mallocをフックしてメモリ使用量を測る

#define _GNU_SOURCE
#include <dlfcn.h>
#include <string.h>
#include <stdio.h>

static size_t max_usage;
static size_t cur_usage;

static void *(*orig_malloc)(size_t);
static void (*orig_free)(void *);
static void *(*orig_realloc)(void *, size_t);

__attribute__((constructor)) void initialize(void) {
    orig_malloc = dlsym(RTLD_NEXT, "malloc");
    orig_free = dlsym(RTLD_NEXT, "free");
    orig_realloc = dlsym(RTLD_NEXT, "realloc");
}

extern char *__progname;

__attribute__((destructor)) void print_stat(void) {
    size_t result = max_usage;
    fprintf(stderr, "%s: max memory usage: %zu\n", __progname, result);
}

void *malloc(size_t size) {
    void *ptr = orig_malloc(size + sizeof(size_t));
    if (ptr == NULL) {
        return NULL;
    }
    memcpy(ptr, &size, sizeof(size_t));
    cur_usage += size;
    if (cur_usage > max_usage) {
        max_usage = cur_usage;
    }
    return (void *)((unsigned char *)ptr + sizeof(size_t));
}

void *calloc(size_t nmemb, size_t size) {
    void *ptr = malloc(nmemb * size);
    if (ptr != NULL) {
        memset(ptr, 0, size * nmemb);
    }
    return ptr;
}

void free(void *ptr) {
    if (ptr == NULL) {
        return;
    }
    void *head = (void *)((unsigned char *)ptr - sizeof(size_t));
    size_t size;
    memcpy(&size, head, sizeof(size_t));
    cur_usage -= size;
    orig_free(head);
}

void *realloc(void *ptr, size_t size) {
    size_t old_size = 0;
    void *result;
    if (ptr != NULL) {
        void *head = (void *)((unsigned char *)ptr - sizeof(size_t));
        memcpy(&old_size, head, sizeof(size_t));
        result = orig_realloc(head, size + sizeof(size_t));
    } else {
        result = orig_realloc(ptr, size + sizeof(size_t));
    }
    if (result != NULL) {
        cur_usage -= old_size;
        cur_usage += size;
        if (cur_usage > max_usage) {
            max_usage = cur_usage;
        }
        memcpy(result, &size, sizeof(size));
        return (void *)((unsigned char *)result + sizeof(size_t));
    }
    return NULL;
}

void *reallocarray(void *ptr, size_t nmemb, size_t size) {
    return realloc(ptr, nmemb * size);
}

$ gcc -shared -fPIC -ldl -o libmh.so mh.c

$ LD_PRELOAD=/path/to/libmh.so hogehoge