8
我想通過LD_PRELOAD
替換原來的mmap()
系統調用在預先識別的fd上,以便調用它的進程可以讀取先前創建的共享內存對象另一個過程與boost::interprocess
。一切都很順利,除非我最終嘗試讀取mmap內存。在這種情況下,第一個進程會因分段錯誤而中止。原因是什麼?我不需要在共享內存對象上寫入權限。mmap()與LD_PRELOAD和boost :: interprocess不起作用
這是在預加載庫中的代碼:
void *mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset) {
static void* (*o_mmap) (void *, size_t, int, int, int, off_t) =
o_mmap = (void*(*)(void *, size_t, int, int, int, off_t)) dlsym(RTLD_NEXT, "mmap");
if (!o_mmap)
std::cout << "mmap() preload failed\n";
if (fd != my_fd)
return (*o_mmap)(start, length, prot, flags, fd, offset);
interprocess::shared_memory_object shm (interprocess::open_only, "obj", interprocess::read_only);
interprocess::mapped_region region(shm, interprocess::read_only, 0, length, start);
std::cout << "mmap() overridden. addr =" << region.get_address() << " length: " << region.get_size() << " start: " << start << "\n";
return region.get_address();
}
程序創建共享存儲器對象的代碼是:
//Create a shared memory object.
shared_memory_object shm (create_only, "obj", read_write);
//Set size
shm.truncate(1000);
//Map the whole shared memory in this process
mapped_region region(shm, read_write);
//Write all the memory to 1
std::memset(region.get_address(), 1, region.get_size());
該方案的代碼(其出現segfaults)試圖讀取上面的共享內存是:
int fd = open(my_file, O_RDONLY);
void* addr = mmap(0, 1000, PROT_READ, MAP_SHARED, fd, 0); // Okay
//Check that memory was initialized to 1
char *mem = static_cast<char*>(addr);
for(std::size_t i = 0; i < 1000; ++i)
if(*mem++ != 1) // SEGFAULT!
return 1; //Error checking memory
你可以顯示你的'mmap'替換代碼嗎?它可能有問題。 – 2013-02-08 18:07:47
我會盡快。 – Martin 2013-02-08 18:08:39
是否確定要用自己的實現來替換流程中的每個單個mmap()調用?如果您使用的是LD_PRELOAD技巧,那麼會發生這種情況... – 2013-02-08 18:11:33