips/lib/memcpy.S +1 -1

index a526c62..425f2c3 100644
@@ -443,7 +443,7 @@ l_exc:
 	ADD	dst, t0			# compute start address in a1
 	SUB	dst, src
 	/*
-	 * Clear len bytes starting at dst.  Can't call __bzero because it
+	 * Clear len bytes starting at dst.  Can't call memset because it
 	 * might modify len.  An inefficient loop for these rare times...
 	 */
 	beqz	len, done

arch/mips/lib/memset.S +3 -1

index 3f8b8b3..cb6b83d 100644
@@ -46,17 +46,34 @@
 	.endm
 
 /*
- * memset(void *s, int c, size_t n)
+ * An outline version of memset, which should be used either by gcc or
+ * by assembly code.
+ */

Quoted 9 lines

/*
- * memset(void *s, int c, size_t n)
+ * An outline version of memset, which should be used either by gcc or
+ * by assembly code.
+ */

arch/mips/lib/memset.S +4 -0

+NESTED(memset, 24, ra)
+	PTR_ADDU	sp, sp, -24
+	LONG_S		a0, 16(sp)
+	LONG_S		ra, 20(sp)

arch/mips/lib/memset.S line 61

Quoted 6 lines

arch/mips/lib/memset.S +6 -0

+	jal		__fill_user
+	LONG_L		v0, 16(sp)
+	LONG_L		ra, 20(sp)
+	PTR_ADDU	sp, sp, 24
+	jr		ra
+END(memset)

This will break on 64bit kernels.

Quoted 9 lines · Franck Bui-Huu

/*
- * memset(void *s, int c, size_t n)
+ * An outline version of memset, which should be used either by gcc or
+ * by assembly code.
+ */

arch/mips/lib/memset.S +4 -0

+NESTED(memset, 24, ra)
+	PTR_ADDU	sp, sp, -24
+	LONG_S		a0, 16(sp)
+	LONG_S		ra, 20(sp)

arch/mips/lib/memset.S line 61

Quoted 6 lines

arch/mips/lib/memset.S +6 -0

+	jal		__fill_user
+	LONG_L		v0, 16(sp)
+	LONG_L		ra, 20(sp)
+	PTR_ADDU	sp, sp, 24
+	jr		ra
+END(memset)

This will break on 64bit kernels.

Quoted 10 lines · Thiemo Seufer

Quoted 9 lines · Franck Bui-Huu

/*
- * memset(void *s, int c, size_t n)
+ * An outline version of memset, which should be used either by gcc or
+ * by assembly code.
+ */

arch/mips/lib/memset.S +4 -0

+NESTED(memset, 24, ra)
+	PTR_ADDU	sp, sp, -24
+	LONG_S		a0, 16(sp)
+	LONG_S		ra, 20(sp)

Quoted 9 lines

arch/mips/lib/memset.S line 61

Quoted 6 lines

arch/mips/lib/memset.S +6 -0

+	jal		__fill_user
+	LONG_L		v0, 16(sp)
+	LONG_L		ra, 20(sp)
+	PTR_ADDU	sp, sp, 24
+	jr		ra
+END(memset)

This will break on 64bit kernels.

Is the following correct ?

NESTED(memset, 16, ra)

        PTR_ADDU        sp, sp, -16
        LONG_S          a0,  8(sp)
        LONG_S          ra, 16(sp)
        jal             __fill_user
        LONG_L          v0,  8(sp)
        LONG_L          ra, 16(sp)
        PTR_ADDU        sp, sp, 16
        jr              ra

END(memset)

I know it doesn't respect any mips ABI but in this case do we really care ?

In general we do (think of stack unwinding etc.). I believe this implementation should move to C, as it doesn't need an assembler implementation:

void *memset (void *s, int c, kernel_size_t n)

{
	__fill_user(s, c, n);
	return s;
}

It looks much nicer that way. :-)

Quoted 10 lines · Thiemo Seufer

In general we do (think of stack unwinding etc.). I believe this implementation should move to C, as it doesn't need an assembler implementation:

void *memset (void *s, int c, kernel_size_t n)

{
	__fill_user(s, c, n);
	return s;
}

Quoted 2 lines

It looks much nicer that way. :-)

Sure but memset.S was a really good place to implement memset(), wasn't it ?

And since the implementation should have been trivial,

I thought it was ok to implement in assembly.

What about using memset.c and fill_user.S ?