[PATCH] BTF_OBJCOPY

[Ihor Solodrai]

---
 Makefile                             |  6 +++++-
 lib/Kconfig.debug                    |  1 +
 scripts/gen-btf.sh                   | 10 +++++-----
 scripts/link-vmlinux.sh              |  2 +-
 tools/testing/selftests/bpf/Makefile |  4 ++--
 5 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index 18adf5502244..b7797a85b8c2 100644
--- a/Makefile
+++ b/Makefile
@@ -534,6 +534,9 @@ CLIPPY_DRIVER	= clippy-driver
 BINDGEN		= bindgen
 PAHOLE		= pahole
 RESOLVE_BTFIDS	= $(objtree)/tools/bpf/resolve_btfids/resolve_btfids
+# Always use GNU objcopy when manipulating BTF sections to work around
+# a bug in llvm-objcopy: https://github.com/llvm/llvm-project/issues/168060
+BTF_OBJCOPY	= $(CROSS_COMPILE)objcopy
 LEX		= flex
 YACC		= bison
 AWK		= awk
@@ -627,7 +630,8 @@ export CLIPPY_CONF_DIR := $(srctree)
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC HOSTPKG_CONFIG
 export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN
 export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
-export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
+export CPP AR NM STRIP OBJCOPY OBJDUMP READELF LEX YACC AWK INSTALLKERNEL
+export PAHOLE RESOLVE_BTFIDS BTF_OBJCOPY
 export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
 export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD TAR
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS KBUILD_PROCMACROLDFLAGS LDFLAGS_MODULE
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 60281c4f9e99..ec9e683244fa 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -391,6 +391,7 @@ config DEBUG_INFO_BTF
 	depends on PAHOLE_VERSION >= 122
 	# pahole uses elfutils, which does not have support for Hexagon relocations
 	depends on !HEXAGON
+	depends on $(success,command -v $(BTF_OBJCOPY))
 	help
 	  Generate deduplicated BTF type information from DWARF debug info.
 	  Turning this on requires pahole v1.22 or later, which will convert
diff --git a/scripts/gen-btf.sh b/scripts/gen-btf.sh
index 06c6d8becaa2..6ae671523edd 100755
--- a/scripts/gen-btf.sh
+++ b/scripts/gen-btf.sh
@@ -97,9 +97,9 @@ gen_btf_o()
 	# be redefined in the linker script.
 	info OBJCOPY "${btf_data}"
 	echo "" | ${CC} ${CLANG_FLAGS} -c -x c -o ${btf_data} -
-	${OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF \
+	${BTF_OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF \
 		--set-section-flags .BTF=alloc,readonly ${btf_data}
-	${OBJCOPY} --only-section=.BTF --strip-all ${btf_data}
+	${BTF_OBJCOPY} --only-section=.BTF --strip-all ${btf_data}
 
 	# Change e_type to ET_REL so that it can be used to link final vmlinux.
 	# GNU ld 2.35+ and lld do not allow an ET_EXEC input.
@@ -114,16 +114,16 @@ gen_btf_o()
 embed_btf_data()
 {
 	info OBJCOPY "${ELF_FILE}.BTF"
-	${OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF ${ELF_FILE}
+	${BTF_OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF ${ELF_FILE}
 
 	# a module might not have a .BTF_ids or .BTF.base section
 	local btf_base="${ELF_FILE}.BTF.base"
 	if [ -f "${btf_base}" ]; then
-		${OBJCOPY} --add-section .BTF.base=${btf_base} ${ELF_FILE}
+		${BTF_OBJCOPY} --add-section .BTF.base=${btf_base} ${ELF_FILE}
 	fi
 	local btf_ids="${ELF_FILE}.BTF_ids"
 	if [ -f "${btf_ids}" ]; then
-		${OBJCOPY} --update-section .BTF_ids=${btf_ids} ${ELF_FILE}
+		${BTF_OBJCOPY} --update-section .BTF_ids=${btf_ids} ${ELF_FILE}
 	fi
 }
 
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index e2207e612ac3..4ad04d31f8bc 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -266,7 +266,7 @@ vmlinux_link "${VMLINUX}"
 
 if is_enabled CONFIG_DEBUG_INFO_BTF; then
 	info OBJCOPY ${btfids_vmlinux}
-	${OBJCOPY} --update-section .BTF_ids=${btfids_vmlinux} ${VMLINUX}
+	${BTF_OBJCOPY} --update-section .BTF_ids=${btfids_vmlinux} ${VMLINUX}
 fi
 
 mksysmap "${VMLINUX}" System.map
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index f28a32b16ff0..e998cac975c1 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -4,7 +4,7 @@ include ../../../scripts/Makefile.arch
 include ../../../scripts/Makefile.include
 
 CXX ?= $(CROSS_COMPILE)g++
-OBJCOPY ?= $(CROSS_COMPILE)objcopy
+BTF_OBJCOPY ?= $(CROSS_COMPILE)objcopy
 
 CURDIR := $(abspath .)
 TOOLSDIR := $(abspath ../../..)
@@ -657,7 +657,7 @@ $(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o:			\
 	$$(if $$(TEST_NEEDS_BTFIDS),						\
 		$$(call msg,BTFIDS,$(TRUNNER_BINARY),$$@)			\
 		$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@;	\
-		$(OBJCOPY) --update-section .BTF_ids=$$@.BTF_ids $$@)
+		$(BTF_OBJCOPY) --update-section .BTF_ids=$$@.BTF_ids $$@)
 
 $(TRUNNER_TEST_OBJS:.o=.d): $(TRUNNER_OUTPUT)/%.test.d:			\
 			    $(TRUNNER_TESTS_DIR)/%.c			\
-- 
2.47.3




> 
>> Patching llvm-objcopy would be great, it should be done. But we are
>> still going to be stuck with making sure older LLVMs can build the kernel.
>> So even if they backport the fix to v21, it won't help us much, unfortunately.
> 
> 21.1.8 was the last planned 21.x release [2] so I think it is unlikely
> that a 21.1.9 would be released for this but we won't know until it is
> merged into main. Much agreed on handling the old versions.
> 
> [1]: https://lore.kernel.org/20251218175824.3122690-1-cmllamas@xxxxxxxxxx/
> [2]: https://discourse.llvm.org/t/llvm-21-1-8-released/89144
> 
> Cheers,
> Nathan