kbuild: add ability to generate BTF type info for vmlinux (e83b9f55) · Commits · 戴 / test

This patch adds new config option to trigger generation of BTF type information from DWARF debuginfo for vmlinux and kernel modules through pahole, which in turn relies on libbpf for btf_dedup() algorithm. The intent is to record compact type information of all types used inside kernel, including all the structs/unions/typedefs/etc. This enables BPF's compile-once-run-everywhere ([0]) approach, in which tracing programs that are inspecting kernel's internal data (e.g., struct task_struct) can be compiled on a system running some kernel version, but would be possible to run on other kernel versions (and configurations) without recompilation, even if the layout of structs changed and/or some of the fields were added, removed, or renamed. This is only possible if BPF loader can get kernel type info to adjust all the offsets correctly. This patch is a first time in this direction, making sure that BTF type info is part of Linux kernel image in non-loadable ELF section. BTF deduplication ([1]) algorithm typically provides 100x savings compared to DWARF data, so resulting .BTF section is not big as is typically about 2MB in size. [0] http://vger.kernel.org/lpc-bpf2018.html#session-2 [1] https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Alexei Starovoitov <ast@fb.com> Cc: Yonghong Song <yhs@fb.com> Cc: Martin KaFai Lau <kafai@fb.com> Signed-off-by:

Andrii Nakryiko <andriin@fb.com> Acked-by:

David S. Miller <davem@davemloft.net> Acked-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Daniel Borkmann <daniel@iogearbox.net> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net>

Makefile

+2 −1

Original line number	Diff line number	Diff line
		@@ -399,6 +399,7 @@ NM = $(CROSS_COMPILE)nm
		STRIP = $(CROSS_COMPILE)strip
		OBJCOPY = $(CROSS_COMPILE)objcopy
		OBJDUMP = $(CROSS_COMPILE)objdump
		PAHOLE = pahole
		LEX = flex
		YACC = bison
		AWK = awk
		@@ -453,7 +454,7 @@ KBUILD_LDFLAGS :=
		GCC_PLUGINS_CFLAGS :=

		export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
		export CPP AR NM STRIP OBJCOPY OBJDUMP KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS
		export CPP AR NM STRIP OBJCOPY OBJDUMP PAHOLE KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS
		export MAKE LEX YACC AWK INSTALLKERNEL PERL PYTHON PYTHON2 PYTHON3 UTS_MACHINE
		export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS

lib/Kconfig.debug

+8 −0

Original line number	Diff line number	Diff line
		@@ -219,6 +219,14 @@ config DEBUG_INFO_DWARF4
		But it significantly improves the success of resolving
		variables in gdb on optimized code.

		config DEBUG_INFO_BTF
		bool "Generate BTF typeinfo"
		depends on DEBUG_INFO
		help
		Generate deduplicated BTF type information from DWARF debug info.
		Turning this on expects presence of pahole tool, which will convert
		DWARF type info into equivalent deduplicated BTF type info.

		config GDB_SCRIPTS
		bool "Provide GDB scripts for kernel debugging"
		depends on DEBUG_INFO

scripts/link-vmlinux.sh

+19 −1

Original line number	Diff line number	Diff line
		@@ -35,7 +35,7 @@ set -e
		info()
		{
		if [ "${quiet}" != "silent_" ]; then
		printf " %-7s %s\n" ${1} ${2}
		printf " %-7s %s\n" "${1}" "${2}"
		fi
		}

		@@ -91,6 +91,20 @@ vmlinux_link()
		fi
		}

		# generate .BTF typeinfo from DWARF debuginfo
		gen_btf()
		{
		local pahole_ver;

		pahole_ver=$(${PAHOLE} --version \| sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/')
		if [ "${pahole_ver}" -lt "113" ]; then
		info "BTF" "${1}: pahole version $(${PAHOLE} --version) is too old, need at least v1.13"
		exit 0
		fi

		info "BTF" ${1}
		LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
		}

		# Create ${2} .o file with all symbols from the ${1} object file
		kallsyms()
		@@ -248,6 +262,10 @@ fi
		info LD vmlinux
		vmlinux_link "${kallsymso}" vmlinux

		if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
		gen_btf vmlinux
		fi

		if [ -n "${CONFIG_BUILDTIME_EXTABLE_SORT}" ]; then
		info SORTEX vmlinux
		sortextable vmlinux

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