Commit 46fb0b62 authored by Alan Maguire's avatar Alan Maguire Committed by Andrii Nakryiko
Browse files

kbuild,bpf: Add module-specific pahole flags for distilled base BTF 



Support creation of module BTF along with distilled base BTF;
the latter is stored in a .BTF.base ELF section and supplements
split BTF references to base BTF with information about base types,
allowing for later relocation of split BTF with a (possibly
changed) base.  resolve_btfids detects the presence of a .BTF.base
section and will use it instead of the base BTF it is passed in
BTF id resolution.

Modules will be built with a distilled .BTF.base section for external
module build, i.e.

make -C. -M=path2/module

...while in-tree module build as part of a normal kernel build will
not generate distilled base BTF; this is because in-tree modules
change with the kernel and do not require BTF relocation for the
running vmlinux.

Signed-off-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Reviewed-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20240620091733.1967885-6-alan.maguire@oracle.com
parent 8646db23

scripts/Makefile.btf

+5 −0
Original line number Diff line number Diff line
@@ -21,8 +21,13 @@ else 
# Switch to using --btf_features for v1.26 and later.

pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs



ifneq ($(KBUILD_EXTMOD),)

module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base

endif



endif



pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust



export PAHOLE_FLAGS := $(pahole-flags-y)

export MODULE_PAHOLE_FLAGS := $(module-pahole-flags-y)

scripts/Makefile.modfinal

+1 −1
Original line number Diff line number Diff line
@@ -41,7 +41,7 @@ quiet_cmd_btf_ko = BTF [M] $@ 
	if [ ! -f vmlinux ]; then					\

		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \

	else								\

		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \

		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) $(MODULE_PAHOLE_FLAGS) --btf_base vmlinux $@; \

		$(RESOLVE_BTFIDS) -b vmlinux $@; 			\

	fi;