Re: [PATCHv2 bpf-next] kbuild: Unify options for BTF generation for vmlinux and modules

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Oct 26, 2021 at 11:24:19PM +0200, Jiri Olsa wrote:
> Using new PAHOLE_FLAGS variable to pass extra arguments to
> pahole for both vmlinux and modules BTF data generation.
> 
> Adding new scripts/pahole-flags.sh script that detect and
> prints pahole options.
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

I'm checking on reported build failures and will send v3

jirka

> ---
> v2 changes:
>   - posting separately from original patchset
>   - added Andrii's ack
> 
>  Makefile                  |  3 +++
>  scripts/Makefile.modfinal |  2 +-
>  scripts/link-vmlinux.sh   | 11 +----------
>  scripts/pahole-flags.sh   | 20 ++++++++++++++++++++
>  4 files changed, 25 insertions(+), 11 deletions(-)
>  create mode 100755 scripts/pahole-flags.sh
> 
> diff --git a/Makefile b/Makefile
> index 437ccc66a1c2..ee514b80c62e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -480,6 +480,8 @@ LZ4		= lz4c
>  XZ		= xz
>  ZSTD		= zstd
>  
> +PAHOLE_FLAGS	= $(shell PAHOLE=$(PAHOLE) scripts/pahole-flags.sh)
> +
>  CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
>  		  -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)
>  NOSTDINC_FLAGS :=
> @@ -534,6 +536,7 @@ export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
>  export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
>  export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
>  export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
> +export PAHOLE_FLAGS
>  
>  # Files to ignore in find ... statements
>  
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 1fb45b011e4b..7f39599e9fae 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -40,7 +40,7 @@ quiet_cmd_ld_ko_o = LD [M]  $@
>  quiet_cmd_btf_ko = BTF [M] $@
>        cmd_btf_ko = 							\
>  	if [ -f vmlinux ]; then						\
> -		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J --btf_base vmlinux $@; \
> +		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \
>  		$(RESOLVE_BTFIDS) -b vmlinux $@; 			\
>  	else								\
>  		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index d74cee5c4326..3ea7cece7c97 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -205,7 +205,6 @@ vmlinux_link()
>  gen_btf()
>  {
>  	local pahole_ver
> -	local extra_paholeopt=
>  
>  	if ! [ -x "$(command -v ${PAHOLE})" ]; then
>  		echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
> @@ -220,16 +219,8 @@ gen_btf()
>  
>  	vmlinux_link ${1}
>  
> -	if [ "${pahole_ver}" -ge "118" ] && [ "${pahole_ver}" -le "121" ]; then
> -		# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
> -		extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_vars"
> -	fi
> -	if [ "${pahole_ver}" -ge "121" ]; then
> -		extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
> -	fi
> -
>  	info "BTF" ${2}
> -	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${extra_paholeopt} ${1}
> +	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
>  
>  	# Create ${2} which contains just .BTF section but no symbols. Add
>  	# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> new file mode 100755
> index 000000000000..2b99fc77019c
> --- /dev/null
> +++ b/scripts/pahole-flags.sh
> @@ -0,0 +1,20 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +
> +extra_paholeopt=
> +
> +if ! [ -x "$(command -v ${PAHOLE})" ]; then
> +	return
> +fi
> +
> +pahole_ver=$(${PAHOLE} --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/')
> +
> +if [ "${pahole_ver}" -ge "118" ] && [ "${pahole_ver}" -le "121" ]; then
> +	# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
> +	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_vars"
> +fi
> +if [ "${pahole_ver}" -ge "121" ]; then
> +	extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
> +fi
> +
> +echo ${extra_paholeopt}
> -- 
> 2.31.1
>