Public bug reported:
I am trying to use ifunc
On good architectures like armhf & arm64, glibc passes hwcaps argument
to the ifunc resolver function, which one can use to test for various
features.
On x86_64, no argument is passed, thus I'm trying to use
__builtin_cpu_supports() function instead. It would be nice if glibc did
pass something like whatever __builtin_cpu_supports() needs.
However, it seems like __builtin_cpu_supports is unusable from inside
ifunc resolver. Re-implementing __builtin_cpu_supports with __get_cpuid
works.
Using __builtin_cpu_supports in main() otherwise works.
Is my code wrong, or can gcc/glibc be improved, such that
__builtin_cpu_supports works in an ifunc resolver?
See attached code.
$ gcc-10 test_builtin_ifunc.c -o test_builtin_ifunc
$ ./test_builtin_ifunc
sse41
portable
sse41
Whereas on a machine that supports SSE4.1 the expected output is
sse41
sse41
sse41
** Affects: gcc-10 (Ubuntu)
Importance: Undecided
Status: Invalid
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: Invalid
** Also affects: glibc (Ubuntu)
Importance: Undecided
Status: New
** Description changed:
I am trying to use ifunc
On good architectures like armhf & arm64, glibc passes hwcaps argument
to the ifunc resolver function, which one can use to test for various
features.
On x86_64, no argument is passed, thus I'm trying to use
- __builtin_cpu_supports() function instead.
+ __builtin_cpu_supports() function instead. It would be nice if glibc did
+ pass something like whatever __builtin_cpu_supports() needs.
However, it seems like __builtin_cpu_supports is unusable from inside
ifunc resolver. Re-implementing __builtin_cpu_supports with __get_cpuid
works.
Using __builtin_cpu_supports in main() otherwise works.
Is my code wrong, or can gcc/glibc be improved, such that
__builtin_cpu_supports works in an ifunc resolver?
See attached code.
$ gcc-10 test_builtin_ifunc.c -o test_builtin_ifunc
$ ./test_builtin_ifunc
sse41
portable
sse41
Whereas on a machine that supports SSE4.1 the expected output is
sse41
sse41
sse41
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https://bugs.launchpad.net/bugs/1884382
Title:
__builtin_cpu_supports does not work in ifunc resolver
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