On Sun, 07 Aug 2016 22:23:02 +0200 Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Friday, August 5, 2016 10:11:58 PM CEST Nicholas Piggin wrote: > > Hello, > > > > I have 3 different things in this patchset. All arch specific, but all > > involve kbuild changes, so I'd like to discuss them with kbuild > > maintainers. The goal has been to improve long standing linking > > difficulties with the powerpc kernel. > > > > * First, building kernel using thin archives rather than incremental > > linking. This seems quite clean and is per-arch, so I hope it should > > not be too controversial. > > > > * Second, building kernel using -ffunction-sections -fdata-sections, > > --gc-sections. Yes, I'm spinning the wheel again. It was motivated > > by tiny codesize regression in the first patch, but the results seem > > too good to ignore. > > > > * Third, allowing architecture to run a tool over module after it has > > been linked. Powerpc wants to use it in order to relocate "alternate > > code" instructions that get don't get linked at their runtime > > address. No idea if this is the right approach wrt kbuild, but it > > seems to work. > > > > I have included the powerpc code for the first two as a reference. The > > third is much bigger and mostly uninteresting for this cc list, but it > > can be found here: > > > > https://patchwork.ozlabs.org/patch/651006/ > > > > Comments appreciated. > > > > > > I've started tested this a bit on ARM now. The first things I noticed > are: > > 1. /home/arnd/cross-gcc/bin/arm-linux-gnueabi-ld: warning: drivers/xen/efi.o uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail > > (actually this one has been present since the first version that > stopped using recursive linking, I did 971a69db7dc0 ("Xen: don't > warn about 2-byte wchar_t in efi") when I first saw the bug, but > that fix no longer works and we have to do this differently > > 2. big-endian builds on ARM stopped working, I now get > > 22:53:02 CC init/do_mounts_md.o > 22:53:02 LD init/mounts.o > /home/arnd/cross-gcc/bin/arm-linux-gnueabi-ld: init/do_mounts.o: compiled for a big endian system and target is little endian > /home/arnd/cross-gcc/bin/arm-linux-gnueabi-ld: failed to merge target specific data of file init/do_mounts.o > > The problem seems to be that we don't pass the correct linker > flags any more, it should be using --be8 from > > arch/arm/Makefile:LDFLAGS_vmlinux += --be8 > arch/arm/Makefile:LDFLAGS_MODULE += --be8 > > but that somehow is lost. These both seem like linker flags are being lost for some reason, but I don't really know why. Maybe ARM's Makefile. I don't have an ARM build setup but I'll try to help track it down when I get some time. > 3. drivers/firmware/efi/libstub/lib.a: error adding symbols: Archive has no index; run ranlib to add one > > haven't investigated at all, turned off EFI for now. Okay this looks like a bug in patch 2 (caused by me, not Stephen!) For thin archives, cmd_link_l_target should be: cmd_link_l_target = rm -f $@; $(AR) rcT$(KBUILD_ARFLAGS) $@ $(lib-y) (note no "S" option). Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
