爲什麼gdb -s選項不加載符號文件？

Question

我想創建一個核心轉儲並使用gdb進行分析。這是我爲創建核心轉儲而寫的代碼。

#include <iostream> 

void bar() 
{ 
    char *p = (char *) 123; 
    std::cout << "bar start\n"; 
    std::cout << *p << "\n"; 
    std::cout << "bar end\n"; 
} 

void foo() 
{ 
    std::cout << "foo start\n"; 
    bar(); 
    std::cout << "foo end\n"; 
} 

int main() 
{ 
    foo(); 
} 

這是我的Makefile。

all: 
     g++ -g foo.cc -o foo 
     objcopy --only-keep-debug foo foo.dbg 
     objcopy --strip-debug foo 

clean: 
     rm -rf core* foo 

運行make和./foo之後，這是我的目錄樣子。

# ls 
core.28091 foo foo.cc foo.dbg Makefile 

我能夠像這樣分析核心轉儲。我通過指定可執行文件和核心文件作爲命令行參數來啓動gdb。然後我用symbol-file foo.dbg命令加載foo.dbg中的符號。

[root@centos crash]# gdb foo core.28091 
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-60.el6_4.1) 
Copyright (C) 2010 Free Software Foundation, Inc. 
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> 
This is free software: you are free to change and redistribute it. 
There is NO WARRANTY, to the extent permitted by law. Type "show copying" 
and "show warranty" for details. 
This GDB was configured as "x86_64-redhat-linux-gnu". 
For bug reporting instructions, please see: 
<http://www.gnu.org/software/gdb/bugs/>... 
Reading symbols from /root/lab/crash/foo...(no debugging symbols found)...done. 
[New Thread 28091] 
Missing separate debuginfo for 
Try: yum --disablerepo='*' --enablerepo='*-debug*' install /usr/lib/debug/.build-id/81/a81be2e44c93640adedb62adc93a47f4a09dd1 
Reading symbols from /usr/lib64/libstdc++.so.6...(no debugging symbols found)...done. 
Loaded symbols for /usr/lib64/libstdc++.so.6 
Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done. 
Loaded symbols for /lib64/libm.so.6 
Reading symbols from /lib64/libgcc_s.so.1...(no debugging symbols found)...done. 
Loaded symbols for /lib64/libgcc_s.so.1 
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done. 
Loaded symbols for /lib64/libc.so.6 
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done. 
Loaded symbols for /lib64/ld-linux-x86-64.so.2 
Core was generated by `./foo'. 
Program terminated with signal 11, Segmentation fault. 
#0 0x000000000040076f in bar()() 
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.132.el6.x86_64 libgcc-4.4.7-4.el6.x86_64 libstdc++-4.4.7-4.el6.x86_64 
(gdb) symbol-file foo.dbg 
Reading symbols from /root/lab/crash/foo.dbg...done. 
(gdb) bt 
#0 0x000000000040076f in bar() at foo.cc:8 
#1 0x00000000004007b7 in foo() at foo.cc:15 
#2 0x00000000004007d1 in main() at foo.cc:21 
(gdb) list 
12  void foo() 
13  { 
14   std::cout << "foo start\n"; 
15   bar(); 
16   std::cout << "foo end\n"; 
17  } 
18 
19  int main() 
20  { 
21   foo(); 
(gdb) 

但是，我想在命令行參數中指定符號文件名。但它似乎並不奏效。請參閱下面的輸出。

[root@centos crash]# gdb -s foo.dbg foo core.28091 
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-60.el6_4.1) 
Copyright (C) 2010 Free Software Foundation, Inc. 
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> 
This is free software: you are free to change and redistribute it. 
There is NO WARRANTY, to the extent permitted by law. Type "show copying" 
and "show warranty" for details. 
This GDB was configured as "x86_64-redhat-linux-gnu". 
For bug reporting instructions, please see: 
<http://www.gnu.org/software/gdb/bugs/>... 
Reading symbols from /root/lab/crash/foo...(no debugging symbols found)...done. 
[New Thread 28091] 
Missing separate debuginfo for 
Try: yum --disablerepo='*' --enablerepo='*-debug*' install /usr/lib/debug/.build-id/81/a81be2e44c93640adedb62adc93a47f4a09dd1 
Reading symbols from /usr/lib64/libstdc++.so.6...(no debugging symbols found)...done. 
Loaded symbols for /usr/lib64/libstdc++.so.6 
Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done. 
Loaded symbols for /lib64/libm.so.6 
Reading symbols from /lib64/libgcc_s.so.1...(no debugging symbols found)...done. 
Loaded symbols for /lib64/libgcc_s.so.1 
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done. 
Loaded symbols for /lib64/libc.so.6 
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done. 
Loaded symbols for /lib64/ld-linux-x86-64.so.2 
Core was generated by `./foo'. 
Program terminated with signal 11, Segmentation fault. 
#0 0x000000000040076f in bar()() 
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.132.el6.x86_64 libgcc-4.4.7-4.el6.x86_64 libstdc++-4.4.7-4.el6.x86_64 
(gdb) bt 
#0 0x000000000040076f in bar()() 
#1 0x00000000004007b7 in foo()() 
#2 0x00000000004007d1 in main() 
(gdb) list 
No symbol table is loaded. Use the "file" command. 

爲什麼它說，即使我已指定它作爲參數傳遞給-s選項沒有符號表已經被加載？

Answer 1

它看起來像gdb中的錯誤。 gdb將symarg設置爲-s後面的參數，但隨後在代碼中，它無條件地將symarg設置爲可執行文件的名稱。建議最小差異如下：

$ diff -C 1 main.c.orig main.c 
*** main.c.orig 2014-07-29 08:37:42.000000000 -0400 
--- main.c  2014-09-02 16:27:54.079039046 -0400 
*************** 
*** 864,866 **** 
     } 
!  symarg = argv[optind]; 
     execarg = argv[optind]; 
--- 864,866 ---- 
     } 
!  if (symarg == NULL) symarg = argv[optind]; 
     execarg = argv[optind]; 
*************** 
*** 877,879 **** 
     { 
!   symarg = argv[optind]; 
      execarg = argv[optind]; 
--- 877,879 ---- 
     { 
!   if (symarg == NULL) symarg = argv[optind]; 
      execarg = argv[optind];