Hook mmap

hook_mmap.c

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

#define TRAP_MMAP_LIMIT (4 << 20)

#define DECLARE_HOOK(mmap) \
    void *mmap(void *addr, size_t, int, int, int, loff_t) __attribute__((weak,alias("hook_"#mmap)));\
    typedef void *(*mmap_ptr_t)(void *, size_t, int, int, int, loff_t); 


#define DEFINE_HOOK(mmap)                                               \
void *hook_##mmap(void *addr, size_t length, int prot, int flags, int fd, loff_t offset) { \
    printf("Inside %s\n", __FUNCTION__);                                \
    mmap_ptr_t orig_mmap = (mmap_ptr_t)dlsym(RTLD_NEXT, #mmap);               \
    if(length > TRAP_MMAP_LIMIT) {                                              \
        printf("Large mmap\n");                                        \
    }                                                                   \
    return orig_mmap(addr, length, prot, flags, fd, offset);            \
}

DECLARE_HOOK(mmap)
DEFINE_HOOK(mmap)

Makefile

## LD_PRELOAD=$PATH/libhookmmap.so $PROG

CC := gcc
SRCS := hook_mmap.c
OBJS := $(SRCS:%.c=%.o)
TARGETS = libhookmmap.so
DEBUG_FLAGS = -g
CFLAGS = -Wall -fPIC -shared
LD_LIBS = -ldl

all: $(TARGETS)

libhookmmap.so: $(OBJS)
	$(CC) -shared -o $@ $^ $(DEBUG_FLAGS) $(LD_LIBS)

%.o:%.c
	$(CC) -c $(CFLAGS) -o $@ $<

clean:
	rm $(TARGETS); rm $(OBJS)