RE: [PATCH] Add support for recording xsave x86 instruction

["Metzger, Markus T" <markus.t.metzger@intel.com>]

Hello Pierre,

> On Thu, Sep 27, 2018 at 08:44:44AM +0000, Metzger, Markus T wrote:
> >> +            if (!__get_cpuid_count(0xd, i, &size, &offset, &tmp1, &tmp2))
> >> +              return -1;
> >
> > This would check the native configuration, correct?  What if we
> > recorded remotely on a different x86 box?
> 
> Oops, yes. I don't find how to query the offsets/sizes remotely, however there is
> XSTATE areas sizes in gdb/common/x86-xstate.h. I think we can assume that
> those values are correct.

OK.  Other parts of GDB are using those, as well, rather than querying cpuid.


> > Also I think that we would need to check the inferior architecture to
> > handle 32-bit compatibility mode.
> 
> I'm not sure to follow you. In which cases 32-bit behaves differently than 64-bit ?

Fewer registers.  XSAVE is not writing the upper registers area.


> >> +            if (record_full_arch_list_add_mem (tmpu64 + offset, size))
> >> +              return -1;
> >
> > Looks like this assumes the standard (non-compacted) XSAVE format.
> >
> > For the compacted format, the offset must be computed by accumulating
> > the sizes of preceding components.
> 
> If I'm not mistaken, the compact format is only used by XSAVEC instruction, which
> doesn't have the same opcode. The XSAVE instruction seems unrelated to this
> format.

You're right.  It doesn't write the full header ,though.  And there's a special case
with XCR0[1].


> >> +if ![istarget "*86*-*linux*"] then {
> >> +    verbose "Skipping i386 reverse tests."
> >> +    return
> >> +}
> >
> > Why exclude 64-bit?
> 
> Isn't this roughly the same as:
> [ istarget "x86_64-*linux*" ] && [ istarget "i?86-*linux*" ] thus excluding all arch
> but 32 and 64 bit x86 ?

I mistook it for i?86.

Markus.
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