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Date: Fri, 14 Mar 2014 12:47:20 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Cc: Support at Gcom <support@...m.com>
Subject: Re: Static linking of musl with code compiled using GNU
header files
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
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