What is the use of ".map" file in the g++ command?

Question

I'm building an RPM and while building I found following command is used to build one shared object of RPM.

g++ /*some compiler options*/ -O1 -Wl,--version-script abc.map -L<some paths> and the remaining command.

I did not understood the what is the use of "--version-script" option and "abc.map" file in the command. What it does? Follwoing is the content of "abc.map" file.

URE_1{
    global:
       _ZTI*; _ZTS*; # weak RTTI symbols for C++ exceptions
    /*some method names explicitly*/
    local:
     *;
}

I think its related to making availability of symbols in the "shared object" file but I'm not sure.

Read https://www.gnu.org/software/gnulib/manual/html_node/LD-Version-Scripts.html and https://sourceware.org/binutils/docs/ld/VERSION.html about _Linker Version Scripts_. Or see http://stackoverflow.com/questions/435352/limiting-visibility-of-symbols-when-linking-shared-libraries/452955 — FrankH., Mar 03 '14 at 16:29

score 1 · Accepted Answer · answered Mar 03 '14 at 07:13

1

I think its related to making availability of symbols in the "shared object" file but I'm not sure.

You are right.

See 3.9 VERSION Command:

The linker supports symbol versions when using ELF. Symbol versions are only useful when using shared libraries. The dynamic linker can use symbol versions to select a specific version of a function when it runs a program that may have been linked against an earlier version of the shared library.

answered Mar 03 '14 at 07:13

Lee Duhem

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Yes, an example of this is when Red Hat backports a patch, they will often tag it. Then newer versions of other software will explicitly note they need a certain flagged version. I ran into it with a patched `expat` 1.x. – Aaron D. Marasco Mar 03 '14 at 20:51

What is the use of ".map" file in the g++ command?

1 Answers1