From imp@bsdimp.com Sat Jan 9 16:17:33 2016 Date: Sat, 9 Jan 2016 16:17:26 -0500 From: Warner Losh To: monthly@freebsd.org Subject: hardware ABI transition report armv6 hard float default ABI Warner Losh imp@freebsd.org Blog entry about this

Work on moving armv6 from a soft float ABI (using hardware floating point) to a fully hardware float API moves forward. The ability to have both soft and hard ABI libraries on the same system is working. All armv6 and armv7 systems we support have hardware floating point. We currently use the hardware float, but with a slightly un-optimal ABI for compatibility with older versions of FreeBSD. The ABI differences are only at the user level: The kernel doesn't care what floating point ABI is used, and both types of binaries can run at the same time.

The run time linker now knows if a binary uses the hardware float ABI or the software float ABI by looking at some fields in the ELF header. The linker uses different paths and config files for hard vs soft binaries. The rc system has been enhanced to load the software float paths. ldconfig now understands soft libraries in much the same way it understands 32-bit libraries on 64-bit systems. No additional kernel support was necessary for this, apart from a minor patch to pass the elf header information to the binary which has been in the tree since last summer.

The experimental armv6hf MACHINE_ARCH will be retired after a transition period. It will cease to mean anything different than armv6 after the build system changes go in. Support for building soft-float ABI libraries will remain in the tree to support the WITH_LIBSOFT option.

Complete documentation needs to be written. Hooks into the FreeBSD build system to generate soft float and to transition to hard float after a flag day need to be polished up and committed. And of course a number of different upgrade / coexistence scenarios need to be tested. A full package run needs to be done to assess the latest state of the ports tree. Work should be completed by the end of January.