Re: Are ppc*_elf_write_core_note Os-specific?

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

On Tue, Jan 19, 2016 at 10:16 AM, John Baldwin <jhb@freebsd.org> wrote:
> On Tuesday, January 19, 2016 08:41:05 AM H.J. Lu wrote:
>> On Mon, Jan 18, 2016 at 7:14 PM, Alan Modra <amodra@gmail.com> wrote:
>> > On Tue, Jan 19, 2016 at 10:48:19AM +1030, Alan Modra wrote:
>> >> PowerPC64 glibc even now doesn't defing prstatus32_t.  :-(  It seems
>> >> only sparc and s390 do so.  So PowerPC would need a
>> >> hosts/powerpc-linux.h to define them for Linux, with some configury
>> >> changes, like hosts/x86-64linux.h does for x86-64 Linux.  I'll see
>> >> about making those changes.
>> >>
>> >> Note that elf_backend_write_core_note is defined for x86-64, arm and
>> >> aarch64 too.  The ARM and AARCH64 functions look to be completely
>> >> redundant, and I suspect all of them could disappear if we modify the
>> >> generic code to handle prstatusx32_t for x86-64.
>> >
>> > Actually, there is a reason for the ARM and AARCH64 functions.
>> > See https://sourceware.org/ml/binutils/2011-10/msg00202.html
>> > Note the followup emails too..
>> >
>> > So it seems that with the current infrastructure we can either support
>> > core file generation on remote (linux) targets, or core file
>> > generation on more native targets (freebsd).  Alternatively, we'd
>> > need to use separate bfd target vectors for linux and freebsd, which
>> > can and will cause multiple target matches.
>> >
>> > Do we really want non-native core file generation?
>> >
>>
>> Any changes shouldn't introduce regressions.  I don't see why
>> elf_backend_write_core_note can't handle all targets BFD supports
>> since note_type is unique to each OS.  BFD just needs to provide
>> proper types independent of host header files, similar to
>> hosts/x86-64linux.h.
>
> Switching on note_type alone (as the current write_core_note methods do)
> isn't sufficient.   Currently bfd writes out notes like NT_PRSTATUS and
> NT_PRPSINFO with the "CORE" name on multiple platforms, so a
> (note_name, note_type) tuple also seems insufficient.  Are you suggesting
> to switch on (ELF OSABI, note_type)?  That is, supposing you had a
> hosts/x86-64freebsd.h with a 'struct freebsd_amd64_prstatus' and if
> hosts/x86-64linux.h had 'struct linux_x86_64_prstatus' (or whatever names
> are preferred), then the logic in the write_core_note would look something
> like:
>
>   switch (get_elf_backend_data (abfd)->elf_osabi)
>     {
>       case ELFOSABI_FREEBSD:
>         {
>           switch (note_type)
>             {
>               case NT_PRSTATUS:
>                  struct freebsd_amd64_prstatus prstatus;
>                  ...
>                  return elfcore_write_note (abfd, ... &prstatus, ...);
>               ...
>             }
>           ...
>         }
>       case ELFOSABI_LINUX:
>         {
>           switch (note_type)
>             {
>               case NT_PRSTATUS:
>                  struct linux_x86_64_prstatus prstatus;
>                  ...
>                  return elfcore_write_note (abfd, ... &prstatus, ...);
>               ...
>             }
>           ...
>         }
>       ..
>     }
>
> If so, checking elf_osabi in the current write_core_note functions and
> falling back to the native "catch-all" if it is not a currently-supported
> elf_osabi would be sufficient to preserve existing functionality (I think)
> while allowing other ABIs to either use the catch-all or implement support
> for desired non-native cores.

How does GDB tell Linux binary from FreeBSD binary?

-- 
H.J.