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內(nèi)存泄漏是指由于疏忽或錯(cuò)誤造成程序未能釋放已經(jīng)不再使用的內(nèi)存。內(nèi)存泄漏并非指內(nèi)存在物理上的消失，而是應(yīng)用程序分配某段內(nèi)存后，由于設(shè)計(jì)錯(cuò)誤，導(dǎo)致在釋放該段內(nèi)存之前就失去了對(duì)該段內(nèi)存的控制，從而造成了內(nèi)存的浪費(fèi)。

我們平時(shí)開發(fā)過程中不可避免的會(huì)遇到內(nèi)存泄漏問題，你是如何排查的呢？估計(jì)你是使用下面這幾個(gè)工具吧？

valgrind
mtrace
dmalloc
ccmalloc
memwatch
debug_new

這里程序喵向大家推薦新的一個(gè)排查內(nèi)存泄漏的工具：AddressSanitizer(ASan)，該工具為gcc自帶，4.8以上版本都可以使用，支持Linux、OS、Android等多種平臺(tái)，不止可以檢測(cè)內(nèi)存泄漏，它其實(shí)是一個(gè)內(nèi)存錯(cuò)誤檢測(cè)工具，可以檢測(cè)的問題有：

內(nèi)存泄漏
堆棧和全局內(nèi)存越界訪問
free后繼續(xù)使用
局部?jī)?nèi)存被外層使用
Initialization order bugs(中文不知道怎么翻譯才好，后面有代碼舉例，重要)

使用方法直接看我下面的代碼：

檢測(cè)內(nèi)存泄漏

內(nèi)存泄漏代碼：

#include 
void func1() { malloc(7); }
void func2() { malloc(5); }
int main() {   func1();   func2();   return 0;}

編譯and輸出：

g++ -fsanitize=address -g test_leak.cc && ./a.out
===================================================================103==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 7 byte(s) in 1 object(s) allocated from:   #0 0x7f95b231eb40 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdeb40)   #1 0x7f95b36007f7 in func1() /home/wangzhiqiang/test/test_leak.cc:3   #2 0x7f95b3600814 in main /home/wangzhiqiang/test/test_leak.cc:8   #3 0x7f95b1e61b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
Direct leak of 5 byte(s) in 1 object(s) allocated from:   #0 0x7f95b231eb40 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdeb40)   #1 0x7f95b3600808 in func2() /home/wangzhiqiang/test/test_leak.cc:5   #2 0x7f95b3600819 in main /home/wangzhiqiang/test/test_leak.cc:9   #3 0x7f95b1e61b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: 12 byte(s) leaked in 2 allocation(s).

編譯方式很簡(jiǎn)單，只需要添加-fsanitize=address -g就可以檢測(cè)出具體產(chǎn)生內(nèi)存泄漏的位置以及泄漏空間的大小。

檢測(cè)堆棧內(nèi)存越界訪問

示例：

#include 
int main() {   int *array = new int[100];   array[0] = 0;   int res = array[100];  // out of bounds   delete[] array;   return res;}

編譯and輸出：

g++ -fsanitize=address -g test_leak.cc && ./a.out   ===================================================================110==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6140000001d0 at pc 0x7f0e06400d2e bp 0x7ffff5963f10 sp 0x7ffff5963f00READ of size 4 at 0x6140000001d0 thread T0   #0 0x7f0e06400d2d in main /home/wangzhiqiang/test/test_leak.cc:6   #1 0x7f0e048d1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)   #2 0x7f0e06400bb9 in _start (/mnt/d/wzq/wzq/util/test/a.out+0xbb9)
0x6140000001d0 is located 0 bytes to the right of 400-byte region [0x614000000040,0x6140000001d0)allocated by thread T0 here:   #0 0x7f0e05120608 in operator new[](unsigned long) (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xe0608)   #1 0x7f0e06400cab in main /home/wangzhiqiang/test/test_leak.cc:4   #2 0x7f0e048d1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: heap-buffer-overflow /home/wangzhiqiang/test/test_leak.cc:6 in mainShadow bytes around the buggy address: 0x0c287fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c287fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c287fff8000: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00 0x0c287fff8010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c287fff8020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x0c287fff8030: 00 00 00 00 00 00 00 00 00 00[fa]fa fa fa fa fa 0x0c287fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c287fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c287fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c287fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c287fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa faShadow byte legend (one shadow byte represents 8 application bytes): Addressable:           00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone:       fa Freed heap region:       fd Stack left redzone:      f1 Stack mid redzone:       f2 Stack right redzone:     f3 Stack after return:      f5 Stack use after scope:   f8 Global redzone:          f9 Global init order:       f6 Poisoned by user:        f7 Container overflow:      fc Array cookie:            ac Intra object redzone:    bb ASan internal:           fe Left alloca redzone:     ca Right alloca redzone:    cb==110==ABORTING

可以方便定位到堆棧內(nèi)存越界訪問的錯(cuò)誤。

全局內(nèi)存越界訪問：

示例：

#include 
int global_array[100] = {0};
int main() {   int res = global_array[100];  // out of bounds   return 0;}

編譯and輸出：

g++ -fsanitize=address -g test_leak.cc && ./a.out===================================================================116==ERROR: AddressSanitizer: global-buffer-overflow on address 0x7f42e6e02310 at pc 0x7f42e6c00c84 bp 0x7fffdda52780 sp 0x7fffdda52770READ of size 4 at 0x7f42e6e02310 thread T0   #0 0x7f42e6c00c83 in main /home/wangzhiqiang/test/test_leak.cc:6   #1 0x7f42e50d1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)   #2 0x7f42e6c00b69 in _start (/mnt/d/wzq/wzq/util/test/a.out+0xb69)
0x7f42e6e02310 is located 0 bytes to the right of global variable 'global_array' defined in 'test_leak.cc:3:5' (0x7f42e6e02180) of size 400SUMMARY: AddressSanitizer: global-buffer-overflow /home/wangzhiqiang/test/test_leak.cc:6 in mainShadow bytes around the buggy address: 0x0fe8dcdb8410: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb8420: 00 00 00 00 00 00 00 00 01 f9 f9 f9 f9 f9 f9 f9 0x0fe8dcdb8430: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb8440: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb8450: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x0fe8dcdb8460: 00 00[f9]f9 f9 f9 f9 f9 00 00 00 00 00 00 00 00 0x0fe8dcdb8470: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb8480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb8490: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb84a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0fe8dcdb84b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00Shadow byte legend (one shadow byte represents 8 application bytes): Addressable:           00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone:       fa Freed heap region:       fd Stack left redzone:      f1 Stack mid redzone:       f2 Stack right redzone:     f3 Stack after return:      f5 Stack use after scope:   f8 Global redzone:          f9 Global init order:       f6 Poisoned by user:        f7 Container overflow:      fc Array cookie:            ac Intra object redzone:    bb ASan internal:           fe Left alloca redzone:     ca Right alloca redzone:    cb==116==ABORTING

局部?jī)?nèi)存被外層使用

示例：

#include 
volatile int *p = 0;
int main() {{   int x = 0;   p = &x;} *p = 5; return 0;}

編譯and輸出：

g++ -fsanitize=address -g test_leak.cc && ./a.out===================================================================243==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffce12a4b0 at pc 0x7f3993e00e7e bp 0x7fffce12a480 sp 0x7fffce12a470WRITE of size 4 at 0x7fffce12a4b0 thread T0  #0 0x7f3993e00e7d in main /home/wangzhiqiang/test/test_leak.cc:10  #1 0x7f39922d1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)  #2 0x7f3993e00c89 in _start (/mnt/d/wzq/wzq/util/test/a.out+0xc89)
Address 0x7fffce12a4b0 is located in stack of thread T0 at offset 32 in frame  #0 0x7f3993e00d79 in main /home/wangzhiqiang/test/test_leak.cc:5
This frame has 1 object(s):  [32, 36) 'x' <== Memory access at offset 32 is inside this variableHINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext    (longjmp and C++ exceptions *are* supported)SUMMARY: AddressSanitizer: stack-use-after-scope /home/wangzhiqiang/test/test_leak.cc:10 in mainShadow bytes around the buggy address:0x100079c1d440: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d450: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d460: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d470: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x100079c1d490: 00 00 f1 f1 f1 f1[f8]f2 f2 f2 00 00 00 00 00 000x100079c1d4a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d4b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d4c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d4d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 000x100079c1d4e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00Shadow byte legend (one shadow byte represents 8 application bytes):Addressable:           00Partially addressable: 01 02 03 04 05 06 07Heap left redzone:       faFreed heap region:       fdStack left redzone:     f1Stack mid redzone:       f2Stack right redzone:     f3Stack after return:     f5Stack use after scope:   f8Global redzone:         f9Global init order:       f6Poisoned by user:       f7Container overflow:     fcArray cookie:           acIntra object redzone:   bbASan internal:           feLeft alloca redzone:     caRight alloca redzone:   cb==243==ABORTING

free后被使用

示例：

#include 
int main() {    int *array = new int[100];    delete[] array;    int a = array[0];  // error    return 0;}

編譯and輸出：

g++ -fsanitize=address -g test_leak.cc && ./a.out===================================================================282==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000040 at pc 0x7f209fa00caa bp 0x7ffff2a15020 sp 0x7ffff2a15010READ of size 4 at 0x614000000040 thread T0    #0 0x7f209fa00ca9 in main /home/wangzhiqiang/test/test_leak.cc:6    #1 0x7f209ded1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)    #2 0x7f209fa00b69 in _start (/mnt/d/wzq/wzq/util/test/a.out+0xb69)
0x614000000040 is located 0 bytes inside of 400-byte region [0x614000000040,0x6140000001d0)freed by thread T0 here:    #0 0x7f209e721480 in operator delete[](void*) (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xe1480)    #1 0x7f209fa00c72 in main /home/wangzhiqiang/test/test_leak.cc:5    #2 0x7f209ded1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
previously allocated by thread T0 here:    #0 0x7f209e720608 in operator new[](unsigned long) (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xe0608)    #1 0x7f209fa00c5b in main /home/wangzhiqiang/test/test_leak.cc:4    #2 0x7f209ded1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: heap-use-after-free /home/wangzhiqiang/test/test_leak.cc:6 in mainShadow bytes around the buggy address:  0x0c287fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0c287fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0c287fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0c287fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0c287fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=>0x0c287fff8000: fa fa fa fa fa fa fa fa[fd]fd fd fd fd fd fd fd  0x0c287fff8010: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd  0x0c287fff8020: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd  0x0c287fff8030: fd fd fd fd fd fd fd fd fd fd fa fa fa fa fa fa  0x0c287fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa  0x0c287fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa faShadow byte legend (one shadow byte represents 8 application bytes):  Addressable:           00  Partially addressable: 01 02 03 04 05 06 07  Heap left redzone:       fa  Freed heap region:       fd  Stack left redzone:      f1  Stack mid redzone:       f2  Stack right redzone:     f3  Stack after return:      f5  Stack use after scope:   f8  Global redzone:          f9  Global init order:       f6  Poisoned by user:        f7  Container overflow:      fc  Array cookie:            ac  Intra object redzone:    bb  ASan internal:           fe  Left alloca redzone:     ca  Right alloca redzone:    cb==282==ABORTING

Initialization order bugs

示例，這里有兩個(gè)文件：

// test_memory1.cc#include 
extern int extern_global;int read_extern_global() { return extern_global; }
int x = read_extern_global() + 1;
int main() {    printf("%d\n", x);    return 0;}

// test_memory2.cc
int foo() { return 123; }int extern_global = foo();

第一種編譯方式輸出如下：

g++ test_memory1.cc test_memory2.cc && ./a.out1

第二種編譯方式輸出如下：

g++ test_memory2.cc test_memory1.cc && ./a.out124

這種問題我們平時(shí)編程過程中可以都不會(huì)太注意，然而通過ASan可以檢測(cè)出這種潛在的bug：

編譯and輸出：

g++ -fsanitize=address -g test_memory1.cc test_memory2.cc
ASAN_OPTIONS=check_initialization_order=true:strict_init_order=true ./a.out===================================================================419==ERROR: AddressSanitizer: initialization-order-fiasco on address 0x7f46c20021a0 at pc 0x7f46c1e00c28 bp 0x7fffe423d920 sp 0x7fffe423d910READ of size 4 at 0x7f46c20021a0 thread T0    #0 0x7f46c1e00c27 in read_extern_global() /home/wangzhiqiang/test/test_memory1.cc:3    #1 0x7f46c1e00cb3 in __static_initialization_and_destruction_0 /home/wangzhiqiang/test/test_memory1.cc:4    #2 0x7f46c1e00d0a in _GLOBAL__sub_I__Z18read_extern_globalv /home/wangzhiqiang/test/test_memory1.cc:8    #3 0x7f46c1e00e5c in __libc_csu_init (/mnt/d/wzq/wzq/util/test/a.out+0xe5c)    #4 0x7f46c0461b27 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b27)    #5 0x7f46c1e00b09 in _start (/mnt/d/wzq/wzq/util/test/a.out+0xb09)
0x7f46c20021a0 is located 0 bytes inside of global variable 'extern_global' defined in 'test_memory2.cc:2:5' (0x7f46c20021a0) of size 4  registered at:    #0 0x7f46c08764a8  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x364a8)    #1 0x7f46c1e00e0b in _GLOBAL__sub_I_00099_1__Z3foov (/mnt/d/wzq/wzq/util/test/a.out+0xe0b)    #2 0x7f46c1e00e5c in __libc_csu_init (/mnt/d/wzq/wzq/util/test/a.out+0xe5c)
SUMMARY: AddressSanitizer: initialization-order-fiasco /home/wangzhiqiang/test/test_memory1.cc:3 in read_extern_global()Shadow bytes around the buggy address:  0x0fe9583f83e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f83f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8410: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8420: 00 00 00 00 00 00 00 00 04 f9 f9 f9 f9 f9 f9 f9=>0x0fe9583f8430: 00 00 00 00[f6]f6 f6 f6 f6 f6 f6 f6 00 00 00 00  0x0fe9583f8440: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8450: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8460: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8470: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  0x0fe9583f8480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00Shadow byte legend (one shadow byte represents 8 application bytes):  Addressable:           00  Partially addressable: 01 02 03 04 05 06 07  Heap left redzone:       fa  Freed heap region:       fd  Stack left redzone:      f1  Stack mid redzone:       f2  Stack right redzone:     f3  Stack after return:      f5  Stack use after scope:   f8  Global redzone:          f9  Global init order:       f6  Poisoned by user:        f7  Container overflow:      fc  Array cookie:            ac  Intra object redzone:    bb  ASan internal:           fe  Left alloca redzone:     ca  Right alloca redzone:    cb==419==ABORTING

注意：這里在運(yùn)行程序前需要添加環(huán)境變量：

ASAN_OPTIONS=check_initialization_order=true:strict_init_order=true

小總結(jié)

ASan是個(gè)很好的檢測(cè)內(nèi)存問題的工具，不需要配置環(huán)境，使用還方便，編譯時(shí)只需要-fsanitize=address -g就可以，運(yùn)行程序時(shí)候可以選擇添加對(duì)應(yīng)的ASAN_OPTIONS環(huán)境變量就可以檢測(cè)出很多內(nèi)存問題。它的錯(cuò)誤信息也很有用，明確指出當(dāng)前是什么類型的內(nèi)存錯(cuò)誤，如：

detected memory leaks
heap-buffer-overflow
stack-buffer-overflow
global-buffer-overflow
heap-use-after-free
initialization-order-fiasco

具體可以看google的官方文檔：https://github.com/google/sanitizers/wiki/AddressSanitizer

Linux如何調(diào)試內(nèi)存泄漏