Re: [PATCH] powerpc: Remove backtrace implementation

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella via Libc-alpha:

> Afaik this is true for every other architecture that uses libgcc for
> backtrace implementation, currently *everything* but powerpc and
> microblaze:
>
> This is on aarch64 with gcc 5.4:
>
> $ gcc -g0 -fno-asynchronous-unwind-tables backtrace.c -o backtrace
> $ ./backtrace 3
> backtrace() returned 1 addresses
> ./backtrace() [0x4009dc]
>
> And this is sparc64 with gcc-10:
>
> $ gcc -g0 -fno-asynchronous-unwind-tables backtrace.c -o backtrace
> $ ./backtrace 3
> backtrace() returned 1 addresses
> ./backtrace(+0xa74) [0x10000000a74]
>
> So for all other architectures we require -fasynchronous-unwind-tables
> to get backtrace work and I plan to remove microblaze implementation
> so powerpc will be only outlier.

GCC's defaults matter as well, I think.  If GCC defaults to unwind
tables (is -funwind-tables sufficient?), then the libgcc_s unwinder will
work for default builds.

The libgcc_s unwinder may also have custom backchain logic for some
targets, I haven't checked.

Part of the challenge here is whether people consider unwind tables or
frame pointers part of the ABI.  There doesn't seem to be consensus,
even for Linux targets (I think people on the musl side dislike the
tables).

Thanks,
Florian