DynamicLinkerTests.mk

all: test-dl test-lrpath1 test-lrpath2 test-lsoname1 test-lsoname2 test-lsymver1 test-lsymver2

.SECONDARY:

clean:
	rm -rf 1 2 libuse* libdef* test-* foo*.o

test-dl: test.c
	gcc $< -ldl -o $@

# -fuse-ld=gold should only be necessary on Ubuntu 14.04
test-l%: test.c libuse%.so
	gcc -DWITH_LINK='"$*"' -fuse-ld=gold -L. $< -luse$* -ldl -o $@

libuserpath%.so: %/libdefrpath.so
	gcc -fPIC -shared -DWITH_VERSION=$* -L$* -Wl,-rpath,./$* usever.c -ldefrpath -o $@

1 2:
	mkdir -p $@

%/libdefrpath.so: foo%.o %
	gcc -shared $< -o $@

libusesoname%.so: libdefsoname.so.%
	ln -sf $< libdefsoname.so
	gcc -fPIC -shared -DWITH_VERSION=$* -L. usever.c -ldefsoname -o $@

libdefsoname.so.%: foo%.o
	gcc -shared -Wl,-h,$@ $< -o $@

libusesymver%.so: libdefsymver.so
	gcc -fPIC -shared -DWITH_VERSION=$* -DWITH_SYMVER='"$*"' -L. usever.c -ldefsymver -o $@

libdefsymver.so: foo1.symver.o foo2.symver.o symver.map
	gcc -shared -Wl,-z,muldefs -Wl,--version-script,symver.map foo1.symver.o foo2.symver.o -o $@

foo%.o: foo%.c
	gcc -fPIC -c $< -o $@

foo%.symver.o: foo%.c
	gcc -fPIC -DSYMVER -c $< -o $@

foo1.c

#include <stdio.h>

#ifdef SYMVER
__asm__(".symver foo,foo@VERS_1.1");
#endif
void foo() {
	puts("Hello from foo 1");
}

foo2.c

#include <stdio.h>

#ifdef SYMVER
__asm__(".symver foo,foo@VERS_1.2");
#endif
void foo() {
	puts("Hello from foo 2");
}

symver.map

VERS_1.1 { foo; };
VERS_1.2 { foo; };

test.c

#define _GNU_SOURCE

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <dlfcn.h>

#ifdef WITH_LINK
extern void use_foo();
#endif

static void call_foo(const char* arg) {
#ifdef WITH_LINK
	if (0==strcmp(arg,"lt")) {
		puts("call_foo using link-time linkage:");
		use_foo();
	} else
#endif
	if (0==strncmp(arg,"dl,",3)) {
		printf("call_foo using %s:\n",arg);
		arg+=3;

		int flags=RTLD_LOCAL;
		if (0==strncmp(arg,"lazy,",5)) {
			arg+=5;
			flags|=RTLD_LAZY;
		} else if (0==strncmp(arg,"now,",4)) {
			arg+=4;
			flags|=RTLD_NOW;
		} else {
			puts("Must specify lazy or now!");
			return;
		}

		void* lib;
		int pseudo_lib=1;
		
		if (0==strcmp(arg,"default")) {
			lib=RTLD_DEFAULT;
		} else if (0==strcmp(arg,"next")) {
			lib=RTLD_NEXT;
		} else {
			lib=dlopen(arg,flags);
			pseudo_lib=0;
		}
		
		if (pseudo_lib || lib) {
			void* fun=dlsym(lib,"use_foo");
			if (fun)
				((void(*)())fun)();
			else
				puts("Error in dlsym");
			if (!pseudo_lib) dlclose(lib);
		} else {
			puts("Error in dlopen");
		}
	} else {
		printf("Unknown call style: %s\n",arg);
	}
}

void main(int argc, char** argv) {
	if (argc==1) {
		printf("Usage: %s "
#ifdef WITH_LINK
		"lt|"
#endif
		"dl,(lazy|now),(default|next|libname.so) ...\n",argv[0]);
		return;
	}
	printf("WITH_LINK: %s\n",
#ifdef WITH_LINK
		WITH_LINK	
#else
		"(undefined)"
#endif
	);
	printf("LD_LIBRARY_PATH: %s\n",getenv("LD_LIBRARY_PATH"));
	int i;
	for (i=1;i<argc;i++) call_foo(argv[i]);
	
	FILE* fp=fopen("/proc/self/maps","r");
	if (fp) {
		char buf[4096];
		size_t bytes_read;
		while (!feof(fp)) {
			bytes_read=fread(buf,1,sizeof(buf),fp);
			fwrite(buf,1,bytes_read,stdout);
		}
	}
}

usever.c

#include <stdio.h>

#ifdef WITH_SYMVER
__asm__(".symver foo,foo@VERS_1." WITH_SYMVER);
#endif
extern void foo();

void use_foo() {
	printf("Hello from use_foo WITH_VERSION=%d\n",WITH_VERSION);
	foo();
}