Re: [RFC PATCH net-next] tools/bpf: fix build with binutils >= 2.28

[Quentin Monnet]

Hi Roman, thanks for working on this!

2017-12-19 14:38 UTC+0000 ~ Roman Gushchin <guro@xxxxxx>
> Bpftool build is broken with binutils version 2.28 and later.
> The cause is commit 003ca0fd2286 ("Refactor disassembler selection")
> in the binutils repo, which changed the disassembler() function
> signature.
>
> Fix this by checking binutils version and use an appropriate
> disassembler() signature.
>
> Signed-off-by: Roman Gushchin <guro@xxxxxx>
> Cc: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> ---
>  tools/bpf/Makefile             | 6 ++++++
>  tools/bpf/bpf_jit_disasm.c     | 7 +++++++
>  tools/bpf/bpftool/Makefile     | 6 ++++++
>  tools/bpf/bpftool/jit_disasm.c | 5 +++++
>  4 files changed, 24 insertions(+)
>
> diff --git a/tools/bpf/Makefile b/tools/bpf/Makefile
> index 07a6697466ef..3fd32fd0daa1 100644
> --- a/tools/bpf/Makefile
> +++ b/tools/bpf/Makefile
> @@ -6,8 +6,14 @@ LEX = flex
>  YACC = bison
>  MAKE = make
>  
> +BINUTILS_VER := $(word 4, $(shell readelf -v | head -n 1))
> +BINUTILS_VER_MAJ := $(word 1, $(subst ., , $(subst -, , ${BINUTILS_VER})))
> +BINUTILS_VER_MIN := $(word 2, $(subst ., , $(subst -, , ${BINUTILS_VER})))
> +
>  CFLAGS += -Wall -O2
>  CFLAGS += -D__EXPORTED_HEADERS__ -I../../include/uapi -I../../include
> +CFLAGS += -DBINUTILS_VER_MAJ=${BINUTILS_VER_MAJ}
> +CFLAGS += -DBINUTILS_VER_MIN=${BINUTILS_VER_MIN}
>  
>  %.yacc.c: %.y
>  	$(YACC) -o $@ -d $<
> diff --git a/tools/bpf/bpf_jit_disasm.c b/tools/bpf/bpf_jit_disasm.c
> index 75bf526a0168..3ef7c8bdc0f3 100644
> --- a/tools/bpf/bpf_jit_disasm.c
> +++ b/tools/bpf/bpf_jit_disasm.c
> @@ -72,7 +72,14 @@ static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
>  
>  	disassemble_init_for_target(&info);
>  
> +#if (BINUTILS_VER_MAJ >= 2) && (BINUTILS_VER_MIN >= 28)
> +	disassemble = disassembler(bfd_get_arch(bfdf),
> +				   bfd_big_endian(bfdf),
> +				   bfd_get_mach(bfdf),
> +				   bfdf);
> +#else
>  	disassemble = disassembler(bfdf);
> +#endif
>  	assert(disassemble);
>  
>  	do {
> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 3f17ad317512..94ad51bf14b5 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -40,6 +40,12 @@ CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wshadow
>  CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/tools/include/uapi -I$(srctree)/tools/include -I$(srctree)/tools/lib/bpf -I$(srctree)/kernel/bpf/
>  LIBS = -lelf -lbfd -lopcodes $(LIBBPF)
>  
> +BINUTILS_VER := $(word 4, $(shell readelf -v | head -n 1))

This does not seem to be portable. I tried that on Ubuntu and `readelf
-v` returns "GNU readelf (GNU Binutils for Ubuntu) 2.26.1", and
BINUTILS_VER catches "Binutils".

> +BINUTILS_VER_MAJ := $(word 1, $(subst ., , $(subst -, , ${BINUTILS_VER})))
> +BINUTILS_VER_MIN := $(word 2, $(subst ., , $(subst -, , ${BINUTILS_VER})))
> +CFLAGS += -DBINUTILS_VER_MAJ=${BINUTILS_VER_MAJ}
> +CFLAGS += -DBINUTILS_VER_MIN=${BINUTILS_VER_MIN}
> +
>  INSTALL ?= install
>  RM ?= rm -f
>  
> diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
> index 1551d3918d4c..eaa7127e9eeb 100644
> --- a/tools/bpf/bpftool/jit_disasm.c
> +++ b/tools/bpf/bpftool/jit_disasm.c
> @@ -107,7 +107,12 @@ void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes)
>  
>  	disassemble_init_for_target(&info);
>  
> +#if (BINUTILS_VER_MAJ >= 2) && (BINUTILS_VER_MIN >= 28)
> +	disassemble = disassembler(bfd_get_arch(bfdf), bfd_big_endian(bfdf),
> +				   bfd_get_mach(bfdf), bfdf);
> +#else
>  	disassemble = disassembler(bfdf);
> +#endif
>  	assert(disassemble);
>  
>  	if (json_output)

I discussed this issue with Jakub recently, and one suggestion he had
was to look in tools/build/feature to add a new "feature", by trying to
compile short programs, for making the distinction between binutils
versions. It probably requires more work, but could be more robust than
parsing the version from the command line?

Best,
Quentin