5
我有以下非常簡單的C程序（test.c）「無效寫」：意外的valgrind當fstack檢查用於
int f(int i)
{
return i;
}
int main(int argC, char* argV[])
{
int x = f(12);
return 1;
}
我已經做了一些試驗用的valgrind，在兩次與-fstack-check編譯器標誌打不同的系統。
測試在Debian 8.6與gcc 4.9.2和valgrind 3.10.0。
沒有-fstack-check：
$ gcc test.c -o test
$ valgrind ./test
==103703== Memcheck, a memory error detector
==103703== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==103703== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==103703== Command: ./test
==103703==
==103703==
==103703== HEAP SUMMARY:
==103703== in use at exit: 0 bytes in 0 blocks
==103703== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==103703==
==103703== All heap blocks were freed -- no leaks are possible
==103703==
==103703== For counts of detected and suppressed errors, rerun with: -v
==103703== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1 from 1)
隨着-fstack-check：
$ gcc -fstack-check test.c -o test
$ valgrind ./test
==103726== Memcheck, a memory error detector
==103726== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==103726== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==103726== Command: ./test
==103726==
==103726==
==103726== HEAP SUMMARY:
==103726== in use at exit: 0 bytes in 0 blocks
==103726== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==103726==
==103726== All heap blocks were freed -- no leaks are possible
==103726==
==103726== For counts of detected and suppressed errors, rerun with: -v
==103726== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1 from 1)
測試中的CentOS 6.6用gcc 4.4.7和3.8.1 Valgrind的完成：
沒有-fstack-check：
$ gcc test.c -o test
$ valgrind ./test
==16390== Memcheck, a memory error detector
==16390== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==16390== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==16390== Command: ./test
==16390==
==16390==
==16390== HEAP SUMMARY:
==16390== in use at exit: 0 bytes in 0 blocks
==16390== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==16390==
==16390== All heap blocks were freed -- no leaks are possible
==16390==
==16390== For counts of detected and suppressed errors, rerun with: -v
==16390== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 6)
隨着-fstack-check：
$ gcc -fstack-check test.c -o test
$ valgrind ./test
==16441== Memcheck, a memory error detector
==16441== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==16441== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==16441== Command: ./test
==16441==
==16441== Invalid write of size 8
==16441== at 0x400497: main (in /home/fermin/valgrindtest/test)
==16441== Address 0x7feffd058 is not stack'd, malloc'd or (recently) free'd
==16441==
==16441==
==16441== Process terminating with default action of signal 11 (SIGSEGV)
==16441== Access not within mapped region at address 0x7FEFFD058
==16441== at 0x400497: main (in /home/fermin/valgrindtest/test)
==16441== If you believe this happened as a result of a stack
==16441== overflow in your program's main thread (unlikely but
==16441== possible), you can try to increase the size of the
==16441== main thread stack using the --main-stacksize= flag.
==16441== The main thread stack size used in this run was 10485760.
==16441==
==16441== HEAP SUMMARY:
==16441== in use at exit: 0 bytes in 0 blocks
==16441== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==16441==
==16441== All heap blocks were freed -- no leaks are possible
==16441==
==16441== For counts of detected and suppressed errors, rerun with: -v
==16441== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 6)
在這種情況下，此外，該程序與段錯誤結束。
綜上所述，而Debian的一切似乎是確定與-fstack-check，在CentOS的我收到一個「無效寫」錯誤，我無法解釋給我的程序代碼。
閱讀有關the -fstack-check flag也許是錯誤跟蹤是由於堆棧檢查機制是分配在堆空間8個字節的x變量，但Valgrind的（由於某些原因）不能獲得意識到這一點，所以它標誌着它作爲無效寫入。也許這是valgrind 3.8.1中的一個限制，已經在3.10.0中解決了（考慮到在Debian的設置中，使用3.10.0，我沒有得到這個跟蹤）？
另外，我似乎在valgring FAQ是「和-fstack-check可以使堆棧跟蹤雪上加霜」但他們沒有提供關於原因，所以我不知道，如果問題是相關的信息太多了..
任何幫助或暗示，這有助於解釋這一點，高度讚賞。
編輯：作爲一項評論所說，我包括CentOS的6.x的情況下，dissasembled代碼，與-g3編譯和使用objdump --source test。我在這裏包括與main（）和f（）函數相對應的部分，但是可以找到完整的轉儲here。
二進制編譯-fstack-check：
0000000000400474 <f>:
int f(int i)
{
400474: 55 push %rbp
400475: 48 89 e5 mov %rsp,%rbp
400478: 89 7d fc mov %edi,-0x4(%rbp)
return i;
40047b: 8b 45 fc mov -0x4(%rbp),%eax
}
40047e: c9 leaveq
40047f: c3 retq
0000000000400480 <main>:
int main(int argC, char* argV[])
{
400480: 55 push %rbp
400481: 48 89 e5 mov %rsp,%rbp
400484: 48 83 ec 20 sub $0x20,%rsp
400488: 89 7d ec mov %edi,-0x14(%rbp)
40048b: 48 89 75 e0 mov %rsi,-0x20(%rbp)
int x = f(12);
return 0;
40048f: 48 8d 84 24 08 d0 ff lea -0x2ff8(%rsp),%rax
400496: ff
400497: 48 c7 00 00 00 00 00 movq $0x0,(%rax)
return i;
}
int main(int argC, char* argV[])
{
int x = f(12);
40049e: bf 0c 00 00 00 mov $0xc,%edi
4004a3: e8 cc ff ff ff callq 400474 <f>
4004a8: 89 45 fc mov %eax,-0x4(%rbp)
return 0;
4004ab: b8 00 00 00 00 mov $0x0,%eax
}
4004b0: c9 leaveq
4004b1: c3 retq
二進制編譯時沒有-fstack-check：
0000000000400474 <f>:
int f(int i)
{
400474: 55 push %rbp
400475: 48 89 e5 mov %rsp,%rbp
400478: 89 7d fc mov %edi,-0x4(%rbp)
return i;
40047b: 8b 45 fc mov -0x4(%rbp),%eax
}
40047e: c9 leaveq
40047f: c3 retq
0000000000400480 <main>:
int main(int argC, char* argV[])
{
400480: 55 push %rbp
400481: 48 89 e5 mov %rsp,%rbp
400484: 48 83 ec 20 sub $0x20,%rsp
400488: 89 7d ec mov %edi,-0x14(%rbp)
40048b: 48 89 75 e0 mov %rsi,-0x20(%rbp)
int x = f(12);
40048f: bf 0c 00 00 00 mov $0xc,%edi
400494: e8 db ff ff ff callq 400474 <f>
400499: 89 45 fc mov %eax,-0x4(%rbp)
return 0;
40049c: b8 00 00 00 00 mov $0x0,%eax
}
4004a1: c9 leaveq
4004a2: c3 retq
EDIT2：我已經在CentOS的當下（3.13.0）與最新的valgrind測試版6.8，我也遇到同樣的問題。
如果您更改main的返回值，即「1」以外的任何值，您是否檢查過該行爲？ – cse
我也嘗試過'return 0'和'return 2'，結果在CentOS 6.6中使用'-fstack-check'是相同的（即「無效寫入」）。無論如何感謝您的建議！ – fgalan
你可以粘貼拆散的代碼嗎？ – alinsoar