Error running Valgrind on Gentoo Linux: the strlen problem

If you have ever tried to install Valgrind on Gentoo Linux you may have come across this error when you try to run the program:

==20032== Memcheck, a memory error detector
==20032== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==20032== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==20032== Command: ./1.x
==20032==

valgrind: Fatal error at startup: a function redirection
valgrind: which is mandatory for this platform-tool combination
valgrind: cannot be set up. Details of the redirection are:
valgrind:
valgrind: A must-be-redirected function
valgrind: whose name matches the pattern: strlen
valgrind: in an object with soname matching: ld-linux-x86-64.so.2
valgrind: was not found whilst processing
valgrind: symbols from the object with soname: ld-linux-x86-64.so.2
valgrind:
valgrind: Possible fixes: (1, short term): install glibc's debuginfo
valgrind: package on this machine. (2, longer term): ask the packagers
valgrind: for your Linux distribution to please in future ship a non-
valgrind: stripped ld.so (or whatever the dynamic linker .so is called)
valgrind: that exports the above-named function using the standard
valgrind: calling conventions for this platform. The package you need
valgrind: to install for fix (1) is called
valgrind:
valgrind: On Debian, Ubuntu: libc6-dbg
valgrind: On SuSE, openSuSE, Fedora, RHEL: glibc-debuginfo
valgrind:
valgrind: Cannot continue -- exiting now. Sorry.

As it turns out, this is a common error but the internet is awash with confusing information so I will try to help by explain what I did to get it working.

You don't need to reinstall Valgrind. It's fine. But what you do need to do is re-install glibc but with special options enabled. Open up the make.conf file in vi or your favourite editor:

vi /etc/make.conf

The things you need to add are shown in bold:

CFLAGS="-march=nocona -O2 -pipe -ggdb -fno-builtin-strlen"

FEATURES="preserve-libs nostrip splitdebug"

When you save these changes you can reinstall glibc:

sudo emerge glibc

Come back in about half an hour and then Valgrind should work. It took me forever to get it working so I hope I save you some time. If you have the chance I recommend using a different distro instead of Gentoo. Use something with a lot of user support like Ubuntu.