svn commit: r307231 - head/lib/libgcc_s

[Ed Maste]

Hi Bruce, thank you for the detailed response.

On 14 October 2016 at 01:53, Bruce Evans <brde at optusnet.com.au> wrote:
>>  compiler-rt's complex division support routines contain calls to
>>  compiler builtins such as `__builtin_scalbnl`.  Unfortunately Clang
>>  turns these back into a call to `scalbnl`.
>
> gcc-4.2 has the same bug.

Oh, interesting. Do you know off hand if it's resolved in later GCC?

It seems particularly unfortunate for the compiler to report (by
whatever mechanism) that a builtin exists, and then just turn that
builtin into a library call.

>>  For now link libm's C version of the required support routines.
>
> Even libm doesn't use these in some cases.  i386 mostly uses asm
> versions.  Hopefully the rt division routines don't need to be efficient
> because they are rarely called.

Most likely I'll switch to the asm versions across suitable
architectures in a subsequent change, mirroring the choices made in
libm.  I just wanted to get a version in, to enable further testing
(ports exp-runs, etc.) of this libunwind / compiler-rt combination.

[Details about specific groups of functions omitted -- I'll try to
take a look at these later.]

> libcompiler_rt.a now on amd64 now has the following namespace bugs:
>
>                  U compilerrt_abort_impl
>                  U fflush
>                  U fprintf
>                  U mprotect
>                  U sysconf
>                  U fmaxl
>                  U logbl
>                  U scalbnl
>                  U logbf
>                  U scalbnf
>                  U logb
>                  U scalbn
>                  U abort
>
> These are bugs since division must be available with -ffreestanding and
> the freestanding library shouldn't have to reimplement it.

Yes, these libcompiler_rt.a issues seem rather surprising to me, but
presumably they aren't causing much of an issue in practice in the
static lib. In any case, my hope is that once I try disentangling
these libraries I can take a look at these issues across the set of
libraries (libcompiler_rt.a aka libgcc.a, libgcc_eh.a, libgcc_s.so).