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

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?

A nice article on how to use map files for finding crashes.

http://www.codeproject.com/KB/debug/mapfile.aspx

Manually doing all this is very uninteresting.

I am not aware of any tools which can read map file and help in finding the crash location. If anybody knows please update us.

For embedded systems, map files are a lot more useful. (Although you wouldn't be using Visual C++ for that ;)

Things like knowing how close you are to running out of program/data memory, and what location a particular variable resides in, are important.

WinDBG uses .map and .pdb files to help debug crashes, when analysing .hdmp and .mdmp crash dumps.

Basically they map memory address offsets to functions and variables within the .exe (and/or loaded .dlls). Very useful in general if you need to figure out why a customer is upset. Even more useful when they prove it was not your fault.

The most useful way to debug "post-mortem" crashes is using WinDbg (Windows platform). Open it up, and open the crash dump. Then set the source path to point at the code (if you have it), the symbol path to point at your .map and .pdb and the image path to the .exe, and type "!analyse -v" in the command line. Now you have a full stack trace with lines of code and everything. Of course you need to have the correct version of the source code for the version of the exe's and DLLs you are debugging.

It's even better if you have the MS symbol server in the path, and if the full page heap was turned on or adplus was running. With ADPlus in particular you will likely have variable values captured as well.

Some favourite WinDbg resources of mine:
First stop :: http://www.microsoft.com/whdc/devtools/debugging/debugstart.mspx
Force load the symbols :: http://www.osronline.com/ShowThread.cfm?link=182377
Useful site :: http://www.dumpanalysis.org/blog/index.php/category/windbg-tips-and-tricks/page/7/

You need them rarely, but they can be handy debugging some problems because they give information on the location of functions and data.

For example:

• detailed information on all segments (code, data and other).
• link line numbers to code

You can use map files for debugging tools.

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.