Ubuntu provides debug symbol as dbgsym package. This article will describe installing dbgsym and debugging package. This article will debug bash with debug symbol.
Table of Contents
1 Add repository of dbgsym
dbgsym package is published in ddebs.ubuntu.com. Add ddebs.ubuntu.com to repository list.
$ D=`lsb_release -cs`
$ sudo su -c "
cat <<EOF > /etc/apt/sources.list.d/ddebs.list
deb http://ddebs.ubuntu.com ${D} main restricted universe multiverse
deb http://ddebs.ubuntu.com ${D}-security main restricted universe multiverse
deb http://ddebs.ubuntu.com ${D}-updates main restricted universe multiverse
#deb http://ddebs.ubuntu.com ${D}-proposed main restricted universe multiverse
EOF
"
Import GPG key of ddebs.ubuntu.com.
$ wget -O - http://ddebs.ubuntu.com/dbgsym-release-key.asc | sudo apt-key add -
Update repository database.
$ sudo apt update -y
2 Install dbgsym package
The package which has a suffix of dbgsym provides debug symbol.
<package>-dbgsym
In case of bash is as below.
$ sudo apt install -y bash-dbgsym $ dpkg -L bash-dbgsym /. /usr /usr/lib /usr/lib/debug /usr/lib/debug/usr /usr/lib/debug/usr/bin /usr/lib/debug/usr/bin/clear_console /usr/lib/debug/bin /usr/lib/debug/bin/bash
GDB will search /usr/lib/debug automatically even if you do not specify path of debug symbol.
3 Download package source code
Ubuntu 16.04 disables deb-src by default. You need to enable deb-src for downloading package source code.
$ sudo su -c "grep '^deb ' /etc/apt/sources.list | \ sed 's/^deb/deb-src/g' > /etc/apt/sources.list.d/src.list"
Update repository database.
$ sudo apt update -y
Download package source code.
$ mkdir <package> $ cd <package> $ apt source <package>
In case of bash is as below.
$ mkdir ~/bash $ cd ~/bash $ apt source bash $ ls bash-4.3 bash_4.3-14ubuntu1.1.dsc bash_4.3-14ubuntu1.1.debian.tar.xz bash_4.3.orig.tar.gz
4 Install GDB
Install gdb64 for 64bit system or gdb for 32bit system.
$ sudo apt install -y gdb64
5 Debug package
Run GDB with command and path of source code.
$ gdb64 <command> --directory /path/to/source <snip> (gdb)
In case of bash is as below.
$ gdb64 bash --directory ~/bash/bash-4.3/
<snip>
(gdb) b main
Breakpoint 1 at 0x41eed0: file .././shell.c, line 361.
(gdb) r
Starting program: /bin/bash
warning: the debug information found in "/lib64/ld-2.23.so" does not
match "/lib64/ld-linux-x86-64.so.2" (CRC mismatch).
Breakpoint 1, main (argc=1, argv=0x7fffffffe1d8, env=0x7fffffffe1e8) at .././shell.c:361
warning: Source file is more recent than executable.
361 {
(gdb) l
356 int
357 main (argc, argv, env)
358 int argc;
359 char **argv, **env;
360 #endif /* !NO_MAIN_ENV_ARG */
361 {
362 register int i;
363 int code, old_errexit_flag;
364 #if defined (RESTRICTED_SHELL)
365 int saverst;
GDB command "la src" is useful for tracing source code.
(gdb) la src
