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

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Mar 20, 2024 at 1:40 AM Willgerodt, Felix
<felix.willgerodt@intel.com> wrote:
>
> > -----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?

Fixed in the v2 patch with

+    /* No MPX on x32.  */
+    if (machine == EM_X86_64 && !is_elf64)
+      xcr0 &= ~X86_XSTATE_MPX;
+

> x86_target::low_siginfo_fixup() uses this to check x32:
>
>   /* No fixup for native x32 GDB.  */
>   else if (!is_elf64 && sizeof (void *) == 8)
>
>

Thanks.

-- 
H.J.