What's the use of .map files the linker produces?

Question

What is the use of .map files VC++ linker produces when /MAP parameter or \"Generate map file\" project setting is used? When do I need them and how do I benefit from them?<

Answer 1

Linker maps can be very useful in large projects when you need to track dependencies between compilation units and libraries. Typically, a linker will report a symbol which caused problems, and more often than not, a simple search for this symbol name won't return any results (or will return tons of false positives for symbols like read).

Without a linker map, the only option you have is to analyze all available source files (after preprocessing pass if macros were used, which is typically the case) and hope that you find the relevant spot.

Linker maps usually have a section called "reference by file/symbol" which tells you which object file was required by another object file of your project, and which symbol exactly was referenced.

I was once working on a project which had to be ported on a system without locale support. The linker was reporting "undefined reference to _localeconv_r" errors, which would have been a pain to track down by searching through the sources. Luckily, a GCC linker map file generated with -Map=output.map revealed all problematic functions with a single search.