Re: Static linking of musl with code compiled using GNU header files

[Szabolcs Nagy <nsz@port70.net>]

* David Grothe <dave@gcom.com> [2014-03-14 10:47:31 -0500]:
> I have a very large code base that I have been compiling on Linux
> using the standard GNU C compiler [gcc (Ubuntu/Linaro
> 4.6.3-1ubuntu5) 4.6.3].  I have been using shared object libraries,
> but for reasons of software support I would now like to link all my
> commands (a couple of dozen) and daemons using static libraries so
> that the code files are self-contained and can be copied, along with
> a core file, to any server back in my shop for analysis.  With
> dynamic libraries I have to have exactly the same version of libc
> installed on the machine that I use to examine the core file as were
> present on the machine that generated the core file, or else gdb
> will not produce a stack back trace with file and line number
> information.  So much for the background.
> 
> I really don't want to port my code base to using the musl header
> files.  I want to keep compiling with the GNU headers.  When I do

compiling with the gnu headers is broken and
it depends on the cflags used

> this and link my-huge-program.o with musl libc.a I get the following
> list of unresolved externals:
> 
>          U __divdi3

comes from libgcc.a, if it's missing you have a toolchain issue

>          w __fini_array_end
>          w __fini_array_start

i think musl supports init/fini arrays
(see src/exit/exit.c)

>          U __moddi3

libgcc

>          U __sysv_signal

you may want to replace it with signal

>          U __udivdi3
>          U __umoddi3

libgcc

>          U __vfprintf_chk
>          U __vsnprintf_chk
>          U __vsprintf_chk

there are many _chk functions for _FORTIFY_SOURCE, musl may provide
these eventually, until then you can add your own chk.o with dummy
implementations (possibly with the safety checks i omit here):

int __vfprintf_chk(FILE *f, int flag, const char *fmt, va_list ap)
{
	return vfprintf(f, fmt, ap);
}
int __vsnprintf_chk(char *s, size_t n, int flag, size_t size, const char *fmt, va_list ap)
{
	return vsnprintf(s, n, fmt, ap);
}
int __vsprintf_chk(char *s, int flag, size_t size, const char *fmt, va_list ap)
{
	return vsprintf(s, fmt, ap);
}

>          U __sysv_signal

use signal

> So, I am wondering if the musl library could at some point provide
> these routines to enable users to do what I am trying to do.

compiling with glibc headers and then linking to musl
cannot be supported in general, because of ABI compat issues

(eg glibc headers define PTHREAD_*_INITIALIZER macros that hardcode
glibc internal ABI at compile time that does not match musl)

if you are sure you don't have such ABI breakage (see glibc
vs musl differences on the wiki) then you may get away by
adding a glibc-compat.o to your musl build

> 
> Any possibility of that?
> 
> Thanks,
> Dave