On Tue, Apr 11, 2023 at 2:46 PM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote: > > Hi Nick > > On Sat, 8 Apr 2023 at 01:22, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > > > Hi Ricardo, > > Thanks for the patch! Please make sure to cc our mailing list > > <llvm@xxxxxxxxxxxxxxx> for llvm specific issues. > > scripts/get_maintainer.pl should recommend it, or you can find it from > > clangbuiltlinux.github.io. You can also ping me internally for > > toolchain related issues. > > > > Start of thread. > > https://lore.kernel.org/lkml/20230321-kexec_clang16-v5-0-5563bf7c4173@xxxxxxxxxxxx/ > > > > On Thu, Mar 30, 2023 at 9:00 AM Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > > > On Thu, Mar 30, 2023 at 11:31:27AM -0400, Steven Rostedt wrote: > > > > On Thu, 30 Mar 2023 17:18:26 +0200 > > > > Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > > > > > > On Thu, Mar 30, 2023 at 11:15:23AM -0400, Steven Rostedt wrote: > > > > > > > Make sure that the .text section is not divided in multiple overlapping > > > > > > > sections. This is not supported by kexec_file. > > > > Perhaps this is related to CrOS' use of AutoFDO creating .text.hot? > > If so, it's probably more straightforward to straight up disable PGO > > for kexec. See also: > > > > commit bde971a83bbf ("KVM: arm64: nvhe: Fix build with profile optimization") > > It was indeed due to the AutoFDO, adding > > KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%, > $(KBUILD_CFLAGS)) > > to arch/x86/purgatory/Makefile > > It is definitely simpler than adding a linker script, but I am not > sure if it is the correct way to fix this... Seems like splitting > .text in multiple sections is an implementation detail of the compiler > and the only way to force it is with a linker script... Or am I > missing something? I think with the use of `unlikely` GCC will put code in .text.cold, so it is possible to trigger this using simpler means, but... > > Shall I send a new version with the KBUILD_CFLAGS ? I still think the cflags approach is way simpler. If someone tries to use unlikely in purgatory: "don't do that." Same for PGO. > > Thanks! > > > > > > > > > > > > > And? > > > > > > > > > > What is the failure scenario? Why are you fixing it? Why do we care? > > > > > > > > > > This is way too laconic. > > > > > > > > > > > > > Yeah, I think the change log in patch 1 needs to be in this patch too, > > > > which gives better context. > > > > > > Just read it. > > > > > > Why did it work with clang version < 16? > > > > I'll bet if we bisect llvm, we can spot what might have changed, which > > may give us a clue on how to get the old behavior back; maybe without > > the need for a linker script. > > > > Ricardo, how did you verify that your fix was correct? Surely we can > > check using command line utilities without needing a full blown kexec > > setup? If you can share more info, I can bisect llvm quickly. If it > > requires profile data, you'll need to share it, since CrOS engineers > > still have not posted public documentation on AutoFDO as I have > > repeatedly asked for. > > The simplest test is to run: > > $readelf -S arch/x86/purgatory/purgatory.ro | grep "] \.text" > [ 3] .text PROGBITS 0000000000000000 000002a0 > > If there is only one .text section then that kernel will be load > properly via kexec_file(). Got it, profile data will be required to reproduce then. If you can share. -- Thanks, ~Nick Desaulniers _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
