Hi Ricardo, Thanks for your kind reply. On Fri, Sep 8, 2023 at 2:18 PM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote: > > Hi Song > > On Fri, 8 Sept 2023 at 01:08, Song Liu <song@xxxxxxxxxx> wrote: > > > > Hi Ricardo and folks, > > > > On Fri, May 19, 2023 at 7:48 AM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote: > > > > > > When upreving llvm I realised that kexec stopped working on my test > > > platform. > > > > > > The reason seems to be that due to PGO there are multiple .text sections > > > on the purgatory, and kexec does not supports that. > > > > > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> > > > > We are seeing WARNINGs like the following while kexec'ing a PGO and > > LTO enabled kernel: > > > > WARNING: CPU: 26 PID: 110894 at kernel/kexec_file.c:919 > > kexec_load_purgatory+0x37f/0x390 > > > > AFAICT, the warning was added by this set, and it was triggered when > > we have many .text sections > > in purgatory.ro. The kexec was actually successful. So I wonder > > whether we really need the > > WARNING here. If we disable LTO (PGO is still enabled), we don't see > > the WARNING any more. > > > > I also tested an older kernel (5.19 based), where we also see many > > .text sections with LTO. It > > kexec()'ed fine. (It doesn't have the WARN_ON() in > > kexec_purgatory_setup_sechdrs). > > You have been "lucky" that the code has chosen the correct start > address, you need to modify the linker script of your kernel to > disable PGO. > You need to backport a patch like this: > https://lore.kernel.org/lkml/CAPhsuW5_qAvV0N3o+hOiAnb1=buJ1pLzqYW9D+Bwft6hxJvAeQ@xxxxxxxxxxxxxx/T/#md68b7f832216b0c56bbec0c9b07332e180b9ba2b We already have this commit in our branch. AFAICT, the issue was triggered by LTO. So something like the following seems fixes it (I haven't finished the end-to-end test yet). Does this change make sense to you? Thanks again, Song diff --git i/arch/x86/purgatory/Makefile w/arch/x86/purgatory/Makefile index 8f71aaa04cc2..dc306fa7197d 100644 --- i/arch/x86/purgatory/Makefile +++ w/arch/x86/purgatory/Makefile @@ -19,6 +19,10 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS # optimization flags. KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%,$(KBUILD_CFLAGS)) +# When LTO is enabled, llvm emits many text sections, which is not supported +# by kexec. Remove -flto=* flags. +KBUILD_CFLAGS := $(filter-out -flto=%,$(KBUILD_CFLAGS)) + # When linking purgatory.ro with -r unresolved symbols are not checked, # also link a purgatory.chk binary without -r to check for unresolved symbols. PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib
