Anhad Singh
22bbdb025c
From man dlopen(3) > According to the ISO C standard, casting between function > pointers and 'void *', as done above, produces undefined results. > POSIX.1-2001 and POSIX.1-2008 accepted this state of affairs and > proposed the following workaround: > > *(void **) (&cosine) = dlsym(handle, "cos"); > > This (clumsy) cast conforms with the ISO C standard and will > avoid any compiler warnings. > > The 2013 Technical Corrigendum 1 to POSIX.1-2008 improved matters > by requiring that conforming implementations support casting > 'void *' to a function pointer. Nevertheless, some compilers > (e.g., gcc with the '-pedantic' option) may complain about the > cast used in this program. Signed-off-by: Anhad Singh <andypython@protonmail.com>
112 lines
2.1 KiB
C
112 lines
2.1 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <dlfcn.h>
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int add(int a, int b)
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{
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return a + b;
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}
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void test_dlopen_null()
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{
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void* handle = dlopen(NULL, RTLD_LAZY);
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if (!handle) {
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printf("dlopen(NULL) failed\n");
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exit(1);
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}
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int (*f)(int, int);
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*(void **)(&f) = dlsym(handle, "add");
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if (!f) {
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printf("dlsym(handle, add) failed\n");
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exit(2);
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}
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int a = 22;
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int b = 33;
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printf("add(%d, %d) = %d\n", a, b, f(a, b));
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dlclose(handle);
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}
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void test_dlopen_libc()
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{
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void* handle = dlopen("libc.so.6", RTLD_LAZY);
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if (!handle) {
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printf("dlopen(libc.so.6) failed\n");
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exit(1);
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}
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int (*f)(const char*);
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*(void **)(&f) = dlsym(handle, "puts");
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if (!f) {
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printf("dlsym(handle, puts) failed\n");
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exit(2);
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}
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f("puts from dlopened libc");
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dlclose(handle);
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}
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void test_dlsym_function()
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{
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void* handle = dlopen("sharedlib.so", RTLD_LAZY);
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if (!handle) {
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printf("dlopen(sharedlib.so) failed\n");
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exit(1);
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}
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void (*f)();
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*(void **)(&f) = dlsym(handle, "print");
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if (!f) {
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printf("dlsym(handle, print) failed\n");
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exit(2);
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}
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f();
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dlclose(handle);
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}
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void test_dlsym_global_var()
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{
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void* handle = dlopen("sharedlib.so", RTLD_LAZY);
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if (!handle) {
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printf("dlopen(sharedlib.so) failed\n");
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exit(1);
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}
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int* global_var = dlsym(handle, "global_var");
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if (!global_var) {
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printf("dlsym(handle, global_var) failed\n");
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exit(2);
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}
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printf("main: global_var == %d\n", *global_var);
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dlclose(handle);
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}
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void test_dlsym_tls_var()
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{
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void* handle = dlopen("sharedlib.so", RTLD_LAZY);
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if (!handle) {
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printf("dlopen(sharedlib.so) failed\n");
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exit(1);
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}
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int* tls_var = dlsym(handle, "tls_var");
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if (!tls_var) {
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printf("dlsym(handle, tls_var) failed\n");
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exit(2);
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}
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printf("main: tls_var == %d\n", *tls_var);
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dlclose(handle);
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}
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int main()
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{
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test_dlopen_null();
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test_dlopen_libc();
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test_dlsym_function();
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test_dlsym_global_var();
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test_dlsym_tls_var();
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}
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