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

[Rich Felker <dalias@aerifal.cx>]

On Fri, Mar 14, 2014 at 10:47:31AM -0500, David Grothe wrote:
> Hello,
> 
> 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
> this and link my-huge-program.o with musl libc.a I get the following
> list of unresolved externals:
> 
>          U __divdi3
>          w __fini_array_end
>          w __fini_array_start
>          U __moddi3
>          U __sysv_signal
>          U __udivdi3
>          U __umoddi3
>          U __vfprintf_chk
>          U __vsnprintf_chk
>          U __vsprintf_chk
>          U __sysv_signal

The presence of __divdi3, __moddi3, __udivdi3, and __umoddi3 in this
list indicates that you're missing libgcc.a. If you're using
-nostdlib, you need to manually add libgcc back to the linker command
line. __fini_array_start and __fini_array_end are provided by the
linker and are not necessary unless your code has global destructors
that the compiler is implementing via fini_array (this is why they're
weak).

The rest are __sysv_signal and __*_chk. The former looks suspicious: I
really doubt you _want_ to be using the sysv version of signal(); it
probably got pulled in by glibc's headers due to bad feature test
macros or something. As for the latter, these come from
_FORTIFY_SOURCE which musl does not yet support.

> 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.
> 
> Any possibility of that?

Likely for at least some of them, but not right away. And there are at
least a few features (e.g. pthread cancellation) that will never work
this way.

BTW is there a reason you want to use glibc's headers with musl? If
your program is having lots of build errors with musl's, it's probably
indicative of problems you should fix; some of these problems may
become problems with future glibc versions too.

Rich