Commit e83b9f55 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann

kbuild: add ability to generate BTF type info for vmlinux

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: default avatarAndrii Nakryiko <andriin@fb.com>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 99182bee
......@@ -399,6 +399,7 @@ NM = $(CROSS_COMPILE)nm
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
PAHOLE = pahole
LEX = flex
YACC = bison
AWK = awk
......@@ -453,7 +454,7 @@ KBUILD_LDFLAGS :=
GCC_PLUGINS_CFLAGS :=
export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
export CPP AR NM STRIP OBJCOPY OBJDUMP KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS
export CPP AR NM STRIP OBJCOPY OBJDUMP PAHOLE KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS
export MAKE LEX YACC AWK INSTALLKERNEL PERL PYTHON PYTHON2 PYTHON3 UTS_MACHINE
export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
......
......@@ -219,6 +219,14 @@ config DEBUG_INFO_DWARF4
But it significantly improves the success of resolving
variables in gdb on optimized code.
config DEBUG_INFO_BTF
bool "Generate BTF typeinfo"
depends on DEBUG_INFO
help
Generate deduplicated BTF type information from DWARF debug info.
Turning this on expects presence of pahole tool, which will convert
DWARF type info into equivalent deduplicated BTF type info.
config GDB_SCRIPTS
bool "Provide GDB scripts for kernel debugging"
depends on DEBUG_INFO
......
......@@ -35,7 +35,7 @@ set -e
info()
{
if [ "${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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