Re: [PATCH] riscv: Fix ALT_THEAD_PMA's asm parameters
From: Palmer Dabbelt
Date: Fri Jun 17 2022 - 17:54:43 EST
On Mon, 13 Jun 2022 13:26:17 PDT (-0700), nathan@xxxxxxxxxx wrote:
On Wed, May 25, 2022 at 07:40:37PM -0700, Nathan Chancellor wrote:
Small ping on this and https://lore.kernel.org/20220516214520.3252074-1-nathan@xxxxxxxxxx/.
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!
Cheers,
Nathan
On Wed, May 18, 2022 at 11:45:29AM -0700, Nathan Chancellor wrote:
> 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 <jrtc27@xxxxxxxxxx>
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> arch/riscv/include/asm/errata_list.h | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> index 9e2888dbb5b1..416ead0f9a65 100644
> --- a/arch/riscv/include/asm/errata_list.h
> +++ b/arch/riscv/include/asm/errata_list.h
> @@ -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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