Where are GDB symbols coming from?

Question

When I load Fedora 28\'s /usr/bin/ls file into GDB, I can access to the symbol abformat_init, even if it is not present as a string nor in the symb

Answer 1

Is there a program that allows to extract them outside of GDB?

Yes, you can use nm to extract the symbol, but you should look for the symbol in a separate debug info file, because the binary itself is stripped.

You can use readelf or objdump to know separate debug info file name, see How to know the name and/or path of the debug symbol file which is linked to a binary executable?:

$ objdump -s -j .gnu_debuglink /usr/bin/ls

/usr/bin/ls:     file format elf64-x86-64

Contents of section .gnu_debuglink:
 0000 6c732d38 2e33302d 362e6663 32392e78  ls-8.30-6.fc29.x
 0010 38365f36 342e6465 62756700 5cddcc98  86_64.debug.\...

On Fedora 29 the separate debug info file name for /usr/bin/ls is ls-8.30-6.fc29.x86_64.debug.

Normally, on Fedora, separate debug info is installed to /usr/lib/debug/ directory so the full path to debug info file is /usr/lib/debug/usr/bin/ls-8.30-6.fc29.x86_64.debug.

Now you can look for the symbol with nm:

$ nm /usr/lib/debug/usr/bin/ls-8.30-6.fc29.x86_64.debug | grep abformat_init
0000000000006d70 t abformat_init

Note that separate debug info should be installed with debuginfo-install, this is what gdb is telling you.