Setting up glibc dev environment

These instructions a just a quick (and terse) run through on how you can setup and develop glibc should you need to.

Get & build libc

cvs -z 9 -d login
cvs -z 9 -d co libc

build libc, using separate object directory as required

mkdir glibc-obj
cd glibc-obj
../libc/configure --prefix=/usr --enable-add-ons=nptl --prefix=/usr

It is very important to set --prefix=/usr

Create a chroot

debootstrap sid ./the-chroot

You might like to setup the chroot (install gcc, fix up the /etc/apt/sources list, etc) and then make a tar of it, so that when you break it you can just delete it and untar the new one. You might also like to modify /etc/bash.bashrc to give you a different prompt so you know you are in the chroot.

TO install glibc, you need in addition to what debootstrap provides:

On the other hand, you can delete a whole heap of stuff;

Create a script

Create a script to

as an example

if [ ! -d ./the-chroot/usr/src/libc ] ; then
        sudo mkdir ./the-chroot/usr/src/libc

if [ ! -d ./the-chroot/usr/src/libc-obj ] ; then
        sudo mkdir ./the-chroot/usr/src/libc-obj

sudo mount --bind libc ./the-chroot/usr/src/libc
sudo mount --bind libc-obj ./the-chroot/usr/src/libc-obj

sudo chroot ./the-chroot

sudo umount ./the-chroot/usr/src/libc
sudo umount ./the-chroot/usr/src/libc-obj

Install new libc

Debian ships the NPTL libraries in /lib/tls (correctly), but for our development version we don't really care about having the correct libraries setup. Since make install won't put things in /lib/tls, if it exists the new version that we install will look at the hardware capabilites, decide to check for optimised libraries in the tls subdirectory and find them, only to completely fail when they are totally the wrong version.

The simplest way to avoid that is to set LD_ASSUME_KERNEL=2.4.0 to fool the dynamic loader into not looking for these files, then delete /lib/tls and install your new system (since we enabled tls with --enable-tls they'll be TLS libraries anyway).

Inside the chroot!

rm -rf /lib/tls
cd /usr/src/libc-obj
make install

once you have installed, you can unset the LD_ASSUME_KERNEL since the new libraries will be quite happy with everything in the default place. Of course this isn't as robust, and if you do go back to a kernel that can't support the latest libraries it won't work. But this is just for development, not production!


Now you can just make your changes outside your chroot, and thanks to the bind mount install them inside your chroot and do any testing you require.


If you specify

CFLAGS=-O2 -gdwarf-2 -g3

gcc will do some macro expansion and generally provide you with a nicer debugging experience (n.b. you need the O2 as libc won't build without optimisation on). The trade off is disk space used.

IA64wiki: GlibcDevelopmentEnvironment (last edited 2009-12-10 03:14:07 by localhost)

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