Re: thanks for toolchain + wish support backtrace

[Szabolcs Nagy <nsz@port70.net>]

* Rich Felker <dalias@libc.org> [2019-01-11 16:41:21 -0500]:
> On Fri, Jan 11, 2019 at 09:07:08PM +0000, paradox wrote:
> > hello
> > thanks for toolchain
> > but i need support backtrace function from execinfo.h
> > i mean
> > man 3 backtrace
> > for mips
> > i try 
> > https://musl.cc/mipsel-linux-musln32sf-cross.tgz
> > but can't find execinfo.h
> > 
> > i saw broadcom does support it own build https://github.com/Broadcom/stbgcc-6.3/releases
> > but broadcom don't support softfloat
> > 
> > can you please support in your build a backtrace functions ?
> 
> You can build libbacktrace against musl and it should work. The
> functionality is not provided in musl because it requires a great deal
> of machinery that most users don't need, that has no reason to be
> intertwined with libc, and that makes it impossible to bootstrap a
> toolchain and library ecosystem efficiently (since there would be a
> circular dependency between the unwind library code and libc).

note that if you use backtrace on a system you may
want to build musl itself with -funwind-tables or
even -fasynchronous-unwind-tables in case you need
to unwind from signal handlers, by default musl is
not built that way, you need to set CFLAGS at
configure time to get it (and unwinding across asm
code in musl may not work still), this will increase
the size of libc.

(same is true for any library that takes callbacks
or may be interrupted by signal handlers that try
to use backtrace, but if the software works on other
systems then these are presumably already taken care
of and only the libc needs special attention.)

(the exact requirement for unwinding to work is
target specific, i don't know mips, but the above
mentioned flags sould be enough for c code.)