I am creating a shared library using c++ -shared (which is gcc running on x86_64). I can't manage to strip my problem down to a minimal test case, but the issue I'm having is that I am creating a .so out of a bunch of .o files. One of those .o files exports a symbol (nm shows 'D') that I want exported from the .so. Others of the .o's require that symbol (nm shows 'U'). As a result, the linker makes that symbol local in the resulting .so (nm shows 'd').
If I eliminate the requiring .o's from the command line, the .so does export the symbol. So it seems like the linker is deciding that since other .o's used to build the .so require the symbol, that it must only be needed by those .o's and it needn't be exported for real.
When I try to construct a minimal test case, it doesn't work this way; the symbol is always exported whether or not I add in a .o that requires it.
My full command line is:
c++ -fno-rtti -fno-exceptions -Wall -Wpointer-arith -Woverloaded-virtual -Wsynth -Wno-ctor-dtor-privacy -Wno-non-virtual-dtor -Wcast-align -Wno-invalid-offsetof -Wno-variadic-macros -pedantic -Wno-long-long -gdwarf-2 -fno-strict-aliasing -pthread -pipe -DDEBUG -D_DEBUG -DDEBUG_sfink -DTRACING -gdwarf-2 -fPIC -shared -Wl,-z,defs -Wl,-h,libmozjs.so -o libmozjs.so jsapi.o jsarena.o jsarray.o jsatom.o jsbool.o jscntxt.o jsdate.o jsdbgapi.o jsdhash.o jsdtoa.o jsemit.o jsexn.o jsfun.o jsgc.o jsgcchunk.o jshash.o jsinterp.o jsinvoke.o jsiter.o jslock.o jslog2.o jsmath.o jsnativestack.o jsnum.o jsobj.o json.o jsopcode.o jsparse.o jsproxy.o jsprf.o jspropertycache.o jspropertytree.o jsregexp.o jsscan.o jsscope.o jsscript.o jsstr.o jstask.o jstypedarray.o jsutil.o jswrapper.o jsxdrapi.o jsxml.o prmjtime.o jsdtracef.o jstracer.o Assembler.o Allocator.o CodeAlloc.o Containers.o Fragmento.o LIR.o njconfig.o RegAlloc.o avmplus.o NativeX64.o jsbuiltins.o VMPI.o CTypes.o Library.o mozjs-dtrace.o -lpthread -Wl,-rpath-link,/bin -Wl,-rpath-link,/lib -Wl,--whole-archive ctypes/libffi/.libs/libffi.a -Wl,--no-whole-archive -L/home/sfink/moz-central/obj-dtrace/dist/lib -lplds4 -lplc4 -lnspr4 -lpthread -ldl -ldl -lm -lm -ldl
I get the same behavior with the core command that this invokes (I also manually pruned out some irrelevant flags):
/usr/bin/ld --no-add-needed --eh-frame-hdr --build-id -m elf_x86_64 --hash-style=gnu -shared -o libmozjs.so /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../lib64/crti.o /usr/lib/gcc/x86_64-redhat-linux/4.4.4/crtbeginS.o -L/usr/lib/gcc/x86_64-redhat-linux/4.4.4 -L/usr/lib/gcc/x86_64-redhat-linux/4.4.4 -L/usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../.. jsapi.o jsarena.o jsarray.o jsatom.o jsbool.o jscntxt.o jsdate.o jsdbgapi.o jsdhash.o jsdtoa.o jsemit.o jsexn.o jsfun.o jsgc.o jsgcchunk.o jshash.o jsinterp.o jsinvoke.o jsiter.o jslock.o jslog2.o jsmath.o jsnativestack.o jsnum.o jsobj.o json.o jsopcode.o jsparse.o jsproxy.o jsprf.o jspropertycache.o jspropertytree.o jsregexp.o jsscan.o jsscope.o jsscript.o jsstr.o jstask.o jstypedarray.o jsutil.o jswrapper.o jsxdrapi.o jsxml.o prmjtime.o jsdtracef.o jstracer.o Assembler.o Allocator.o CodeAlloc.o Containers.o Fragmento.o LIR.o njconfig.o RegAlloc.o avmplus.o NativeX64.o jsbuiltins.o VMPI.o mozjs-dtrace.o -lnspr4 -lstdc++ -lm -lgcc_s -lpthread -lc -lgcc_s /usr/lib/gcc/x86_64-redhat-linux/4.4.4/crtendS.o /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../lib64/crtn.o
Update: probably more importantly, those symbols are in a different section, and have hidden visibility. Using objcopy to make them global doesn't help. I don't know what the rules are for which sections to use for what.