How do I tell gcc (or ld) to link against debug versions of the standard c and c++ libraries

Question

I have debug versions of libstdc++ and libc, among others, and would like to link against them. They live in /usr/lib/debug as opposed to /usr/lib. Any ideas?

Answer 1

I believe the accepted answer is misleading in that the libraries in /usr/lib/debug is not a debug compiled (-g -O0 ...) version of libraries in /lib,/usr/lib but simply debug symbols stripped from the corresponding library in /lib,/usr/lib. See the explanation the accepted answers to How to use debug version of libc and for How to link against debug versions of libc and libstdc++ in GCC? more details.

Quotes:

The libraries in /usr/lib/debug are not real libraries. Rather, the contain only debug info, but do not contain .text nor .data sections of the real libc.so.6

and

On many Linux installations the debug libraries do not contain real code; they only contain the debug info. The two are separated so that you can choose not to install them if you don't need them and you are short of disk space, but the debug libraries are no good on their own.

Check yourself with:

objdump -h /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.19.so | grep -C1 text
 11 .text         001488a3  000000000001f520  000000000001f520  000002b4  2**4
                  ALLOC, READONLY, CODE

The .text segment is ALLOC but without CONTENTS. Compare with the corresponding library in /lib/x86_64-linux-gnu/libc-2.19.so:

$ objdump -h /lib/x86_64-linux-gnu/libc-2.19.so | grep -C1 text
 11 .text         001488a3  000000000001f520  000000000001f520  0001f520  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE

Answer 2

Assuming Linux,

1. Static libraries: add a -L/usr/lib/debug to your linker command line. gcc/ld will look there before default system directories. Use ldd command to verify that correct library versions were linked against (shared libraries only).
2. Shared libraries: set LD_LIBRARY_PATH=usr/lib/debug, and your application will pick up libraries from there even without step 1, as long as there is a version of a library, which is very likely if you are installing with distribution's package manager.

It's a good idea to do both, though, as some libraries may be only in static form.

Answer 3

Use linker flags. ld/gcc -L<LIBRARY_PATH> is important for link time only, regardless shared or static, you cannot link against library, if linker can't find it.

For shared libraries environment variable LD_LIBRARY_PATH is important for start up time. Dynamic libraries loader ld.so and ld-linux.so will look up there when you start your application.