c - 通过 LD_PRELOAD 替换 `malloc`、`calloc`、`realloc` 和 `free` 时出现分段错误
问题描述
背景
我正在尝试通过环境变量替换malloc(3)/// calloc(3)。我尝试使用静态链接的自定义函数，它们运行良好。realloc(3)free(3)LD_PRELOAD
但是，当我将它作为共享库附加到 时LD_PRELOAD，它总是会导致段错误。
关于功能的简短技术说明
- 我使用 Linux x86-64
mmap(2)和munmap(2)系统调用malloc(3)和free(3). - 这
calloc(3)只是对malloc(3)乘法溢出检查的调用。 realloc(3)调用，然后malloc(3)将旧数据复制到新分配的内存并取消映射旧内存。
问题
- 我的方法有什么问题，以至于它总是导致段错误？
- 我该如何调试它（gdb 和 valgrind 也有段错误）？
- 我在这里错过了什么？
笔记
我完全意识到mmap每次malloc通话都使用是一个坏主意，尤其是在性能方面。我只想知道为什么我的方法不起作用。
输出
ammarfaizi2@integral:~$ gcc -shared mem.c -O3 -o my_mem.so
ammarfaizi2@integral:~$ LD_PRELOAD=$(pwd)/my_mem.so ls
Segmentation fault (core dumped)
ammarfaizi2@integral:~$ LD_PRELOAD=$(pwd)/my_mem.so cat
Segmentation fault (core dumped)
ammarfaizi2@integral:~$ LD_PRELOAD=$(pwd)/my_mem.so w
Segmentation fault (core dumped)
ammarfaizi2@integral:~$ LD_PRELOAD=$(pwd)/my_mem.so gdb ls
Segmentation fault (core dumped)
ammarfaizi2@integral:~$ LD_PRELOAD=$(pwd)/my_mem.so valgrind ls
Segmentation fault (core dumped)
ammarfaizi2@integral:~$
glibc 版本
ammarfaizi2@integral:~$ /lib/x86_64-linux-gnu/libc.so.6
GNU C Library (Ubuntu GLIBC 2.33-0ubuntu2) release release version 2.33.
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 10.2.1 20210130.
libc ABIs: UNIQUE IFUNC ABSOLUTE
For bug reporting instructions, please see:
<https://bugs.launchpad.net/ubuntu/+source/glibc/+bugs>.
ammarfaizi2@integral:~$
代码 mem.c
#include <errno.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>
#include <string.h>
static inline void *my_mmap(void *addr, size_t length, int prot, int flags,
int fd, off_t offset)
{
void *ret;
register int _flags asm("r10") = flags;
register int _fd asm("r8") = fd;
register off_t _offset asm("r9") = offset;
asm volatile(
"syscall"
: "=a"(ret)
: "a"(9), "D"(addr), "S"(length), "d"(prot),
"r"(_flags), "r"(_fd), "r"(_offset)
: "memory", "r11", "rcx"
);
return ret;
}
static inline int my_munmap(void *addr, size_t length)
{
int ret;
asm volatile(
"syscall"
: "=a"(ret)
: "a"(11), "D"(addr), "S"(length)
: "memory", "r11", "rcx"
);
return ret;
}
#define unlikely(EXPR) __builtin_expect(EXPR, 0)
void * __attribute__((noinline)) malloc(size_t len)
{
void *start_map;
uintptr_t user_ptr, cmperr;
size_t add_req = 0;
add_req += sizeof(size_t);
add_req += sizeof(uint8_t);
add_req += 0x1full;
start_map = my_mmap(NULL, add_req + len, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
cmperr = 0xffffffffffffff00ull;
if (unlikely(((uintptr_t)start_map & cmperr) == cmperr)) {
errno = ENOMEM;
return NULL;
}
/* Align 32-byte and take space to save the length and diff */
user_ptr = ((uintptr_t)start_map + add_req) & ~0x1full;
*(size_t *)(user_ptr - 8) = len;
*(uint8_t *)(user_ptr - 9) = (uint8_t)(user_ptr - (uintptr_t)start_map);
return (void *)user_ptr;
}
void free(void *__user_ptr)
{
size_t len;
uint8_t diff;
uintptr_t user_ptr = (uintptr_t)__user_ptr;
len = *(size_t *)(user_ptr - 8);
diff = *(uint8_t *)(user_ptr - 9);
my_munmap((void *)(user_ptr - diff), len);
}
void *realloc(void *__user_ptr, size_t new_len)
{
void *new_mem;
size_t len;
uint8_t diff;
uintptr_t user_ptr = (uintptr_t)__user_ptr;
len = *(size_t *)(user_ptr - 8);
diff = *(uint8_t *)(user_ptr - 9);
new_mem = malloc(new_len);
if (unlikely(new_mem == NULL))
return NULL;
memcpy(new_mem, __user_ptr, (new_len < len) ? new_len : len);
my_munmap((void *)(user_ptr - diff), len);
return new_mem;
}
void *calloc(size_t nmemb, size_t len)
{
size_t x = nmemb * len;
if (unlikely(nmemb != 0 && x / nmemb != len)) {
errno = EOVERFLOW;
return NULL;
}
return malloc(x);
}
// #include <stdio.h>
// int main(void)
// {
// char *test = malloc(1);
// for (size_t i = 2; i <= (1024 * 1024); i++) {
// test = realloc(test, i);
// memset(test, 'q', i);
// }
// free(test);
// }
重新编译-Wall -Wextra -ggdb3并strace输出
ammarfaizi2@integral:~$
ammarfaizi2@integral:~$ gcc -Wall -Wextra -ggdb3 -shared mem.c -O3 -o my_mem.so
ammarfaizi2@integral:~$ strace -tf /usr/bin/env LD_PRELOAD=$(pwd)/my_mem.so ls
12:59:15 execve("/usr/bin/env", ["/usr/bin/env", "LD_PRELOAD=/home/ammarfaizi2/my_"..., "ls"], 0x7ffd2d6ee188 /* 34 vars */) = 0
12:59:15 brk(NULL) = 0x565552193000
12:59:15 arch_prctl(0x3001 /* ARCH_??? */, 0x7ffd13017120) = -1 EINVAL (Invalid argument)
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=74118, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 74118, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7facba2ba000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\206\2\0\0\0\0\0"..., 832) = 832
12:59:15 pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
12:59:15 pread64(3, "\4\0\0\0 \0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0"..., 48, 848) = 48
12:59:15 pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\30\355\366\266\203\242\371v\214\300\356\234\306J\346\373"..., 68, 896) = 68
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=1983576, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7facba2b8000
12:59:15 pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
12:59:15 mmap(NULL, 2012056, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7facba0cc000
12:59:15 mmap(0x7facba0f2000, 1486848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7facba0f2000
12:59:15 mmap(0x7facba25d000, 311296, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x191000) = 0x7facba25d000
12:59:15 mmap(0x7facba2a9000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1dc000) = 0x7facba2a9000
12:59:15 mmap(0x7facba2af000, 33688, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7facba2af000
12:59:15 close(3) = 0
12:59:15 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7facba0ca000
12:59:15 arch_prctl(ARCH_SET_FS, 0x7facba2b95c0) = 0
12:59:15 mprotect(0x7facba2a9000, 12288, PROT_READ) = 0
12:59:15 mprotect(0x565550cb5000, 4096, PROT_READ) = 0
12:59:15 mprotect(0x7facba2ff000, 8192, PROT_READ) = 0
12:59:15 munmap(0x7facba2ba000, 74118) = 0
12:59:15 brk(NULL) = 0x565552193000
12:59:15 brk(0x5655521b4000) = 0x5655521b4000
12:59:15 openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=3041456, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 3041456, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7facb9de3000
12:59:15 close(3) = 0
12:59:15 execve("/home/ammarfaizi2/.local/bin/ls", ["ls"], 0x565552194550 /* 35 vars */) = -1 ENOENT (No such file or directory)
12:59:15 execve("/usr/local/sbin/ls", ["ls"], 0x565552194550 /* 35 vars */) = -1 ENOENT (No such file or directory)
12:59:15 execve("/usr/local/bin/ls", ["ls"], 0x565552194550 /* 35 vars */) = -1 ENOENT (No such file or directory)
12:59:15 execve("/usr/sbin/ls", ["ls"], 0x565552194550 /* 35 vars */) = -1 ENOENT (No such file or directory)
12:59:15 execve("/usr/bin/ls", ["ls"], 0x565552194550 /* 35 vars */) = 0
12:59:15 brk(NULL) = 0x557f8624b000
12:59:15 arch_prctl(0x3001 /* ARCH_??? */, 0x7fff39dc1a30) = -1 EINVAL (Invalid argument)
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/home/ammarfaizi2/my_mem.so", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\20\0\0\0\0\0\0"..., 832) = 832
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0700, st_size=58768, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa7daa68000
12:59:15 mmap(NULL, 16448, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa7daa63000
12:59:15 mmap(0x7fa7daa64000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1000) = 0x7fa7daa64000
12:59:15 mmap(0x7fa7daa65000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fa7daa65000
12:59:15 mmap(0x7fa7daa66000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fa7daa66000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=74118, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 74118, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa7daa50000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libselinux.so.1", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0 p\0\0\0\0\0\0"..., 832) = 832
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=167352, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 178664, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa7daa24000
12:59:15 mmap(0x7fa7daa2a000, 106496, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7fa7daa2a000
12:59:15 mmap(0x7fa7daa44000, 32768, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x20000) = 0x7fa7daa44000
12:59:15 mmap(0x7fa7daa4c000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x27000) = 0x7fa7daa4c000
12:59:15 mmap(0x7fa7daa4e000, 6632, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa7daa4e000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\206\2\0\0\0\0\0"..., 832) = 832
12:59:15 pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
12:59:15 pread64(3, "\4\0\0\0 \0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0"..., 48, 848) = 48
12:59:15 pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\30\355\366\266\203\242\371v\214\300\356\234\306J\346\373"..., 68, 896) = 68
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=1983576, ...}, AT_EMPTY_PATH) = 0
12:59:15 pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
12:59:15 mmap(NULL, 2012056, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa7da838000
12:59:15 mmap(0x7fa7da85e000, 1486848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7fa7da85e000
12:59:15 mmap(0x7fa7da9c9000, 311296, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x191000) = 0x7fa7da9c9000
12:59:15 mmap(0x7fa7daa15000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1dc000) = 0x7fa7daa15000
12:59:15 mmap(0x7fa7daa1b000, 33688, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa7daa1b000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libpcre2-8.so.0", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340\"\0\0\0\0\0\0"..., 832) = 832
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=617160, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 619304, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa7da7a0000
12:59:15 mmap(0x7fa7da7a2000, 438272, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fa7da7a2000
12:59:15 mmap(0x7fa7da80d000, 167936, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6d000) = 0x7fa7da80d000
12:59:15 mmap(0x7fa7da836000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x95000) = 0x7fa7da836000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0 \"\0\0\0\0\0\0"..., 832) = 832
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=22912, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 24848, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa7da799000
12:59:15 mmap(0x7fa7da79b000, 8192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fa7da79b000
12:59:15 mmap(0x7fa7da79d000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x7fa7da79d000
12:59:15 mmap(0x7fa7da79e000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x7fa7da79e000
12:59:15 close(3) = 0
12:59:15 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
12:59:15 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
12:59:15 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\200\0\0\0\0\0\0"..., 832) = 832
12:59:15 pread64(3, "\4\0\0\0 \0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0"..., 48, 792) = 48
12:59:15 pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0a7\363\352;k|\2228\244\6\253\346\2569\312"..., 68, 840) = 68
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=150456, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 136208, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa7da777000
12:59:15 mmap(0x7fa7da77e000, 65536, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x7000) = 0x7fa7da77e000
12:59:15 mmap(0x7fa7da78e000, 20480, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x7fa7da78e000
12:59:15 mmap(0x7fa7da793000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b000) = 0x7fa7da793000
12:59:15 mmap(0x7fa7da795000, 13328, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa7da795000
12:59:15 close(3) = 0
12:59:15 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa7da775000
12:59:15 mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa7da772000
12:59:15 arch_prctl(ARCH_SET_FS, 0x7fa7da772800) = 0
12:59:15 mprotect(0x7fa7daa15000, 12288, PROT_READ) = 0
12:59:15 mprotect(0x7fa7da793000, 4096, PROT_READ) = 0
12:59:15 mprotect(0x7fa7da79e000, 4096, PROT_READ) = 0
12:59:15 mprotect(0x7fa7da836000, 4096, PROT_READ) = 0
12:59:15 mprotect(0x7fa7daa4c000, 4096, PROT_READ) = 0
12:59:15 mprotect(0x7fa7daa66000, 4096, PROT_READ) = 0
12:59:15 mprotect(0x557f842f9000, 8192, PROT_READ) = 0
12:59:15 mprotect(0x7fa7daa9c000, 8192, PROT_READ) = 0
12:59:15 munmap(0x7fa7daa50000, 74118) = 0
12:59:15 set_tid_address(0x7fa7da772ad0) = 1639769
12:59:15 set_robust_list(0x7fa7da772ae0, 24) = 0
12:59:15 rt_sigaction(SIGRTMIN, {sa_handler=0x7fa7da77eb70, sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7fa7da78b160}, NULL, 8) = 0
12:59:15 rt_sigaction(SIGRT_1, {sa_handler=0x7fa7da77ec10, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_SIGINFO, sa_restorer=0x7fa7da78b160}, NULL, 8) = 0
12:59:15 rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
12:59:15 prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
12:59:15 statfs("/sys/fs/selinux", 0x7fff39dc1a00) = -1 ENOENT (No such file or directory)
12:59:15 statfs("/selinux", 0x7fff39dc1a00) = -1 ENOENT (No such file or directory)
12:59:15 mmap(NULL, 512, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa7daa9b000
12:59:15 openat(AT_FDCWD, "/proc/filesystems", O_RDONLY|O_CLOEXEC) = 3
12:59:15 mmap(NULL, 160, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa7daa62000
12:59:15 newfstatat(3, "", {st_mode=S_IFREG|0444, st_size=0, ...}, AT_EMPTY_PATH) = 0
12:59:15 mmap(NULL, 1064, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa7daa61000
12:59:15 read(3, "nodev\tsysfs\nnodev\ttmpfs\nnodev\tbd"..., 1024) = 410
12:59:15 read(3, "", 1024) = 0
12:59:15 munmap(0x7fa7daa62000, 120) = 0
12:59:15 close(3) = 0
12:59:15 munmap(0x7fa7daa61000, 1024) = 0
12:59:15 munmap(0x7fa7daa9b000, 472) = 0
12:59:15 --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0xfffffffffffffff7} ---
12:59:16 +++ killed by SIGSEGV (core dumped) +++
Segmentation fault (core dumped)
ammarfaizi2@integral:~$
使用 /usr/bin/env 后的 Valgrind 输出
ammarfaizi2@integral:~$ valgrind --track-origins=yes --leak-check=full --show-leak-kinds=all /usr/bin/env LD_PRELOAD=$(pwd)/my_mem.so ls
==1640100== Memcheck, a memory error detector
==1640100== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1640100== Using Valgrind-3.17.0 and LibVEX; rerun with -h for copyright info
==1640100== Command: /usr/bin/env LD_PRELOAD=/home/ammarfaizi2/my_mem.so ls
==1640100==
Segmentation fault (core dumped)
ammarfaizi2@integral:~$
解决方案
我已经调试了核心文件并修复了崩溃，对于free函数，您需要检查参数是否为nullptr，因为realloc我们需要处理__user_ptr的nullptr也是。
void free(void *__user_ptr) {
if (!__user_ptr) return;
// ...
}
void *realloc(void *__user_ptr, size_t new_len) {
void *new_mem;
size_t len;
uint8_t diff;
uintptr_t user_ptr = (uintptr_t)__user_ptr;
new_mem = malloc(new_len);
if (!__user_ptr) return new_mem;
// ....
}
我在编写内存分配器库方面有一些经验。在调试过程中，我发现一些旧的 c 程序使用reallocasmalloc与nullptr参数，这很奇怪但完全有效，请参考手册页
realloc() 函数将 ptr 指向的内存块的大小更改为 size 字节。内容将在从区域开始到新旧大小的最小值的范围内保持不变。如果新大小大于旧大小，则不会初始化添加的内存。如果 ptr 为 NULL，则对于所有 size 值，调用等效于 malloc(size)；如果 size 等于 0，并且 ptr 不为 NULL，则调用等效于 free(ptr)。除非 ptr 为 NULL，否则它一定是由先前对 malloc()、calloc() 或 realloc() 的调用返回的。如果指向的区域被移动，则执行 free(ptr)。
顺便说一句，我看到您尝试包装syscallfor mmapand munmap，我建议我们将它们替换为https://github.com/linux-on-ibm-z/linux-syscall-support，这是一个生产级别包装库并被广泛使用。我认为我们应该尽可能少写代码来减少潜在的错误。
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