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Date: Wed, 3 Apr 2019 10:46:19 +0200
From: Jiri Olsa <jolsa@...hat.com>
To: andrii.nakryiko@...il.com
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, kernel-team@...com,
Andrii Nakryiko <andriin@...com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...com>, Yonghong Song <yhs@...com>,
Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next] kbuild: add ability to generate BTF type info
for vmlinux
On Tue, Apr 02, 2019 at 09:49:50AM -0700, andrii.nakryiko@...il.com wrote:
> From: Andrii Nakryiko <andriin@...com>
>
> 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.
hi,
I'm using the latest pahole from git tree:
https://github.com/acmel/dwarves.git
and getting pahole crash:
LD vmlinux
BTF vmlinux
die__process_inline_expansion: DW_TAG_label (0xa) @ <0x3eef8> not handled!
scripts/link-vmlinux.sh: line 96: 31222 Segmentation fault (core dumped) LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
make[1]: *** [/home/jolsa/linux/Makefile:1025: vmlinux] Error 139
make: *** [Makefile:170: sub-make] Error 2
is there some other source/dependency I'm missing?
thanks,
jirka
>
> [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@...ionext.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Alexei Starovoitov <ast@...com>
> Cc: Yonghong Song <yhs@...com>
> Cc: Martin KaFai Lau <kafai@...com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> 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
> --
> 2.17.1
>
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