RFC: ARM: Support for VFP/NEON registers in coredumps

[Ulrich Weigand]

Dave Martin <dave.martin at linaro.org> wrote:
> On Thu, Mar 24, 2011 at 4:40 PM, Ulrich Weigand
<Ulrich.Weigand at de.ibm.com> wrote:
> > I would prefer to keep the contents of NT_VFPREGSET identical to the
> > contents of the PTRACE_GETVPFREGS/PTRACE_SETVPFREGS buffer:
> >
> > - This would allow implementation via the new generic user_regset_view
> >  mechanism (which the ARM kernel doesn't use yet, but probably should)
> >
> > - In any case, GDB likes to have the same set of information available
> >  when debugging core files and native targets
> >
> > So if there is indeed additional information that would be interesting,
> > I'd argue this should be presented as a *new* core file note, *and* as
> > a new set of PTRACE_... APIs.   (But for GDB's purpose NT_AUXV right
> > now is sufficent.  Everything else could be displayed to the user if
> > of interest.)
>
> OK, that sounds reasonable.
>
> If I'm reading the kernel code correctly, the size of the data
> returned by PTRACE_GETVFPREGS is already dependent on the number of
> registers (D16/D32) implemented by the hardware, and this is
> determinable from the auxv contents; so I guess we don't have a new
> problem to solve here.
>
> The other info can always be added in a later pass, if it looks like
> it would be useful...

OK, agreed.

So to summarize: the kernel will write additional note sections as if
generated via user_regset_view, containing the PTRACE_GETVFPREGS data.

Note name: "LINUX"
Note type: t.b.d. [*]

[*] Looking at elf.h a logical name/value might be:

#define NT_ARM_VFP            0x400		/* ARM VFP/NEON registers */


GDB support along those lines ought to be straightforward.



Mit freundlichen Gruessen / Best Regards

Ulrich Weigand

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