Static library link issue with Mac OS X: symbol(s)

问题:

I'm trying to generate a static library and link it with an execution binary.

This is a library function:

#include <stdio.h>

int hello() {
    return 10;
}

With these commands, I could get a static library.

gcc -c io.c 
ar -crv libio.a io.o

With lip -info, I checked it is x86_64 architecture.

ar> lipo -info libio.a 
input file libio.a is not a fat file
Non-fat file: libio.a is architecture: x86_64

This is the main function that uses the library.

#include <stdio.h>
extern int hello();

int main(int argc, char *argv[]) {
    printf("%d", hello());
}

However, when I link the object with the static library, I have errors.

gcc main.c -lio -o main -L.

Error messages are:

ld: warning: ignoring file ./libio.a, file was built for archive which is not the architecture being linked (x86_64): ./libio.a
Undefined symbols for architecture x86_64:
  "_hello", referenced from:
      _main in main-2c41a0.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I use the ar as in /bin/ar, and Mac OS X is 10.10.2 with clang-602.0.53.

ar> clang -v
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix

What might be wrong?

回答1:

The library should have generated with libtool -static.

gcc -c io.c 
libtool -static -o libio.a io.o
gcc main.c -lio -o main -L.
main

Returns

10

ar> lipo -info libio.a 
input file libio.a is not a fat file
Non-fat file: libio.a is architecture: x86_64

ar> file libio.a 
libio.a: current ar archive

ar> nm libio.a 

io.o:
0000000000000000 T _hello

Hints from this page.

回答2:

From hacking CMake generate make file (CMakeFiles/test.dir/link.txt), the ar in /usr/local/ar which is used in default does not seem to be working correctly.

This is the content of the link.txt.

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar qc libtest.a  CMakeFiles/test.dir/test.c.o   
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib libtest.a

From the script, /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar is the one that I had to use.

smcho@macho ar> ls -alF /usr/bin/ar
-rwxr-xr-x  1 root  wheel  18160 Oct 17 18:49 /usr/bin/ar*
smcho@macho ar> ls -alF /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar 
-rwxr-xr-x  1 root  wheel  33472 Oct 29 16:36 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar*

Likewise, the ranlib that should be used is /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib not the default one.

smcho@macho ar> ls -alF `which ar`
-rwxr-xr-x  1 root  wheel  18160 Oct 17 18:49 /usr/bin/ar*
smcho@macho ar> ls -alF /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib
lrwxr-xr-x  1 root  wheel  7 Nov 10 21:10 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib@ -> libtool

Other than that -qc option needed to be used (from the cmake generated script)

 -c      Whenever an archive is created, an informational message to that
         effect is written to standard error.  If the -c option is speci-
         fied, ar creates the archive silently. 
 -q      (Quickly) append the specified files to the archive.  If the ar-
         chive does not exist a new archive file is created.  Much faster
         than the -r option, when creating a large archive piece-by-piece,
         as no checking is done to see if the files already exist in the
         archive.

These are commands for getting correct library file:

clang -c hellolib.cpp -o hellolib.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar -qc libhello.a hellolib.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib libhello.a

The usage is:

clang usehello.cpp -lhello -L.

nm and lipo show the correct library file information:

smcho@macho ar> nm libhello.a 
libhello.a(hellolib.o):
0000000000000000 T __Z3addii
smcho@macho ar> lipo -info libhello.a 
input file libhello.a is not a fat file
Non-fat file: libhello.a is architecture: x86_64