Created
March 7, 2019 19:13
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Wrapping library functions using -Wl,--wrap=symbol
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| CC := gcc | |
| CFLAGS += -Wall -Wextra -std=c99 | |
| LDLIBS += -lpthread | |
| all: test_wrap | |
| test_wrap: LDFLAGS += -Wl,--wrap=pthread_create -Wl,--wrap=pthread_join | |
| test_wrap: test_wrap.c wrap.c | |
| clean: | |
| rm -rf test_wrap | |
| .PHONY: all clean |
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| #include <assert.h> | |
| #include <pthread.h> | |
| #include <stdlib.h> | |
| unsigned int num_threads; | |
| static void *thread_entry_fn(void *arg) | |
| { | |
| (void)arg; | |
| return NULL; | |
| } | |
| int main(int argc, char *argv[]) | |
| { | |
| unsigned int n = argc > 1 && atoi(argv[1]) >= 0 ? atoi(argv[1]) : 4; | |
| pthread_t *threads = malloc(n * sizeof(pthread_t)); | |
| if (!threads) return EXIT_FAILURE; | |
| for (unsigned int i = 0; i < n; i++) { | |
| pthread_create(&threads[i], NULL, thread_entry_fn, NULL); | |
| } | |
| assert(num_threads == n); | |
| for (unsigned int i = 0; i < n; i++) { | |
| pthread_join(threads[i], NULL); | |
| } | |
| assert(num_threads == 0); | |
| free(threads); | |
| return 0; | |
| } |
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| #include <pthread.h> | |
| extern unsigned int num_threads; | |
| // From the docs: | |
| // Any undefined reference to `symbol` will be resolved to `__wrap_symbol`. Any | |
| // undefined reference to `__real_symbol` will be resolved to `symbol`. This | |
| // can be used to provide a wrapper for a system function. The wrapper function | |
| // should be called `__wrap_symbol`. If it wishes to call the system function, | |
| // it should call `__real_symbol`. | |
| extern int __real_pthread_create(pthread_t *, const pthread_attr_t *, void *(*)(void *), void *); | |
| extern int __real_pthread_join(pthread_t, void **); | |
| int __wrap_pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void *), void *arg) | |
| { | |
| num_threads++; | |
| return __real_pthread_create(thread, attr, start_routine, arg); | |
| } | |
| int __wrap_pthread_join(pthread_t thread, void **retval) | |
| { | |
| num_threads--; | |
| return __real_pthread_join(thread, retval); | |
| } |
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