一、gdb常用命令
二、GDB与多进程
#include<stdio.h> #include<sys/types.h> #include<stdlib.h> int main() { pid_t id = fork(); if(id < 0 ) { perror("fork"); exit(-1); }else if(id == 0) { printf("child id is %d, my father id is %d\n", getpid(), getppid()); }else { sleep(1); printf("father id id %d\n", getpid()); wait(NULL); } return 0; }
默认设置下，在调试多进程程序时GDB只会调用主进程，但是GDB（>V7.0）支持多进程的分别与同步调试。即GDB支持同时调试多个进程。只需要设置follow-fork-mode(默认为 parent)和detach-on-fork(默认为：on)即可。
follow-fork-mode detach-on-fork 说明
parent on 只调试主进程（GDB默认）
child on 只调试子进程
parent off 同时调试两个进程，gdb跟主进程，子进程block(阻塞)在fork位置child off 同时调试两个进程，gdb跟子进程，主进程block在fork位置
设置方法： set follow-fork-mode[parent|child] set detach-on-fork[on|off]
显示：show follow-fork-mode show detach-on-fork
查询正在调试的进程：info inferiors
显示GDB调试的所有inferior，GDB为他们分配ID。其中带*的进程是正在调试的进程。
（GDB将每一个被调试程序的执行状态记录在一个名为inferior的结构中。一般情况下一个inferior对应一个进程，每一个inferior都有自己的地址空间。inferior有时候会在进程没有启动时就存在）
切换调试的进程：inferior <inferior number>
通过该指令可以切换到ID为number的inferior进行调试。
调加新的调试进程：add-inferior[-copies n][-exec executable]
可以用file+executable来分配给inferior可执行文件。+增加n个inferior并执行程序为executable。如果不指定n只增加一个inferior。如果不指定executable，则执行程序留空，增加后可使用file命令重新指定执行程序。这时候创建的inferior其关联的进程并没启动。删除一个infnum 的inferior：remove-inferior infnum (如果inferior正在运行，则不能删除，删除之间需先kill或detach掉该inferior)
detach掉infnum的inferior：detach inferior infnum注意(inferior仍然存在，可以用run等命令执行)
kill 掉infnum的inferior：kill inferior infnum 注意(inferior仍然存在，可以用run等命令执行)
cfc:/app/tmp>gcc some.c -o some -g cfc:/app/tmp>gdb some GNU gdb (GDB) Red Hat Enterprise Linux (7.2-90.el6) 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 /app/tmp/some...done. (gdb) set follow-fork-mode Requires an argument. Valid arguments are child, parent. (gdb) set follow-fork-mode child (gdb) set detach-on-fork off (gdb) show follow-fork-mode Debugger response to a program call of fork or vfork is "child". (gdb) show detach-on-fork Whether gdb will detach the child of a fork is off. (gdb) info inferiors Num Description Executable * 1 <null> /app/tmp/some (gdb) break some.c:14 Breakpoint 1 at 0x4006e5: file some.c, line 14. (gdb) add-inferiors -copies 3 -exec /app/tmp/some Undefined command: "add-inferiors". Try "help". (gdb) add-inferior -copies 3 -exec /app/tmp/some Added inferior 2 Reading symbols from /app/tmp/some...done. Added inferior 3 Reading symbols from /app/tmp/some...done. Added inferior 4 Reading symbols from /app/tmp/some...done. (gdb) info inferiors Num Description Executable 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 <null> /app/tmp/some * 1 <null> /app/tmp/some (gdb) run Starting program: /app/tmp/some [New process 16964] Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 [Switching to process 16964] Breakpoint 1, main () at some.c:14 14 printf("child id is %d, my father id is %d\n", getpid(), getppid()); Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 (gdb) n child id is 16964, my father id is 16961 21 return 0; (gdb) info inferiors Num Description Executable * 5 process 16964 /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 <null> /app/tmp/some 1 process 16961 /app/tmp/some (gdb) remove inferiors 5 No symbol "inferiors" in current context. (gdb) remove-inferiors 5 Undefined command: "remove-inferiors". Try "help". (gdb) remove-inferiors infnum Undefined command: "remove-inferiors". Try "help". (gdb) detach inferior 5 Detaching from program: /app/tmp/some, process 16964 (gdb) info inferiors Num Description Executable * 5 <null> /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 <null> /app/tmp/some 1 process 16961 /app/tmp/some (gdb) kill inferior 5 Inferior has no threads. (gdb) inferior 2 [Switching to inferior 2 [process 0] (/app/tmp/some)] (gdb) info b Num Type Disp Enb Address What 1 breakpoint keep y <MULTIPLE> breakpoint already hit 1 time 1.1 y 0x00000000004006e5 in main at some.c:14 inf 5 1.2 y 0x00000000004006e5 in main at some.c:14 inf 4 1.3 y 0x00000000004006e5 in main at some.c:14 inf 3 1.4 y 0x00000000004006e5 in main at some.c:14 inf 2 1.5 y 0x00000000004006e5 in main at some.c:14 inf 1 (gdb) info inferiors Num Description Executable 5 <null> /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some * 2 <null> /app/tmp/some 1 process 16961 /app/tmp/some (gdb) run Starting program: /app/tmp/some [New process 17010] [Switching to process 17010] Breakpoint 1, main () at some.c:14 14 printf("child id is %d, my father id is %d\n", getpid(), getppid()); Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 (gdb) info inferiors Num Description Executable * 6 process 17010 /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) kill inferior 6 (gdb) info inferiors Num Description Executable * 6 <null> /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) run Starting program: /app/tmp/some [New process 17012] [Switching to process 17012] Breakpoint 1, main () at some.c:14 14 printf("child id is %d, my father id is %d\n", getpid(), getppid()); Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 (gdb) info inferiors Num Description Executable * 7 process 17012 /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) run The program being debugged has been started already. Start it from the beginning? (y or n) n Program not restarted. (gdb) n child id is 17012, my father id is 17011 21 return 0; (gdb) n 22 } (gdb) n 0x0000003d8a21ed1d in __libc_start_main () from /lib64/libc.so.6 (gdb) n Single stepping until exit from function __libc_start_main, which has no line number information. Program exited normally. (gdb) The program is not being run. (gdb) The program is not being run. (gdb) info inferiors Num Description Executable * 7 <null> /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) inferior 2 [Switching to inferior 2 [process 17009] (/app/tmp/some)] [Switching to thread 3 (process 17009)] #0 0x0000003d8a2accbd in fork () from /lib64/libc.so.6 (gdb) inferior 3 [Switching to inferior 3 [process 0] (/app/tmp/some)] (gdb) info inferiors Num Description Executable 7 <null> /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some * 3 <null> /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) run Starting program: /app/tmp/some [New process 17036] [Switching to process 17036] Breakpoint 1, main () at some.c:14 14 printf("child id is %d, my father id is %d\n", getpid(), getppid()); Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 (gdb) info inferiors Num Description Executable * 8 process 17036 /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 process 17035 /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) s child id is 17036, my father id is 17035 21 return 0; (gdb) s 22 } (gdb) s 0x0000003d8a21ed1d in __libc_start_main () from /lib64/libc.so.6 (gdb) s Single stepping until exit from function __libc_start_main, which has no line number information. Program exited normally. (gdb) info inferiors Num Description Executable * 8 <null> /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 process 17035 /app/tmp/some 2 process 17009 /app/tmp/some 1 process 16961 /app/tmp/some (gdb) kill inferior 2 (gdb) info inferiors Num Description Executable 8 <null> /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 process 17035 /app/tmp/some * 2 <null> /app/tmp/some 1 process 16961 /app/tmp/some (gdb) kill inferior 3 (gdb) kill inferior 1 (gdb) info inferiors Num Description Executable 8 <null> /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some 2 <null> /app/tmp/some * 1 <null> /app/tmp/some (gdb) remove-inferior 2 (gdb) info inferiors Num Description Executable 8 <null> /app/tmp/some 6 process 17011 /app/tmp/some 4 <null> /app/tmp/some 3 <null> /app/tmp/some * 1 <null> /app/tmp/some (gdb)
