多程序除錯

實際上，gdb 沒有對多程序程式除錯提供直接支援。例如，使用gdb除錯某個程序，如果該程序fork了子程序，gdb會繼續除錯該程序，子程序會不受干擾地執行下去。如果你事先在子程序**裡設定了斷點，子程序會收到sigtrap訊號並終止。那麼該如何除錯子程序呢？其實我們可以利用gdb的特點或者其他一些輔助手段來達到目的。此外，gdb 也在較新核心上加入一些多程序除錯支援。

本文介紹的方法能讓你把斷點設在子程序中，單步檢視子程序的運**況。但問題，如果我想在一次除錯中同時在父子程序中設定斷點，單步執行該怎麼做呢？

1 #include
2 #include
3 #include
4 #include
5 #include
6 #include
7 #include
8 #include
9 #include
1011 main()
19     pid_t pid;
20if((pid=fork())<0)
24if(pid==0)
30         arr[0]='
a';arr[1]='
b';arr[2]='
c';arr[3]='
\0';
31if(shmdt(arr)==-1)
35     }
36else
43         printf("
%s\n
",arr);
44if(shmdt(arr)==-1)
48     }
49 }

方法一：attach pid

ubuntu預設情況下你在gdb中使用attach id是許可權不夠的，所以你需要：sudo chmod +s /usr/bin/gdb

在父子程序中加一句while(pause) sleep(1);，讓其暫停，然後後台執行程式，通過ps獲取子程序的pid。（如下所示，ps顯示的./fork有兩個，orisun是程序的有效使用者，第乙個數字是程序id，第二個數字是其父程序id）

執行gdb，attach 子程序id

orisun@zcypc:~$ ./fork &
[1] 13294
orisun@zcypc:~$ ps -ef|grep fork
10279010
09:00 ?        00:00:01 dbus-daemon --
system --fork --activation=upstart
orisun    154610
09:00 ?        00:00:03 //bin/dbus-daemon --
fork --print-pid 5 --print-address 7 --session
orisun   1258410
20:23 ?        00:00:12 gedit /home/orisun/fork.c
orisun   13294
13239
020:53 pts/0
00:00:00 ./fork
orisun   13295
13294
020:53 pts/0
00:00:00 ./fork
orisun   13297
13239
020:54 pts/0
00:00:00 grep --
color=auto fork
orisun@zcypc:~$ gdb
gnu gdb (ubuntu/linaro 7.2-1ubuntu11) 7.2
or later 
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 "
i686-linux-gnu
".for bug reporting instructions, please see:
.(gdb) attach 13295
attaching to process 13295
reading symbols from /home/orisun/fork...done.
reading symbols from /lib/i386-linux-gnu/libc.so.6...reading symbols from /usr/lib/debug/lib/i386-linux-gnu/libc-2.13.so...done.
done.
loaded symbols for /lib/i386-linux-gnu/libc.so.6
reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done.
loaded symbols for /lib/ld-linux.so.2
0x00bd8416 in __kernel_vsyscall ()
(gdb) backtrace
#0  0x00bd8416 in __kernel_vsyscall ()
#1  0x0049bfc0 in __nanosleep_nocancel ()
at ../sysdeps/unix/syscall-template.s:82
#2  0x0049bde2 in __sleep (seconds=)
at ../sysdeps/unix/sysv/linux/sleep.c:138
#3  0x08048595 in main () at fork.c:25
(gdb) up 3
#3  0x08048595 in main () at fork.c:25
25while(pause) sleep(1); 
(gdb) list
20if((pid=fork())<0)
24if(pid==0)
(gdb) break
31breakpoint 1 at 0x8048600: file fork.c, line 31.
(gdb) set pause=0
(gdb) continue
continuing.
breakpoint 1, main () at fork.c:31
31if(shmdt(arr)==-1){
(gdb) p arr
$1 = 0xb77fb000 "
abc"
(gdb)

方法二：follow-fork-mode

不需要專門加while(pause) sleep(1);這種**了。

follow-fork-mode的用法為：

set follow-fork-mode [parent|child]

* parent: fork之後繼續除錯父程序，子程序不受影響。

* child: fork之後除錯子程序，父程序不受影響。

因此如果需要除錯子程序，在啟動gdb後：

(gdb) set follow-fork-mode child

並在子程序**設定斷點。

此外還有detach-on-fork引數，指示gdb在fork之後是否斷開（detach）某個程序的除錯，或者都交由gdb控制：

set detach-on-fork [on|off]

* on: 斷開除錯follow-fork-mode指定的程序。

* off: gdb將控制父程序和子程序。follow-fork-mode指定的程序將被除錯，另乙個程序置於暫停（suspended）狀態。

orisun@zcypc:~$ gdb ./fork
gnu gdb (ubuntu/linaro 7.2-1ubuntu11) 7.2
or later 
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 "
i686-linux-gnu
".for bug reporting instructions, please see:
...reading symbols from /home/orisun/fork...done.
(gdb) set follow-fork-mode child
(gdb) set detach-on-fork off
(gdb) break
31breakpoint 1 at 0x80485e3: file fork.c, line 31.
(gdb) r
starting program: /home/orisun/fork 
[new process 13534]
[switching to process 13534]
breakpoint 1, main () at fork.c:31
31if(shmdt(arr)==-1){
(gdb) p arr
$1 = 0xb7ffd000 "
abc"
(gdb) c
continuing.
program exited normally.
(gdb)

多程序除錯

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gdb除錯多程序

gdb除錯多程序

多程序除錯

gdb多程序除錯

gdb除錯多程序

gdb除錯多程序

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