On Wed, Aug 23, 2023 at 6:34 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > On Thu, Aug 24, 2023 at 8:30 AM Denis Nikitin <denik@xxxxxxxxxxxx> wrote: > > > > On Wed, Aug 23, 2023 at 4:02 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > > > On Wed, Aug 23, 2023 at 3:00 AM Fangrui Song <maskray@xxxxxxxxxx> wrote: > > > > > > > > On Tue, Aug 22, 2023 at 10:49 AM Denis Nikitin <denik@xxxxxxxxxxxx> wrote: > > > > > > > > > > .llvm.call-graph-profile section is added by clang when the kernel is > > > > > built with profiles (e.g. -fprofile-sample-use= or -fprofile-use=). > > > > > > > > > > The section contains edge information derived from text sections, > > > > > so .llvm.call-graph-profile itself doesn't need more analysis as > > > > > the text sections have been analyzed. > > > > > > > > > > This change fixes the kernel build with clang and a sample profile > > > > > which currently fails with: > > > > > > > > > > "FATAL: modpost: Please add code to calculate addend for this architecture" > > > > > > > > > Curious. > > > > > > This message is only displayed for REL. > > > > > > (Please not it is located in section_rel() function) > > > > > > > > > I think modern architectures use RELA instead of REL. > > > Which architecture are we talking about? > > > > Aarch64. There was also a report on x86-64 but the error message could be > > different there. > > > > > > > > > > > What does the output of this command look like? > > > > > > $ llvm-readelf -S vmlinux.o | grep .llvm.call-graph-profile > > > > > > > > > Is it REL? > > > > > > > [119] .llvm.call-graph-profile LLVM_CALL_GRAPH_PROFILE 0000000000000000 > > 1c74a458 0104c8 08 E 0 0 1 > > [120] .rel.llvm.call-graph-profile REL 0000000000000000 1c75a920 041320 10 > > I 26090 119 8 > > > Fangrui, > > Aarch64 uses RELA for other sections, but REL for this one. > > I'd like to confirm if this is an expectation, not a toolchain bug. Hi Masahiro, Yes, using REL is intentional. It makes the relocations of .llvm.call-graph-profile smaller. The format encodes the (from,to,count) information with * the section content holds 'count' * two R_*_NONE relocations hold 'from' and 'to'. The addend field is unused, therefore REL is better. -- 宋方睿
