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SubjectRe: [PATCH v2] x86: fix early boot crash on gcc-10
On Wed, Apr 22, 2020 at 04:16:53PM +0200, Martin Liška wrote:
> And as I talked to Boris, I would recommend to come up with a "configure" check
> that a compiler does not optimize the key code sequence:
>
> $ cat asm-detect.c
> int foo(int a);
> int bar(int a)
> {
> int r = foo(a);
> asm ("");
> return r;
> }
>
> $ gcc -O2 -c asm-detect.c -S -o/dev/stdout | grep jmp
> [no output]

That is a good test to run at the beginning of the compilation I guess.

Without the asm("") it produces:

bar:
.LFB0:
.cfi_startproc
jmp foo@PLT
.cfi_endproc

I'd like for LLVM folks to confirm that this is a good test for LLVM too
Trying that here with clang gives:

bar: # @bar
.cfi_startproc
# %bb.0:
jmp foo # TAILCALL
.Lfunc_end0:

so this *looks* like it would work with LLVM too but I might be missing
something...

Thx.

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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