Question

When compiling C source code with either gcc or Clang, I always use the -g flag to generate debugging information for gdb.

gcc -g -o helloworld helloworld.c

I noticed that some people recommend -g3 instead. What is the difference between the -g and -g3 flags? Also is there a difference between -g and -ggdb?

Answer 1

From the docs:

-g

Produce debugging information in the operating system’s native format (stabs, COFF, XCOFF, or DWARF 2). GDB can work with this
debugging information. On most systems that use stabs format, -g
enables use of extra debugging information that only GDB can use; this
extra information makes debugging work better in GDB but probably
makes other debuggers crash or refuse to read the program. If you want
to control for certain whether to generate the extra information, use
-gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).

…

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-ggdb

Produce debugging information for use by GDB. This means to use the most expressive format available (DWARF 2, stabs, or the native
format if neither of those are supported), including GDB extensions if
at all possible.

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-gvmslevel

Request debugging information and also use level to specify how much information. The default level is 2. Level 0 produces no
debug information at all. Thus, -g0 negates -g.

….

Level 3 includes extra information, such as all the macro definitions
present in the program. Some debuggers support macro expansion when
you use -g3.