BusyBox 1.36.0 regression: Segfaults on i386 musl libc

[Sören Tempel]

Hello,

Natanael Copa <ncopa at alpinelinux.org> wrote:
> diff --git a/libbb/hash_md5_sha.c b/libbb/hash_md5_sha.c
> index 880ffab01..d2351d3e6 100644
> --- a/libbb/hash_md5_sha.c
> +++ b/libbb/hash_md5_sha.c
> @@ -17,8 +17,11 @@
>  # if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
>  static void cpuid(unsigned *eax, unsigned *ebx, unsigned *ecx, unsigned *edx)
>  {
> -       asm ("cpuid"
> -               : "=a"(*eax), "=b"(*ebx), "=c"(*ecx), "=d"(*edx)
> +       asm volatile (
> +               "mov %%ebx, %%esi;" /* save %ebx PIC register */
> +               "cpuid;"
> +               "xchg %%ebx, %%esi;"
> +               : "=a"(*eax), "=S"(*ebx), "=c"(*ecx), "=d"(*edx)
>                 : "0"(*eax),  "1"(*ebx),  "2"(*ecx),  "3"(*edx)
>         );
>  }

Unfortunately, this does not fix the segfault. Since the segfault occurs
in musl's dynamic loader I also don't think that this code is
reached/executed. Instead, this seems to be a problem with the symbols
of the provided assembly file.

I am currently debugging this on a96ccbefe417aaac6a2ce59c788e01fc0f83902f.
If I remove the PSHUFFLE_BYTE_FLIP_MASK definition (and the instruction
using it) in hash_md5_sha256_x86-32_shaNI.S from the checkout for this
commit then the segfault doesn't occur. So this does definitely seem to
be a problem with the hash_md5_sha256_x86-32_shaNI.S assembly file...

Greetings,
Sören