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

Ulrich Weigand Ulrich.Weigand at de.ibm.com
Fri Mar 25 13:11:16 UTC 2011


Dave Martin <dave.martin at linaro.org> wrote:
> > 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"
>
> Why "LINUX" and not "CORE"?  I don't understand the distinction... are
> the "CORE" notes common to all platforms / all ELF implementations?

Because that's what user_regset_view would do; all notes except the
standard ones (NT_PRPSINFO, NT_PRSTATUS, NT_PRFPREG, NT_AUXV) have a
note name of "LINUX".   I'm not completely sure about the rationale,
but presumably it is indeed because the standard notes are more or less
common across multiple platforms.

> > 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.
>
> It's been suggested that the new note should include a version/flags
> field alongside the ptrace-like register dump, so that if the format
> turns out to be inadequate / broken, it can be extended in a
> compatible way.
>
> However, nothing else in the coredump or the ptrace interface seems to
> have such versioning implementation.  Ptrace gets extended by adding
> more and more ptrace call types instead.  Adding version fields, while
> sensible, seems inconsistent with the current implementation.
>
> What's your view on adding a flags field to the VFP state dump?

Again, if we want to use (or mimic) the user_regset_view mechanism,
there is no choice in any of this; the content of the note will be
exactly identical to the content of the ptrace buffer.  Since this
is the way everybody else is using, I think we'd have to have really
good arguments for deviating from it; I'm not sure I see those.

The usual way to deal with changes to the register set is to define
*new* regset structures, which then translates to new ptrace commands
and new core files notes, which are used instead of or in addition to
the old ones ...


Mit freundlichen Gruessen / Best Regards

Ulrich Weigand

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