On 3/15/19 1:17 PM, Andrii Nakryiko wrote: > 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@xxxxxxxxxxxxx> Masahiro, could you please review this patch? It's been pending for 10 days! Thanks > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> > Cc: Alexei Starovoitov <ast@xxxxxx> > Cc: Yonghong Song <yhs@xxxxxx> > Cc: Martin KaFai Lau <kafai@xxxxxx> > Signed-off-by: Andrii Nakryiko <andriin@xxxxxx> > --- > Makefile | 3 ++- > lib/Kconfig.debug | 8 ++++++++ > scripts/link-vmlinux.sh | 20 +++++++++++++++++++- > 3 files changed, 29 insertions(+), 2 deletions(-) > > diff --git a/Makefile b/Makefile > index d5713e7b1e50..a55308147a09 100644 > --- a/Makefile > +++ b/Makefile > @@ -387,6 +387,7 @@ NM = $(CROSS_COMPILE)nm > STRIP = $(CROSS_COMPILE)strip > OBJCOPY = $(CROSS_COMPILE)objcopy > OBJDUMP = $(CROSS_COMPILE)objdump > +PAHOLE = pahole > LEX = flex > YACC = bison > AWK = awk > @@ -442,7 +443,7 @@ KBUILD_LDFLAGS := > GCC_PLUGINS_CFLAGS := > > export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC > -export CPP AR NM STRIP OBJCOPY OBJDUMP KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS > +export CPP AR NM STRIP OBJCOPY OBJDUMP PAHOLE KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS > export MAKE LEX YACC AWK GENKSYMS INSTALLKERNEL PERL PYTHON PYTHON2 PYTHON3 UTS_MACHINE > export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index d4df5b24d75e..cce78dcd19a2 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -200,6 +200,14 @@ config DEBUG_INFO_DWARF4 > But it significantly improves the success of resolving > variables in gdb on optimized code. > > +config DEBUG_INFO_BTF > + bool "Generate BTF typeinfo" > + depends on DEBUG_INFO > + help > + Generate deduplicated BTF type information from DWARF debug info. > + Turning this on expects presence of pahole tool, which will convert > + DWARF type info into equivalent deduplicated BTF type info. > + > config GDB_SCRIPTS > bool "Provide GDB scripts for kernel debugging" > depends on DEBUG_INFO > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index c8cf45362bd6..73bb7dfdc2c9 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -40,7 +40,7 @@ set -e > info() > { > if [ "${quiet}" != "silent_" ]; then > - printf " %-7s %s\n" ${1} ${2} > + printf " %-7s %s\n" "${1}" "${2}" > fi > } > > @@ -114,6 +114,20 @@ vmlinux_link() > fi > } > > +# generate .BTF typeinfo from DWARF debuginfo > +gen_btf() > +{ > + local pahole_ver; > + > + pahole_ver=$(${PAHOLE} --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/') > + if [ "${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 ${1} object file > kallsyms() > @@ -281,6 +295,10 @@ fi > info LD vmlinux > vmlinux_link "${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 >
