RE: [PATCH] gdbserver: Clear X86_XSTATE_MPX bits in xcr0 on x32

["Willgerodt, Felix" <felix.willgerodt@intel.com>]

> -----Original Message-----
> From: H.J. Lu <hjl.tools@gmail.com>
> Sent: Dienstag, 19. März 2024 19:36
> To: GDB <gdb-patches@sourceware.org>; John Baldwin <jhb@freebsd.org>;
> Willgerodt, Felix <felix.willgerodt@intel.com>
> Subject: [PATCH] gdbserver: Clear X86_XSTATE_MPX bits in xcr0 on x32
> 
> Since MPX isn't available for x32, we should clear X86_XSTATE_MPX bits
> on x32.
> 
>         PR server/31511
>         * linux-x86-low.cc (x86_linux_read_description): Clear
>         X86_XSTATE_MPX bits in xcr0 on x32.
> ---
>  gdbserver/linux-x86-low.cc | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/gdbserver/linux-x86-low.cc b/gdbserver/linux-x86-low.cc
> index 3af0a009052..28b5d523b8e 100644
> --- a/gdbserver/linux-x86-low.cc
> +++ b/gdbserver/linux-x86-low.cc
> @@ -938,6 +938,10 @@ x86_linux_read_description (void)
>           xcr0 = xstateregs[(I386_LINUX_XSAVE_XCR0_OFFSET
>                              / sizeof (uint64_t))];
> 
> +         /* No MPX on x32.  */
> +         if (!is_elf64)
> +           xcr0 &= ~X86_XSTATE_MPX;
> +

Doesn't that also disable it for 32-bit?

x86_target::low_siginfo_fixup() uses this to check x32:

  /* No fixup for native x32 GDB.  */
  else if (!is_elf64 && sizeof (void *) == 8)


Felix
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