[PATCH] x86-64: Stack alignment in _dl_tlsdesc_dynamic and red zone usage (bug 31501)

[H.J. Lu]

On Sat, Mar 16, 2024 at 10:42 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Please verify if this is the right testcase.
>
> Test case works (fails without my fix, succeeds with my fix).  Some
> comments below.
>
> > diff --git a/sysdeps/x86_64/tst-gnu2-tls2-x86-64-mod0.S b/sysdeps/x86_64/tst-gnu2-tls2-x86-64-mod0.S
> > new file mode 100644
> > index 0000000000..8129b28061
> > --- /dev/null
> > +++ b/sysdeps/x86_64/tst-gnu2-tls2-x86-64-mod0.S
> > @@ -0,0 +1,57 @@
>
> > +     .text
> > +     .p2align 4
> > +     .globl  apply_tls
> > +     .type   apply_tls, @function
> > +apply_tls:
> > +     .cfi_startproc
>
> Missing CET marker.
>
> > +     subq    $24, %rsp
> > +     .cfi_def_cfa_offset 32
> > +     movdqu  (%rdi), %xmm0
> > +     movq    %fs:40, %rax
> > +     movq    %rax, 8(%rsp)
> > +     xorl    %eax, %eax
> > +     leaq    tls_var0@TLSDESC(%rip), %rax
> > +     call    *tls_var0@TLSCALL(%rax)
> > +     addq    %fs:0, %rax
> > +     movups  %xmm0, (%rax)
> > +     movdqu  16(%rdi), %xmm1
> > +     movups  %xmm1, 16(%rax)
> > +     movq    8(%rsp), %rdx
> > +     subq    %fs:40, %rdx
> > +     jne     .L5
> > +     addq    $24, %rsp
> > +     .cfi_remember_state
> > +     .cfi_def_cfa_offset 8
> > +     ret
> > +.L5:
> > +     .cfi_restore_state
> > +     call    __stack_chk_fail@PLT
>
> Not sure if we need this?
>
> Maybe add some comment what exactly this subtest is exercising?
>
> These are present in the other TLS modules as well.
>
> > diff --git a/sysdeps/x86_64/tst-gnu2-tls2-x86-64-mod1.S b/sysdeps/x86_64/tst-gnu2-tls2-x86-64-mod1.S
> > new file mode 100644
> > index 0000000000..af4b7ca761
> > --- /dev/null
> > +++ b/sysdeps/x86_64/tst-gnu2-tls2-x86-64-mod1.S
>
> > +/* Select an offset which will cause _dl_tlsdesc_dynamic_xsavec to
> > +   clobber %rbx.  */
> > +#define OFFSET (56 + 16 + 16 + 16)
> > +
> > +     .text
> > +     .p2align 4
> > +     .globl  apply_tls
> > +     .type   apply_tls, @function
> > +apply_tls:
> > +     .cfi_startproc
> > +     pushq   %rbp
> > +     .cfi_def_cfa_offset 16
> > +     .cfi_offset 6, -16
> > +     movq    %rsp, %rbp
> > +     .cfi_def_cfa_register 6
> > +     /* Align stack to 64 bytes.  */
> > +     andq    $-64, %rsp
> > +     pushq   %rbx
> > +     subq    $OFFSET, %rsp
>
> The offset could be loaded from a global variable or something like
> that.  We should exercise a wide range of stack alignments—the
> individual tests are cheap.  And maybe check extra registers.

I will clean it up with a different fix.

-- 
H.J.