[PATCH v2 bpf-next 13/18] kbuild: Add support for BTF inline information

[Alan Maguire <alan.maguire@oracle.com>]

Add CONFIG_DEBUG_INFO_BTF_INLINE to generate BTF inline-location
information with pahole v1.31 and later.

Enable pahole's inline feature and pass --inline to resolve_btfids.
This extracts LOC_PARAM, LOC_PROTO, and LOCSEC types into a split BTF
blob named <output>.BTF.inline while the ordinary BTF remains in .BTF.

Embed the resulting blob in a .BTF.inline ELF section for vmlinux and
modules.  Add the vmlinux linker-script output section to avoid it
being treated as an orphan.

Use the inline pahole feature unconditionally for both in-tree and
external modules; the generated split BTF has the same format in both
cases.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 include/asm-generic/vmlinux.lds.h | 11 +++++++++++
 lib/Kconfig.debug                 | 17 +++++++++++++++++
 scripts/Makefile.btf              |  7 +++++++
 scripts/gen-btf.sh                | 17 +++++++++++++++--
 4 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2988aa12f66..a2e192854c47 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -675,12 +675,23 @@
 /*
  * .BTF
  */
+#ifdef CONFIG_DEBUG_INFO_BTF_INLINE
+#define BTF_INLINE							\
+	. = ALIGN(PAGE_SIZE);						\
+	.BTF.inline : AT(ADDR(.BTF.inline) - LOAD_OFFSET) {		\
+		BOUNDED_SECTION_BY(.BTF.inline, _BTF_inline)		\
+	}
+#else
+#define BTF_INLINE
+#endif
+
 #ifdef CONFIG_DEBUG_INFO_BTF
 #define BTF								\
 	. = ALIGN(PAGE_SIZE);						\
 	.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {				\
 		BOUNDED_SECTION_BY(.BTF, _BTF)				\
 	}								\
+	BTF_INLINE							\
 	. = ALIGN(PAGE_SIZE);						\
 	.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) {			\
 		*(.BTF_ids)						\
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1244dcac2294..dd1b2d9ebe99 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -425,6 +425,12 @@ config PAHOLE_HAS_LANG_EXCLUDE
 	  otherwise it would emit malformed kernel and module binaries when
 	  using DEBUG_INFO_BTF_MODULES.
 
+config PAHOLE_HAS_INLINE
+	def_bool PAHOLE_VERSION >= 131
+	help
+	  Support for the "inline" BTF feature is available. It encodes
+	  information about inline sites and how to retrieve their parameters.
+
 config DEBUG_INFO_BTF_MODULES
 	bool "Generate BTF type information for kernel modules"
 	default y
@@ -432,6 +438,17 @@ config DEBUG_INFO_BTF_MODULES
 	help
 	  Generate compact split BTF type information for kernel modules.
 
+config DEBUG_INFO_BTF_INLINE
+	bool "Provide information about inline sites in BTF"
+	default n
+	depends on DEBUG_INFO_BTF && PAHOLE_HAS_INLINE && SYSFS
+	help
+	  Generate information about inline sites in .BTF.inline sections.
+	  These sections contain split BTF relative to the kernel or module BTF
+	  and are made available in /sys/kernel/btf with a ".inline" suffix.
+	  The information describes inline locations and how to retrieve their
+	  associated parameters.
+
 config MODULE_ALLOW_BTF_MISMATCH
 	bool "Allow loading modules with non-matching BTF type info"
 	depends on DEBUG_INFO_BTF_MODULES
diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index a1812985a61a..d42dbc8d7199 100644
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -22,7 +22,14 @@ endif
 
 pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
 
+btf-inline := $(CONFIG_DEBUG_INFO_BTF_INLINE)
+ifneq ($(btf-inline),)
+btf-inline-feat := inline
+pahole-flags-$(call test-ge, $(pahole-ver), 131) += --btf_features=$(btf-inline-feat)
+endif
+
 export PAHOLE_FLAGS := $(pahole-flags-y)
+export BTF_INLINE := $(btf-inline)
 
 resolve-btfids-flags-y :=
 resolve-btfids-flags-$(CONFIG_WERROR) += --fatal_warnings
diff --git a/scripts/gen-btf.sh b/scripts/gen-btf.sh
index 8ca96eb10a69..a75f41878c32 100755
--- a/scripts/gen-btf.sh
+++ b/scripts/gen-btf.sh
@@ -76,6 +76,7 @@ gen_btf_data()
 
 	${RESOLVE_BTFIDS} ${RESOLVE_BTFIDS_FLAGS}	\
 		${BTF_BASE:+--btf_base ${BTF_BASE}}	\
+		${BTF_INLINE:+--inline}		\
 		--btf ${btf1} "${ELF_FILE}"
 }
 
@@ -83,14 +84,21 @@ gen_btf_o()
 {
 	btf_data=${ELF_FILE}.btf.o
 
-	# Create ${btf_data} which contains just .BTF section but no symbols. Add
+	# Create ${btf_data} which contains just BTF sections but no symbols. Add
 	# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
 	# deletes all symbols including __start_BTF and __stop_BTF, which will
 	# be redefined in the linker script.
 	echo "" | ${CC} ${CLANG_FLAGS} ${KBUILD_CPPFLAGS} ${KBUILD_CFLAGS} -fno-lto -c -x c -o ${btf_data} -
 	${OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF \
 		--set-section-flags .BTF=alloc,readonly ${btf_data}
-	${OBJCOPY} --only-section=.BTF --strip-all ${btf_data}
+	ONLY_SEC="--only-section=.BTF"
+	btf_inline=${ELF_FILE}.BTF.inline
+	if [ -n "${BTF_INLINE}" ] && [ -f "${btf_inline}" ]; then
+		${OBJCOPY} --add-section .BTF.inline=${btf_inline} \
+			--set-section-flags .BTF.inline=alloc,readonly ${btf_data}
+		ONLY_SEC="${ONLY_SEC} --only-section=.BTF.inline"
+	fi
+	${OBJCOPY} ${ONLY_SEC} --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.
@@ -111,6 +119,10 @@ embed_btf_data()
 	if [ -f "${btf_base}" ]; then
 		${OBJCOPY} --add-section .BTF.base=${btf_base} ${ELF_FILE}
 	fi
+	btf_inline=${ELF_FILE}.BTF.inline
+	if [ -n "${BTF_INLINE}" ] && [ -f "${btf_inline}" ]; then
+		${OBJCOPY} --add-section .BTF.inline=${btf_inline} ${ELF_FILE}
+	fi
 	btf_ids="${ELF_FILE}.BTF_ids"
 	if [ -f "${btf_ids}" ]; then
 		${RESOLVE_BTFIDS} --patch_btfids ${btf_ids} ${ELF_FILE}
@@ -121,6 +133,7 @@ cleanup()
 {
 	rm -f "${ELF_FILE}.BTF.1"
 	rm -f "${ELF_FILE}.BTF"
+	rm -f "${ELF_FILE}.BTF.inline"
 	if [ "${BTFGEN_MODE}" = "module" ]; then
 		rm -f "${ELF_FILE}.BTF.base"
 		rm -f "${ELF_FILE}.BTF_ids"
-- 
2.43.5