On Wed, Apr 10, 2024 at 10:37:42AM +0200, Ard Biesheuvel wrote: > On Wed, 10 Apr 2024 at 10:22, Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > > > On Tue, Apr 09, 2024 at 05:01:36PM +0200, Ard Biesheuvel wrote: > > > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > > > If the BTF code is enabled in the build configuration, the start/stop > > > BTF markers are guaranteed to exist in the final link but not during the > > > first linker pass. > > > > > > Avoid GOT based relocations to these markers in the final executable by > > > providing preliminary definitions that will be used by the first linker > > > pass, and superseded by the actual definitions in the subsequent ones. > > > > > > Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so > > > that inadvertent references to this section will trigger a link failure > > > if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF. > > > > > > Note that Clang will notice that taking the address of__start_BTF cannot > > > yield NULL any longer, so testing for that condition is no longer > > > needed. > > > > > > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > --- > > > include/asm-generic/vmlinux.lds.h | 9 +++++++++ > > > kernel/bpf/btf.c | 4 ++-- > > > kernel/bpf/sysfs_btf.c | 6 +++--- > > > 3 files changed, 14 insertions(+), 5 deletions(-) > > > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > > index e8449be62058..4cb3d88449e5 100644 > > > --- a/include/asm-generic/vmlinux.lds.h > > > +++ b/include/asm-generic/vmlinux.lds.h > > > @@ -456,6 +456,7 @@ > > > * independent code. > > > */ > > > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > > > + PRELIMINARY_BTF_DEFINITIONS \ > > > PROVIDE(kallsyms_addresses = .); \ > > > PROVIDE(kallsyms_offsets = .); \ > > > PROVIDE(kallsyms_names = .); \ > > > @@ -466,6 +467,14 @@ > > > PROVIDE(kallsyms_markers = .); \ > > > PROVIDE(kallsyms_seqs_of_names = .); > > > > > > +#ifdef CONFIG_DEBUG_INFO_BTF > > > +#define PRELIMINARY_BTF_DEFINITIONS \ > > > + PROVIDE(__start_BTF = .); \ > > > + PROVIDE(__stop_BTF = .); > > > +#else > > > +#define PRELIMINARY_BTF_DEFINITIONS > > > +#endif > > > > hi, > > I'm getting following compilation fail when CONFIG_DEBUG_INFO_BTF is disabled > > > > [jolsa@krava linux-qemu]$ make > > CALL scripts/checksyscalls.sh > > DESCEND objtool > > INSTALL libsubcmd_headers > > UPD include/generated/utsversion.h > > CC init/version-timestamp.o > > LD .tmp_vmlinux.kallsyms1 > > ld: kernel/bpf/btf.o: in function `btf_parse_vmlinux': > > /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5988: undefined reference to `__start_BTF' > > ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__stop_BTF' > > ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__start_BTF' > > make[2]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1 > > make[1]: *** [/home/jolsa/kernel/linux-qemu/Makefile:1160: vmlinux] Error 2 > > make: *** [Makefile:240: __sub-make] Error 2 > > > > maybe the assumption was that kernel/bpf/btf.o is compiled only > > for CONFIG_DEBUG_INFO_BTF, but it's actually: > > > > obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o > > > > Interesting. I did build test this with and without > CONFIG_DEBUG_INFO_BTF, but not with CONFIG_BPF_SYSCALL=y and > CONFIG_DEBUG_INFO_BTF=n. > > > I guess we just need !CONFIG_DEBUG_INFO_BTF version of btf_parse_vmlinux > > function > > > > The below gives me a working build. > > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -5971,6 +5971,9 @@ struct btf *btf_parse_vmlinux(void) > struct btf *btf = NULL; > int err; > > + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) > + return ERR_PTR(-ENOENT); nice, so this basically eliminates the rest of the function, I did not know this would work build's fine now, thanks jirka > + > env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN); > if (!env) > return ERR_PTR(-ENOMEM);
