[uclibc-ng-devel] >uclibc-ng-1.0.18 on Gentoo

Hi everyone, I'm kinda silent on the list so people may not know that Gentoo supports uclibc-ng as a replacement for glibc. As a from source distro, we can do that. I also support Gentoo+musl. A few months back I switched from uclibc to uclibc-ng for obvious reasons. Its important for our users that we provide a forward migration path. The migration from uclibc -> uclibc-ng was a bit rocky but doable. [See https://wiki.gentoo.org/wiki/Project:Hardened_uClibc]. Since then, there have been two major changes to uclibc-ng which necessitated some more extra steps: 1) the coalescing of the breakout libraries like libdl.so, libm.so etc into libc.so. and 2) dropping obstack support. I'm going to outline the steps for forward migration here as an RFC. I'm also going to push out a news item to our users. Please comment 1. First we address the breakout libraries. Make sure you are on either uclibc-ng-1.0.18 or 1.0.19 and rebuild world with emerge -evq @world This should ensure that all executables bypass any symlinks from libm.so (and friends) to libc.so and link directly against libc.so. You can reassure yourself afterwards that a particular ${executable} does not link against any of the breakout libraries by using readelf -d ${executable} | grep "NEEDED.*lib\(crypt\|dl\|m\|pthread\|rt\|resolv\|ubacktrace\|util\).so" At this point it is safe to upgrade to 1.0.20. Make sure you do not set the symlink-compat USE flag. This is the default behavior, but you can be explicit about it: USE="-symlink-compat" emerge =sys-libs/uclibc-ng-1.0.20 2. Now we will have to rebuild @world again and make sure that the packages' build systems think that our libc does NOT provide obstack, even though it does. A direct upgrade to 1.0.21 will break your system because many critical executables will not be able to find obstack* symbols. There's a few steps that will do the trick here: a. Remove the obstack.h header: mv /usr/include/obstack.h ~ b. Force any gnulib build to think it has to provide its own obstack: cp /usr/include/gnu-versions.h ~ sed -i -e '/#define _GNU_OBSTACK/d' /usr/include/gnu-versions.h c. Tell stdio.h to not expose some obstack function prototypes. This is accomplished by defining __UCLIBC_HAS_OBSTACK__ 0 via the uClibc_config.h file: cp /usr/include/bits/uClibc_config.h ~ sed -i -e '/__UCLIBC_HAS_OBSTACK__/ s/1/0/' /usr/include/bits/uClibc_config.h 3. Now we are ready to rebuild @world, but we must skip rebuilding uclibc-ng itself since it will just undo the changes in step 2! emerge -—keep-going -evq --exclude sys-libs/uclibc-ng @world Some packages might fail. dev-libs/gmp will fail. It is a critical part of the toolchain, and we must deal with it. 4. To rebuild dev-libs/gmp, we need to override its build system's search for obstack_vprintf(). Use ac_cv_func_obstack_vprintf=no emerge -1 gmp 5. At this point you may want to check that no ${executable} is looking for an undefined symbol that looks like obstack*. If an executable does have such an undefined symbol, it will break upon upgrade. That's okay as long as it isn't critical to your system! readelf -sW ${executable} | grep "UND.*obstack" 6. Now we can upgrade uclibc-ng: emerge sys-libs/uclibc-ng-1.0.21 7. Finally, we rebuild world one more time to fix any non-critical executables that still need obstack: emerge —evq @world