On Thu, 22 Sep 2022 06:31:45 +0100, Denis Nikitin <denik@xxxxxxxxxxxx> wrote: > > Kernel build with clang and KCFLAGS=-fprofile-sample-use fails with: > > error: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o: Unexpected SHT_REL > section ".rel.llvm.call-graph-profile" > > Starting from 13.0.0 llvm can generate SHT_REL section, see > https://reviews.llvm.org/rGca3bdb57fa1ac98b711a735de048c12b5fdd8086. > gen-hyprel does not support SHT_REL relocation section. > > Remove ".llvm.call-graph-profile" SHT_REL relocation from kvm_nvhe > to fix the build. > > Signed-off-by: Denis Nikitin <denik@xxxxxxxxxxxx> > --- > V1 -> V2: Remove the relocation instead of disabling the profile-use flags. > --- > arch/arm64/kvm/hyp/nvhe/Makefile | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile > index b5c5119c7396..49ec950ac57b 100644 > --- a/arch/arm64/kvm/hyp/nvhe/Makefile > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile > @@ -78,8 +78,10 @@ $(obj)/kvm_nvhe.o: $(obj)/kvm_nvhe.rel.o FORCE > > # The HYPREL command calls `gen-hyprel` to generate an assembly file with > # a list of relocations targeting hyp code/data. > +# Starting from 13.0.0 llvm emits SHT_REL section '.llvm.call-graph-profile' > +# when profile optimization is applied. gen-hyprel does not support SHT_REL. > quiet_cmd_hyprel = HYPREL $@ > - cmd_hyprel = $(obj)/gen-hyprel $< > $@ > + cmd_hyprel = $(OBJCOPY) -R .llvm.call-graph-profile $<; $(obj)/gen-hyprel $< > $@ I was really hoping that you'd just drop the flags from the CFLAGS instead of removing the generated section. Something like: diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile index b5c5119c7396..e5b2d43925b4 100644 --- a/arch/arm64/kvm/hyp/nvhe/Makefile +++ b/arch/arm64/kvm/hyp/nvhe/Makefile @@ -88,7 +88,7 @@ quiet_cmd_hypcopy = HYPCOPY $@ # Remove ftrace, Shadow Call Stack, and CFI CFLAGS. # This is equivalent to the 'notrace', '__noscs', and '__nocfi' annotations. -KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI), $(KBUILD_CFLAGS)) +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI) -fprofile-sample-use, $(KBUILD_CFLAGS)) # KVM nVHE code is run at a different exception code with a different map, so # compiler instrumentation that inserts callbacks or checks into the code may However, I even failed to reproduce your problem using LLVM 14 as packaged by Debian (if that matters, I'm using an arm64 build machine). I build the kernel with: $ make LLVM=1 KCFLAGS=-fprofile-sample-use -j8 vmlinux and the offending object only contains the following sections: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o: file format elf64-littleaarch64 Sections: Idx Name Size VMA LMA File off Algn 0 .hyp.idmap.text 00000ae4 0000000000000000 0000000000000000 00000800 2**11 CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE 1 .hyp.text 0000e988 0000000000000000 0000000000000000 00001800 2**11 CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE 2 .hyp.data..ro_after_init 00000820 0000000000000000 0000000000000000 00010188 2**3 CONTENTS, ALLOC, LOAD, DATA 3 .hyp.rodata 00002e70 0000000000000000 0000000000000000 000109a8 2**3 CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA 4 .hyp.data..percpu 00001ee0 0000000000000000 0000000000000000 00013820 2**4 CONTENTS, ALLOC, LOAD, DATA 5 .hyp.bss 00001158 0000000000000000 0000000000000000 00015700 2**3 ALLOC 6 .comment 0000001f 0000000000000000 0000000000000000 00017830 2**0 CONTENTS, READONLY 7 .llvm_addrsig 000000b8 0000000000000000 0000000000000000 0001784f 2**0 CONTENTS, READONLY, EXCLUDE 8 .altinstructions 00001284 0000000000000000 0000000000000000 00015700 2**0 CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA 9 __jump_table 00000960 0000000000000000 0000000000000000 00016988 2**3 CONTENTS, ALLOC, LOAD, RELOC, DATA 10 __bug_table 0000051c 0000000000000000 0000000000000000 000172e8 2**2 CONTENTS, ALLOC, LOAD, RELOC, DATA 11 __kvm_ex_table 00000028 0000000000000000 0000000000000000 00017808 2**3 CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA 12 .note.GNU-stack 00000000 0000000000000000 0000000000000000 00027370 2**0 CONTENTS, READONLY So what am I missing to trigger this issue? Does it rely on something like PGO, which is not upstream yet? A bit of handholding would be much appreciated. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
