On Sun, Mar 14, 2021 at 11:07 PM Kaz Kylheku (Coreutils)
<[email protected]> wrote:
>
> On 2021-03-14 12:55, Jeffrey Walton wrote:
> > The underlying problem is GCC, Clang and friends conflate the user's
> > ISA with ISA the compiler uses. They are not the same - they are
> > distinct. Unfortunately, GCC and Clang never addressed the underlying
> > problem.
>
> Sorry, what does that mean?
It means GCC and Clang will generate for the ISA the developer is
using without guarding it.
A developer may do something like:
if (cpu_has_avx())
{
do_crc32_avx();
}
else
{
do_crc32();
}
While Clang and GCC will not guard the code. GCC and Clang will hijack
the developer's ISA and generate code that SIGILL's.
Using Clang I had it happen to me on x86. Clang generated AVX code to
zero a structure because I was using AVX (properly guarded).
Using GCC I had it happen to me on POWER7. GCC used POWER8 in some
prologue because I had some POWER8 code paths (properly guarded).
Jeff
