I'm pretty sure I'm running into a pr-msvc-support-specific problem but I'm
still learning about libtool so...
I'm trying to get rid of unresolved externs when linked an executable
against a libtool shared library compiled with msvc. The unresolved externs
are global variables. The code in question yet another getopt
implementation. The variables are declared and defined like this:
<getopt.h>
extern UTL_EXPORT int opterr;
extern UTL_EXPORT int optind;
extern UTL_EXPORT int optopt;
extern UTL_EXPORT int optreset;
extern UTL_EXPORT char *optarg;
<getopt_long.c>
int opterr = 1;
int optind = 1;
int optopt = '?';
int optreset;
char *optarg;
UTL_EXPORT becomes __declspec(dllexport) when compiling the shared lib,
__declspec(dllimport) when compiling the executable that uses it.
What's interesting is that I only get unresolved externs for the initialized
variables:
utils-test.obj : error LNK2001: unresolved external symbol _optopt
utils-test.obj : error LNK2001: unresolved external symbol _optind
utils-test.obj : error LNK2001: unresolved external symbol _opterr
Snippets from dumpbin -symbols on the getopt_long.obj look like this:
COFF SYMBOL TABLE
000 006DC627 ABS notype Static | @comp.id
001 00000001 ABS notype Static | @feat.00
002 00000000 SECT1 notype Static | .drectve
Section length C9, #relocs 0, #linenums 0, checksum 0
004 00000000 SECT2 notype Static | .debug$S
Section length 1EEC, #relocs 5B, #linenums 0, checksum 0
006 00000000 SECT3 notype Static | .bss
Section length 7, #relocs 0, #linenums 0, checksum 0
008 00000000 SECT3 notype Static | $SG6258
009 00000004 UNDEF notype External | _optarg
00A 00000004 UNDEF notype External | _optreset
00B 00000000 SECT4 notype Static | .data
Section length 44, #relocs 1, #linenums 0, checksum 2C7EE1AD
00D 00000000 SECT4 notype External | _opterr
00E 00000004 SECT4 notype External | _optind
00F 00000008 SECT4 notype External | _optopt
010 0000000C SECT4 notype Static | _place
Note that the unitialized variables are marked as "UNDEF" whereas optopt,
optind and optopt are marked as "SECT4".
After a bit of digging, I have a feeling that the place to fix this is the
source file that puts this in the generated libtool script:
# Take the output of nm and produce a listing of raw symbols and C names.
global_symbol_pipe="gawk ' {last_section=section; section=\$ 3};
/Section length .*#relocs.*(pick any)/{hide[last_section]=1}; \$
0!~/External *\\|/{next}; / 0+ UNDEF /{next}; / UNDEF
\\([^|]\\)*()/{next}; {if(hide[section]) next}; {f=0}; \$
0~/\\(\\).*\\|/{f=1}; {printf f ? \"T \" : \"D \"}; {split(\$ 0, a,
/\\||\\r/); split(a[2], s)}; s[1]~/^...@?]/{print s[1], s[1]; next};
s[1]~prfx {split(s[1],t,\"@\"); print t[1], substr(t[1],length(prfx))} '
prfx=^_"
My libtool/awk skills are not where they need to be to fix this. My
understanding of symbol resolution/linking in general is not where it needs
to be to even know if pulling in everything marked "External" but not
necessarily "UNDEF" is the right thing to do.
I could (obviously) use a hand here.
Thanks for your help.
$ cl
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.762 for
80x86
$ link
Microsoft (R) Incremental Linker Version 8.00.50727.762
$ libtool --version
libtool (GNU libtool 1.3107 2009-03-20) 2.2.7a
relevant args to configure (run from msys):
$ ../configure CC=cl CXX=cl CPPFLAGS=-D_CRT_SECURE_NO_WARNINGS CFLAGS=-W3
-Zc:wchar_t- -Zi -Od -MDd CXXFLAGS=-W3 -EHsc -Zc:wchar_t- -Zi -Od -MDd
LD=link LDFLAGS=-DEBUG NM=dumpbin -symbols AR=lib STRIP=: RANLIB=:
-DB
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