Re: [PATCH v6 00/15] Handle variable XSAVE layouts

Keith Seitz via Gdb-patches
2023-07-27T21:36:52Z

On 7/26/23 15:31, John Baldwin wrote:
>
> So I have a couple of things to try here.  First, a simple fix for the crash
> is this change (relative to the branch), but it does mean the core dumps generated
> by gcore for a remote target will not contain extended XSAVE state like AVX, etc.:
>
> diff --git a/gdb/i386-linux-tdep.c b/gdb/i386-linux-tdep.c
> index c8b467a0416..a7d61f33a08 100644
> --- a/gdb/i386-linux-tdep.c
> +++ b/gdb/i386-linux-tdep.c
> @@ -768,7 +768,7 @@ i386_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>
>    cb (".reg", 68, 68, &i386_gregset, NULL, cb_data);
>
> -  if (tdep->xcr0 & X86_XSTATE_AVX)
> +  if (tdep->xsave_layout.sizeof_xsave != 0)
>      cb (".reg-xstate", tdep->xsave_layout.sizeof_xsave,
>         tdep->xsave_layout.sizeof_xsave, &i386_linux_xstateregset,
>         "XSAVE extended state", cb_data);
>
> Arguably that is more correct as it lines up with the way the rest of the x86 arches
> in this series.

Yeah, that does fix a lot of problems. In the vein of "perfect is the enemy of good,"
this LGTM.

> The other change I have locally is one to generate a "fallback" layout to use in
> this case that a target (such as remote) doesn't provide a layout.

>
> The fallback change:
[snip]

This causes a new regression in gdb.base/solib-display.exp:

# make check RUNTESTFLAGS="--target_board native-extended-gdbserver.exp" \
TESTS=gdb.base/solib-display.exp
Running /root/fsf/linux/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/solib-display.exp ...
FAIL: gdb.base/solib-display.exp: NO: continue two
FAIL: gdb.base/solib-display.exp: IN: continue two
FAIL: gdb.base/solib-display.exp: SEP: continue two

=== gdb Summary ===

# of expected passes 32
# of unexpected failures 3

The issue is the same with all three failing tests (-m32/-m64 don't matter).
With this tweak, we now see:

warning: Unable to display "a_local": No symbol "a_local" in current context.
warning: Unable to display "a_static": No symbol "a_static" in current context.

This disables the display of the two variables, and they are omitted from
subsequent displays. [This happens on every x86_64 on which I've tested: Comet Lake,
Raptor Lake, and Sapphire Rapids.]

Keith