Get source code for libc for debugging in gdb - c

Question

I am currently debugging an api from shared library libc6 using gdb
getaddrinfo()
which is being called from python module:
socket.getaddrinfo()
I have managed to set a breakpoint at getaddrinfo.c and I wish to navigate the execution in single steps.
Source files:
ldd --version
tells that I have glibc 2.19, and I have downloaded the source from here
http://ftp.gnu.org/gnu/libc/
But during single step debugging using gdb, it doesnt look like the line numbers are matching.
Is there a cleaner way to download the source for libc6
PS: I am new to gdb debugging, please do point out any needed info.

Answer 1

Ubuntu 22.04 minimal runnable example
See also: https://askubuntu.com/questions/487222/how-to-install-debug-symbols-for-installed-packages/1434174#1434174
In the case of glibc, the debug symbols already appear to come preinstalled, otherwise we would need to get them with:
printf "deb http://ddebs.ubuntu.com %s main restricted universe multiverse\n" $(lsb_release -cs){,-updates,-security,-proposed} | \
sudo tee -a /etc/apt/sources.list.d/ddebs.list
sudo apt install ubuntu-dbgsym-keyring
sudo apt update
sudo apt install coreutils-dbgsym
sudo apt install libc6-dbg
and then get source with:
sudo cp /etc/apt/sources.list /etc/apt/sources.list~
sudo sed -Ei 's/^# deb-src /deb-src /'
/etc/apt/sources.list sudo apt-get update
apt source libc6
which produces directory: glibc-2.35.
We then make a C hello world to test with:
main.c
#include <stdio.h>
int main(void) {
puts("hello");
}
and compile and GDB into it with:
gcc -ggdb3 -O0 -std=c99 -Wall -Wextra -pedantic -o main.out main.c
gdb -ex 'set substitute-path . glibc-2.35' main.out
and then test it out as:
(gdb) start
Temporary breakpoint 1 at 0x1151: file main.c, line 4.
Starting program: /home/ciro/tmp/main.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Temporary breakpoint 1, main () at main.c:4
4 puts("hello");
(gdb) s
__GI__IO_puts (str=0x555555556004 "hello") at ./libio/ioputs.c:33
33 {
(gdb) l
28 #include <string.h>
29 #include <limits.h>
30
31 int
32 _IO_puts (const char *str)
33 {
34 int result = EOF;
35 size_t len = strlen (str);
36 _IO_acquire_lock (stdout);
37
"We're in".
Some other versions of Ubuntu had sources at an absolute location like:
/tmp/build138741687/
in which case you would instead want:
set substitute-path /tmp/build138741687/ glibc-2.35