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简介
AddressSanitizer 是 Google 开发的一款用于检测内存拜访谬误的工具，用于解决 use-after-free 和内存透露的相干问题。它内置在 GCC 版本 >= 4.8 中，实用于 C 和 C++ 代码。AddressSanitizer 可在应用运行时检测跟踪内存调配，这意味着必须应用 AddressSanitizer 构建代码能力利用它的性能。
因为内存透露会减少程序应用的总内存，所以当不再须要内存时，正确开释内存很重要。或者对于小程序，失落几个字节仿佛没什么大不了的，然而对于应用大量内存的长时间运行的程序，防止内存透露变得越来越重要。如果程序不再须要它时，无奈开释应用的内存，很可能会耗尽内存，从而导致应用程序提前终止。AddressSanitizer 的呈现，就能够帮忙检测这些内存透露。
此外，AddressSanitizer 能够检测 use-after-free 谬误。当程序尝试读取或写入已被开释的内存时，会产生开释后应用谬误。这是未定义的行为，可能会导致数据损坏、后果不正确，甚至程序解体。
如果检测到谬误，程序将向 stderr 打印谬误音讯，并以非零退出代码退出，若是应用 AddressSanitizer，那么它在第一个检测到的谬误时就退出。
留神
- ASan 应用本人的内存分配器（malloc, free 等）
- ASan 应用大量虚拟地址空间（x86_64 Linux 上为 20T）
应用
-fsanitize=address 标记用于通知编译器，将增加 AddressSanitizer，对应用调试符号编译代码很有帮忙。如果存在调试符号，须要 AddressSanitizer 打印行号，那么请增加 -g 标记。此外，如果您发现堆栈跟踪看起来不太正确，应用 -fno-omit-frame-pointer 就能够显示更具体的调用栈信息，合并成一条命令生成可执行文件：
gcc main.cpp -o main -g -fsanitize=address此段代码为 Bash
或者，分成独自的编译和链接阶段：
gcc -c main.cpp -fsanitize=address -g` -fno-omit-frame-pointer
gcc main.o -o main -fsanitize=address此段代码为 Bash
请留神，编译和链接步骤都须要 -fsanitize=address 标记。如果构建零碎更简单，将这些标记放在 CXXFLAGS 和 LDFLAGS 环境变量中。
性能 AddressSanitizer 比进行相似剖析的工具（如 valgrind）快得多。为了取得较好的性能能够应用 -O1 或更高的优化。
然而，如果感觉 AddressSanitizer 对某些代码来说太慢，就能够应用编译器标记来禁用它，以用于特定性能。有助于在代码的较冷局部应用 AddressSanitizer，同时手动审核热门路。
跳过剖析函数的编译器指令是 __attribute__((no_sanitize_address)。
谬误类型
1. Use after free
内存开释后还被应用。
int main(int argc, char **argv) {int *array = new int[100];
delete [] array;
return array[argc]; // BOOM
}此段代码为 C
===================================================================3262==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000044 at pc 0x55c005566d89 bp 0x7fffc64dc040 sp 0x7fffc64dc030READ of size 4 at 0x614000000044 thread T0
#0 0x55c005566d88 in main /root/study/cmakeutils/src/main.cpp:6
#1 0x7fdb76b17082 in __libc_start_main ../csu/libc-start.c:308
#2 0x55c005566c4d in _start (/root/study/cmakeutils/build/main+0xdc4d)
0x614000000044 is located 4 bytes inside of 400-byte region [0x614000000040,0x6140000001d0)freed by thread T0 here:
#0 0x7fdb77396b97 in operator delete[](void*) ../../../../src/libsanitizer/asan/asan_new_delete.cpp:163
#1 0x55c005566d3c in main /root/study/cmakeutils/src/main.cpp:5
#2 0x7fdb76b17082 in __libc_start_main ../csu/libc-start.c:308
previously allocated by thread T0 here:
#0 0x7fdb77396097 in operator new[](unsigned long) ../../../../src/libsanitizer/asan/asan_new_delete.cpp:102
#1 0x55c005566d25 in main /root/study/cmakeutils/src/main.cpp:4
#2 0x7fdb76b17082 in __libc_start_main ../csu/libc-start.c:308
...此段代码为 Bash
第 4 行显示了 READ（内存读取）的地位，return array[argc]；
第 10 行显示了 freed（内存开释）的地位，delete [] array；
第 16 行显示了 allocate（内存申请）的地位，int *array = new int[100]。
2. Heap buffer overflow
申请了堆空间，数组下标超出申请范畴。
int main(int argc, char **argv) {int *array = new int[100];
array[0] = 0;
int res = array[argc + 100]; // BOOM
delete [] array;
return res;}此段代码为 C++ 语言
===================================================================3407==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6140000001d4 at pc 0x55753d9b4dbb bp 0x7ffe7d1e77e0 sp 0x7ffe7d1e77d0READ of size 4 at 0x6140000001d4 thread T0
#0 0x55753d9b4dba in main /root/study/cmakeutils/src/main.cpp:6
#1 0x7f9f5683b082 in __libc_start_main ../csu/libc-start.c:308
#2 0x55753d9b4c4d in _start (/root/study/cmakeutils/build/main+0xdc4d)
0x6140000001d4 is located 4 bytes to the right of 400-byte region [0x614000000040,0x6140000001d0)allocated by thread T0 here:
#0 0x7f9f570ba097 in operator new[](unsigned long) ../../../../src/libsanitizer/asan/asan_new_delete.cpp:102
#1 0x55753d9b4d25 in main /root/study/cmakeutils/src/main.cpp:4
#2 0x7f9f5683b082 in __libc_start_main ../csu/libc-start.c:308
...此段代码为 Bash
第 4 行显示了 READ 的地位，int res = array[argc + 100]；
第 11 行显示了 allocate 的地位，int *array = new int[100]；
因为这里 argc + 100 >= 100，array 下标为 0-99，所以呈现谬误。
3. Stack buffer overflow
局部变量，数组下标超出范围。
int main(int argc, char **argv) {int stack_array[100];
stack_array[1] = 0;
return stack_array[argc + 100]; // BOOM
}此段代码为 C++ 语言
===================================================================3529==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff4c128d44 at pc 0x55ccafbf0e13 bp 0x7fff4c128b60 sp 0x7fff4c128b50READ of size 4 at 0x7fff4c128d44 thread T0
#0 0x55ccafbf0e12 in main /root/study/cmakeutils/src/main.cpp:6
#1 0x7f624dc97082 in __libc_start_main ../csu/libc-start.c:308
#2 0x55ccafbf0c0d in _start (/root/study/cmakeutils/build/main+0xdc0d)
Address 0x7fff4c128d44 is located in stack of thread T0 at offset 452 in frame
#0 0x55ccafbf0cd8 in main /root/study/cmakeutils/src/main.cpp:3
This frame has 1 object(s):
[48, 448) 'stack_array' (line 4) <== Memory access at offset 452 overflows this variableHINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
(longjmp and C++ exceptions *are* supported)
...此段代码为 Bash
第 4 行显示了 READ 的地位，return stack_array[argc + 100]；
第 12 行显示了变量的地位，int stack_array[100]。
4. Global buffer overflow
全局变量，数组下标超出范围。
int global_array[100] = {-1};
int main(int argc, char **argv) {return global_array[argc + 100]; // BOOM
}此段代码为 C++
===================================================================3653==ERROR: AddressSanitizer: global-buffer-overflow on address 0x55b61f0391b4 at pc 0x55b61efd7d2b bp 0x7fff8bc1cbd0 sp 0x7fff8bc1cbc0READ of size 4 at 0x55b61f0391b4 thread T0
#0 0x55b61efd7d2a in main /root/study/cmakeutils/src/main.cpp:5
#1 0x7f0637717082 in __libc_start_main ../csu/libc-start.c:308
#2 0x55b61efd7c0d in _start (/root/study/cmakeutils/build/main+0xdc0d)
0x55b61f0391b4 is located 4 bytes to the right of global variable 'global_array' defined in '/root/study/cmakeutils/src/main.cpp:3:5' (0x55b61f039020) of size 400
...此段代码为 Bash
第 4 行显示了 READ 的地位，return global_array[argc + 100]；
第 8 行显示了全局变量的地位，int global_array[100] = {-1}。
5. Use after return
指针指向了一个函数的局部变量，函数返回后局部变量生效，但应用了该指针。
// 默认不检测该项，可设置 ASAN_OPTIONS=detect_stack_use_after_return= 1 开启检测 int* ptr;
__attribute__((noinline)) void FunctionThatEscapesLocalObject() {int local[100];
ptr = &local[0];}
int main(int argc, char** argv) {FunctionThatEscapesLocalObject();
return ptr[argc];
}此段代码为 C++
===================================================================3811==ERROR: AddressSanitizer: stack-use-after-return on address 0x7fd77133e234 at pc 0x555fb157be71 bp 0x7fffdb165710 sp 0x7fffdb165700READ of size 4 at 0x7fd77133e234 thread T0
#0 0x555fb157be70 in main /root/study/cmakeutils/src/main.cpp:11
#1 0x7fd7746db082 in __libc_start_main ../csu/libc-start.c:308
#2 0x555fb157bc0d in _start (/root/study/cmakeutils/build/main+0xdc0d)
Address 0x7fd77133e234 is located in stack of thread T0 at offset 52 in frame
#0 0x555fb157bcd8 in FunctionThatEscapesLocalObject() /root/study/cmakeutils/src/main.cpp:4
This frame has 1 object(s):
[48, 448) 'local' (line 5) <== Memory access at offset 52 is inside this variableHINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
(longjmp and C++ exceptions *are* supported)
...此段代码为 Bash
第 4 行显示 READ 地位，return ptr[argc]；
第 12 行显示变量地位，int local[100]；
这里 ptr 指向了一个局部变量的地址 ptr = &local[0]，而后在 FunctionThatEscapesLocalObject 函数返回后，拜访该地址。
6. Use after scope
指针指向了一个范畴变量，该范畴退出后变量生效，但应用了该指针。
volatile int *p = 0;
int main() {
{
int x = 0;
p = &x;
}
*p = 5;
return 0;
}此段代码为 C++
===================================================================3922==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7ffecd93f880 at pc 0x5616c0570de0 bp 0x7ffecd93f850 sp 0x7ffecd93f840WRITE of size 4 at 0x7ffecd93f880 thread T0
#0 0x5616c0570ddf in main /root/study/cmakeutils/src/main.cpp:10
#1 0x7f2ccf8c3082 in __libc_start_main ../csu/libc-start.c:308
#2 0x5616c0570c0d in _start (/root/study/cmakeutils/build/main+0xdc0d)
Address 0x7ffecd93f880 is located in stack of thread T0 at offset 32 in frame
#0 0x5616c0570cd8 in main /root/study/cmakeutils/src/main.cpp:5
This frame has 1 object(s):
[32, 36) 'x' (line 7) <== Memory access at offset 32 is inside this variableHINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
(longjmp and C++ exceptions *are* supported)
...此段代码为 Bash
第 4 行显示了 WRITE（写内存）的地位，*p = 5；
第 12 行显示了变量地位，int x = 0；这里 x 的作用域在 {} 外部，因为 *p = 5 在 {} 外，所以 x 生效了。
7. Memory leaks
内存泄露，申请了未开释。
void *p;
int main() {p = malloc(7);
p = 0; // The memory is leaked here.
return 0
}此段代码为 C++
===================================================================4076==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 7 byte(s) in 1 object(s) allocated from: #0 0x7f799fcff527 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
#1 0x55a10f15acfa in main /root/study/cmakeutils/src/main.cpp:6
#2 0x7f799f482082 in __libc_start_main ../csu/libc-start.c:308
SUMMARY: AddressSanitizer: 7 byte(s) leaked in 1 allocation(s).此段代码为 Visual Basic
第 6 行显示了内存申请的地位，p = malloc(7)；
第 9 行显示了总的内存泄露。
总结
编写内存平安的代码，是一个长期比拟艰难的问题，因为 C/C++ 不是一门内存平安的语言，所以此类问题会常常遇到。AddressSanitizer 的呈现，使得相干 bug 的定位和解决问题的难度都失去了降落，并放慢我的项目的进度。