On 2021-08-25 07:46, John Paul Adrian Glaubitz wrote: > Hello! > > On 8/24/21 10:59 PM, Aurelien Jarno wrote: > > With the removal of the libc6-xen package in glibc 2.32, the only > > package still using the hwcap infrastructure is libc6.1-alphaev67. The > > hwcap infrastructure consists in upstream support for looking for > > libraries in the hwcap directories, plus Debian specific patches to > > support disabling hwcap with the /etc/ld.so.nohwcap, plus some mechanism > > in the maintainer scripts to disable hwcap support until all libc6 > > packages are configured. > > > > The various optimized packages have been replaced with time by other > > mechanisms such as indirect function support (IFUNC), or runtime atomic > > selection in GCC (-moutline-atomics). > > Isn't this type of architecture optimization support currently seeing a > revival due to many distributions looking into providing optimized x86_64 > variants? [1]
Yes, but that's unrelated. The plan is not to drop the hwcap mechanism from upstream code (which btw got extended in glibc 2.33). That will still be supported for instance for scientific libraries like in the link you provided. The goal is to stop providing optimized glibc through the hwcap mechanism (as the optimization is done using GCC or GNU IFUNC for many architectures), so that we can get rid of all the code enabling safe upgrade of the libc6 package. This part is Debian specific because we need to support online upgrades, so version version mismatch between base and hwcap libraries must not happen. If optimizations for the ev67 CPU is essential, an alternative is to ship both the base and hwcap versions in the same libc6.1 package. This causes an additional 4 MiB of possibly useless files to be installed on a system, something that has been considered too big for other architectures. Before going that way, we should check if the resulting optimization is worth the hassle, especially that we have to disable bit rotting assembly code from upstream (both baseline and alphaev67 optimized) to get the testsuite passing. Regards, Aurelien -- Aurelien Jarno GPG: 4096R/1DDD8C9B [email protected] http://www.aurel32.net
