gdb로 postgresql backend process 디버깅하기

C function 을 작성할 때 gdb로 간단히 디버깅 할 수 있는 방법입니다. (참고로 gdb 명령에 익숙하지 않으시다면 optimizer.snu.ac.kr/yanne/ToolManuals/gdb.doc)

1. 먼저 컴파일 전 configure 를 이용하여 디버깅 레벨을 변경합니다.

("vaule optimized away" 메세지가 출력되면서 해당되는 변수값을 확인할 수 없는 경우가 많았습니다.)

./configure --enable-cassert --enable-debug CFLAGS="-ggdb -O0"

2. 새로운 backend process 를 생성하고 pid 를 확인합니다.

test=# select pg_backend_pid();
 pg_backend_pid 
----------------
           3167
(1 row)

3. gdb 를 pid 로 attach 하여 디버깅 실행

$ gdb -p 3193
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 
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:
.
Attaching to process 3193
Reading symbols from /usr/local/pgsql93/bin/postgres...done.
Reading symbols from /usr/lib64/libssl.so.10...(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/libssl.so.10
Reading symbols from /usr/lib64/libcrypto.so.10...(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/libcrypto.so.10
Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libm.so.6
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/libgssapi_krb5.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libgssapi_krb5.so.2
Reading symbols from /lib64/libkrb5.so.3...(no debugging symbols found)...done.
Loaded symbols for /lib64/libkrb5.so.3
Reading symbols from /lib64/libcom_err.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libcom_err.so.2
Reading symbols from /lib64/libk5crypto.so.3...(no debugging symbols found)...done.
Loaded symbols for /lib64/libk5crypto.so.3
Reading symbols from /lib64/libz.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libz.so.1
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
Reading symbols from /lib64/libkrb5support.so.0...(no debugging symbols found)...done.
Loaded symbols for /lib64/libkrb5support.so.0
Reading symbols from /lib64/libkeyutils.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libkeyutils.so.1
Reading symbols from /lib64/libresolv.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libresolv.so.2
Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.
[Thread debugging using libthread_db enabled]
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /lib64/libselinux.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libselinux.so.1
Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnss_files.so.2
0x0000003f002e98c2 in recv () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.132.el6_5.2.x86_64 keyutils-libs-1.4-4.el6.x86_64 krb5-libs-1.10.3-15.el6_5.1.x86_64 libcom_err-1.41.12-18.el6.x86_64 libselinux-2.0.94-5.3.el6_4.1.x86_64 openssl-1.0.1e-16.el6_5.14.x86_64 zlib-1.2.3-29.el6.x86_64
(gdb)

4. break-point를 생성

(gdb) b [디버깅 대상 함수명]
Breakpoint 1 at 0x57a733: file parser.c, line 42.
(gdb) 

5. 함수를 호출하여 디버깅 시작

test=# select [디버깅대상함수]; -- gdb 에서 프로그램을 실행할때까지 대기합니다.