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SubjectRe: [PATCH] s390/test_unwind: use raw opcode instead of invalid instruction
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Am 19.11.21 um 02:10 schrieb Nick Desaulniers:
> On Wed, Nov 17, 2021 at 9:48 AM Ilie Halip <ilie.halip@gmail.com> 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@google.com>
>> Signed-off-by: Ilie Halip <ilie.halip@gmail.com>
>
> 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?

e is an instruction format as specified by the architecture.
See http://publibfp.dhe.ibm.com/epubs/pdf/a227832c.pdf
without any parameters.
Normally RR would be the right thing for MVCL, but since
we try to build an invalid opcode without the assembler
noticing (ab)using e seem like a safer approach.

>
> LGTM, thanks again.
> Suggested-by: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

added those and added my RB. applied to the s390 tree. Thanks


>
> 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
>>
>
>

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