riscv: Fix ALT_THEAD_PMA's asm parameters

PATCH In review Nathan Chancellor 4 participants 7 messages May 18, 2022 – Jun 17, 2022 RISC-V

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Nathan Chancellor

author

2022-05-18 18:45 UTC #0 lore raw

PATCH 1/1 riscv: Fix ALT_THEAD_PMA's asm parameters

After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:

In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm

          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^

This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:

* t3 is modified but not listed in the clobbers list.

* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.

Drop the matching contraint and shift all the operands by one, as %1 is unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.

Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")

Link https://github.com/ClangBuiltLinux/linux/issues/1641

Link https://github.com/llvm/llvm-project/issues/55514

Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html

Signed-off-by Nathan Chancellor <[email protected]>

---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

arch/riscv/include/asm/errata_list.h +7 -7

index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(						\
 	"nop\n\t"							\
 	"nop\n\t"							\
 	"nop",								\
-	"li      t3, %2\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %1\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
 	"bne     t3, zero, 2f\n\t"					\
-	"li      t3, %3\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"or      %0, %0, t3\n\t"					\
 	"2:",  THEAD_VENDOR_ID,						\
 		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
 	: "+r"(_val)							\
-	: "0"(_val),							\
-	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
 	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
-	  "I"(ALT_THEAD_PBMT_SHIFT))
+	  "I"(ALT_THEAD_PBMT_SHIFT)					\
+	: "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif

base-commit: 93c0651617a62a69717299f1464dda798af8bebb

Signature · 1 line

2.36.1

Nick Desaulniers

Reviewed-by on v1 1/1

2022-05-18 20:45 UTC #1 lore raw

Quoted 20 lines · Nathan Chancellor

After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^
This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.

Quoted 7 lines

* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is

s/contraint/constraint/

Thanks for the fix!

Reviewed-by Nick Desaulniers <[email protected]>

Quoted 50 lines

unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.

Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")

Link https://github.com/ClangBuiltLinux/linux/issues/1641

Link https://github.com/llvm/llvm-project/issues/55514

Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html

Signed-off-by Nathan Chancellor <[email protected]>

---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

arch/riscv/include/asm/errata_list.h +7 -7

index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(                                           \
        "nop\n\t"                                                       \
        "nop\n\t"                                                       \
        "nop",                                                          \
-       "li      t3, %2\n\t"                                            \
-       "slli    t3, t3, %4\n\t"                                        \
+       "li      t3, %1\n\t"                                            \
+       "slli    t3, t3, %3\n\t"                                        \
        "and     t3, %0, t3\n\t"                                        \
        "bne     t3, zero, 2f\n\t"                                      \
-       "li      t3, %3\n\t"                                            \
-       "slli    t3, t3, %4\n\t"                                        \
+       "li      t3, %2\n\t"                                            \
+       "slli    t3, t3, %3\n\t"                                        \
        "or      %0, %0, t3\n\t"                                        \
        "2:",  THEAD_VENDOR_ID,                                         \
                ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)            \
        : "+r"(_val)                                                    \
-       : "0"(_val),                                                    \
-         "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),              \
+       : "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),              \
          "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),                 \
-         "I"(ALT_THEAD_PBMT_SHIFT))
+         "I"(ALT_THEAD_PBMT_SHIFT)                                     \
+       : "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif

base-commit: 93c0651617a62a69717299f1464dda798af8bebb --
2.36.1

Signature · 2 lines

Thanks,
~Nick Desaulniers

Heiko Stübner

Reviewed-by Tested-by on v1 1/1

2022-05-19 07:22 UTC #2 lore raw

In reply to Nathan Chancellor

Am Mittwoch, 18. Mai 2022, 20:45:29 CEST schrieb Nathan Chancellor:

Quoted 29 lines

After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^
This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.
* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.

Quoted 6 lines

Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")
Link https://github.com/ClangBuiltLinux/linux/issues/1641
Link https://github.com/llvm/llvm-project/issues/55514
Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
Suggested-by Jessica Clarke <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>

I'm not sure anymore why it ended up the original way, but with this change it definitly looks better

Reviewed-by Heiko Stuebner <[email protected]>

On an actual D1-Nezha board also

Tested-by Heiko Stuebner <[email protected]>

Thanks for doing that improvement
Heiko

Quoted 39 lines

---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

arch/riscv/include/asm/errata_list.h +7 -7

index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(						\
 	"nop\n\t"							\
 	"nop\n\t"							\
 	"nop",								\
-	"li      t3, %2\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %1\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
 	"bne     t3, zero, 2f\n\t"					\
-	"li      t3, %3\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"or      %0, %0, t3\n\t"					\
 	"2:",  THEAD_VENDOR_ID,						\
 		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
 	: "+r"(_val)							\
-	: "0"(_val),							\
-	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
 	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
-	  "I"(ALT_THEAD_PBMT_SHIFT))
+	  "I"(ALT_THEAD_PBMT_SHIFT)					\
+	: "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif

base-commit: 93c0651617a62a69717299f1464dda798af8bebb

Nathan Chancellor

author

2022-05-26 02:40 UTC #3 lore raw

In reply to Nathan Chancellor

Small ping on this and https://lore.kernel.org/[email protected]/.

Our builds on -next have been broken for a week now. Hopefully these can make the first RISC-V pull request to avoid mainline being broken in the same fashion.

Cheers,
Nathan

Quoted 81 lines · Nathan Chancellor

After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^
This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.
* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.
Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")
Link https://github.com/ClangBuiltLinux/linux/issues/1641
Link https://github.com/llvm/llvm-project/issues/55514
Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
Suggested-by Jessica Clarke <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>
---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)
arch/riscv/include/asm/errata_list.h +7 -7
index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(						\
 	"nop\n\t"							\
 	"nop\n\t"							\
 	"nop",								\
-	"li      t3, %2\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %1\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
 	"bne     t3, zero, 2f\n\t"					\
-	"li      t3, %3\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"or      %0, %0, t3\n\t"					\
 	"2:",  THEAD_VENDOR_ID,						\
 		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
 	: "+r"(_val)							\
-	: "0"(_val),							\
-	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
 	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
-	  "I"(ALT_THEAD_PBMT_SHIFT))
+	  "I"(ALT_THEAD_PBMT_SHIFT)					\
+	: "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif
base-commit: 93c0651617a62a69717299f1464dda798af8bebb
Signature · 7 lines
2.36.1


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linux-riscv mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-riscv

Nathan Chancellor

author

2022-06-13 20:26 UTC #4 lore raw

Quoted 5 lines · Nathan Chancellor

Small ping on this and https://lore.kernel.org/[email protected]/.
Our builds on -next have been broken for a week now. Hopefully these can make the first RISC-V pull request to avoid mainline being broken in the same fashion.

One more small ping. The patch linked above made it into 5.19-rc1 but this one has not been applied so our builds are still broken.

Cheers,
Nathan

Quoted 83 lines · Nathan Chancellor

Quoted 81 lines
After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^
This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.
* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.
Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")
Link https://github.com/ClangBuiltLinux/linux/issues/1641
Link https://github.com/llvm/llvm-project/issues/55514
Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
Suggested-by Jessica Clarke <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>
---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)
arch/riscv/include/asm/errata_list.h +7 -7
index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(						\
 	"nop\n\t"							\
 	"nop\n\t"							\
 	"nop",								\
-	"li      t3, %2\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %1\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
 	"bne     t3, zero, 2f\n\t"					\
-	"li      t3, %3\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"or      %0, %0, t3\n\t"					\
 	"2:",  THEAD_VENDOR_ID,						\
 		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
 	: "+r"(_val)							\
-	: "0"(_val),							\
-	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
 	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
-	  "I"(ALT_THEAD_PBMT_SHIFT))
+	  "I"(ALT_THEAD_PBMT_SHIFT)					\
+	: "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif
base-commit: 93c0651617a62a69717299f1464dda798af8bebb
Signature · 7 lines
2.36.1


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Palmer Dabbelt

maintainer

2022-06-17 21:54 UTC #5 lore raw

Quoted 9 lines · On Mon, 13 Jun 2022 13:26:17 PDT (-0700), [email protected] wrote:

Quoted 5 lines · Nathan Chancellor
Small ping on this and https://lore.kernel.org/[email protected]/.
Our builds on -next have been broken for a week now. Hopefully these can make the first RISC-V pull request to avoid mainline being broken in the same fashion.
One more small ping. The patch linked above made it into 5.19-rc1 but this one has not been applied so our builds are still broken.

Sorry I dropped the ball on this one, it's in fixes. Thanks!

Quoted 86 lines

Cheers,
Nathan
Quoted 83 lines · Nathan Chancellor
Quoted 81 lines
After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^
This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.
* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.
Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")
Link https://github.com/ClangBuiltLinux/linux/issues/1641
Link https://github.com/llvm/llvm-project/issues/55514
Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
Suggested-by Jessica Clarke <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>
---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)
arch/riscv/include/asm/errata_list.h +7 -7
index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(						\
 	"nop\n\t"							\
 	"nop\n\t"							\
 	"nop",								\
-	"li      t3, %2\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %1\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
 	"bne     t3, zero, 2f\n\t"					\
-	"li      t3, %3\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"or      %0, %0, t3\n\t"					\
 	"2:",  THEAD_VENDOR_ID,						\
 		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
 	: "+r"(_val)							\
-	: "0"(_val),							\
-	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
 	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
-	  "I"(ALT_THEAD_PBMT_SHIFT))
+	  "I"(ALT_THEAD_PBMT_SHIFT)					\
+	: "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif
base-commit: 93c0651617a62a69717299f1464dda798af8bebb --
2.36.1
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Nathan Chancellor

author

2022-06-17 21:57 UTC #6 lore raw

Quoted 4 lines · Palmer Dabbelt

Quoted 3 lines · On Mon, 13 Jun 2022 13:26:17 PDT (-0700), [email protected] wrote:
Quoted 2 lines · Nathan Chancellor
Small ping on this and https://lore.kernel.org/[email protected]/.

Quoted 8 lines

Quoted 6 lines
Quoted 3 lines
Our builds on -next have been broken for a week now. Hopefully these can make the first RISC-V pull request to avoid mainline being broken in the same fashion.
One more small ping. The patch linked above made it into 5.19-rc1 but this one has not been applied so our builds are still broken.
Sorry I dropped the ball on this one, it's in fixes. Thanks!

Better late than never :) thanks a lot!

Cheers,
Nathan

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Quoted 83 lines · Nathan Chancellor
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After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"), builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
          ALT_THEAD_PMA(prot_val);
          ^
  ./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
          : "0"(_val),                                                    \
            ^
This was reported upstream to LLVM where Jessica pointed out a couple of issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.
* "+r"(_val) marks _val as both an input and output of the asm but then "0"(_val) marks _val as an input matching constraint, which does not make much sense in this situation, as %1 is not actually used in the asm and matching constraints are designed to be used for different inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is unused, and mark t3 as clobbered. This resolves the build error and goes not cause any problems with GNU as.
Fixes a35707c3d850 ("riscv: add memory-type errata for T-Head")
Link https://github.com/ClangBuiltLinux/linux/issues/1641
Link https://github.com/llvm/llvm-project/issues/55514
Link https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
Suggested-by Jessica Clarke <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>
---
 arch/riscv/include/asm/errata_list.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)
arch/riscv/include/asm/errata_list.h +7 -7
index 9e2888dbb5b1..416ead0f9a65 100644
@@ -75,20 +75,20 @@ asm volatile(ALTERNATIVE(						\
 	"nop\n\t"							\
 	"nop\n\t"							\
 	"nop",								\
-	"li      t3, %2\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %1\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
 	"bne     t3, zero, 2f\n\t"					\
-	"li      t3, %3\n\t"						\
-	"slli    t3, t3, %4\n\t"					\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %3\n\t"					\
 	"or      %0, %0, t3\n\t"					\
 	"2:",  THEAD_VENDOR_ID,						\
 		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
 	: "+r"(_val)							\
-	: "0"(_val),							\
-	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	: "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
 	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
-	  "I"(ALT_THEAD_PBMT_SHIFT))
+	  "I"(ALT_THEAD_PBMT_SHIFT)					\
+	: "t3")
 #else
 #define ALT_THEAD_PMA(_val)
 #endif
base-commit: 93c0651617a62a69717299f1464dda798af8bebb --
2.36.1
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