How to use AddressSanitizer with GCC?

Make sure you have libasan installed. For example, in Fedora:

dnf install libasan libasan-static

You need to add the switch -lasan -fsanitize=address to your both your compile and link command line to link the correct library.

Note: the original answer -lasan is outdated and should not be used, as per comments

You need to add -fsanitize=address to compiler flags (both CFLAGS and CXXFLAGS) and linker flags (LDFLAGS). You've probably added it to your compiler flags only.

Note that using explicit -lasan option has been widely discouraged by ASan developers (e.g. here) as it misses some other important linker flags. The only recommended way to link is to use -fsanitize=address.

As a side note, for more aggressive verification flags check Asan FAQ (look for "more aggressive diagnostics").