Re: [PATCH] s390/test_unwind: use raw opcode instead of invalid instruction

From: Nick Desaulniers
Date: Thu Nov 18 2021 - 20:11:04 EST


On Wed, Nov 17, 2021 at 9:48 AM Ilie Halip <ilie.halip@xxxxxxxxx> wrote:
>
> Building with clang & LLVM_IAS=1 leads to an error:
> arch/s390/lib/test_unwind.c:179:4: error: invalid register pair
> " mvcl %%r1,%%r1\n"
> ^
>
> The test creates an invalid instruction that would trap at runtime, but the
> LLVM inline assembler tries to validate it at compile time too.
>
> Use the raw instruction opcode instead.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1421
> Reported-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Ilie Halip <ilie.halip@xxxxxxxxx>

Ilie, thanks for the patch!

So if I understand
https://sourceware.org/binutils/docs/as/s390-Directives.html#s390-Directives
https://sourceware.org/binutils/docs/as/s390-Formats.html
that `e,` prefix is for 16B opcodes?

LGTM, thanks again.
Suggested-by: Ulrich Weigand <Ulrich.Weigand@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

I triple checked that GAS, clang, and GNU objdump are in agreement in
terms of encoding here.

> ---
> arch/s390/lib/test_unwind.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/s390/lib/test_unwind.c b/arch/s390/lib/test_unwind.c
> index cfc5f5557c06..d342bc884b94 100644
> --- a/arch/s390/lib/test_unwind.c
> +++ b/arch/s390/lib/test_unwind.c
> @@ -176,7 +176,7 @@ static noinline int unwindme_func4(struct unwindme *u)
> * trigger specification exception
> */
> asm volatile(
> - " mvcl %%r1,%%r1\n"
> + " .insn e,0x0e11\n" /* mvcl %%r1,%%r1" */
> "0: nopr %%r7\n"
> EX_TABLE(0b, 0b)
> :);
> --
> 2.25.1
>


--
Thanks,
~Nick Desaulniers