[Bug target/113874] New: GNU2 TLS descriptor calls do not follow psABI on x86_64-linux-gnu

[fw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113874

            Bug ID: 113874
           Summary: GNU2 TLS descriptor calls do not follow psABI on
                    x86_64-linux-gnu
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fw at gcc dot gnu.org
  Target Milestone: ---
            Target: x86_64-linux-gnu

Consider this test case:

struct tls {
  long a, b, c, d;
};

extern __thread struct tls tls_var __attribute__ ((visibility ("hidden")));

void
apply_tls (struct tls *p)
{
  tls_var = *p;
}

With “-O2 -fpic -mtls-dialect=gnu2“, it gets compiled to:

apply_tls:
.LFB0:
        .cfi_startproc
        subq    $8, %rsp
        .cfi_def_cfa_offset 16
        movdqu  (%rdi), %xmm0
        leaq    tls_var@TLSDESC(%rip), %rax
        call    *tls_var@TLSCALL(%rax)
        addq    %fs:0, %rax
        movups  %xmm0, (%rax)
        movdqu  16(%rdi), %xmm1
        movups  %xmm1, 16(%rax)
        addq    $8, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc

Note how %xmm0 is loaded before the descriptor call. The glibc implementation
assumes psABI, so %xmm0 is potentially clobbered by the call.

Discovered as a crash in the polymake testsuite
(/fan/objects/Geometry/PolyhedralFan/properties/Combinatorics/DUAL_GRAPH) if
its dependency nauty is compiled with -mtls-dialect=gnu2.

(i686-linux-gnu has the same issue with -msse2.)