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Date: Wed, 12 Jun 2024 22:01:35 +0200
From: Nicolas Schier <nicolas@fjasle.eu>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	Nathan Chancellor <nathan@kernel.org>
Subject: Re: [PATCH v3 1/3] kbuild: refactor variables in
 scripts/link-vmlinux.sh
Message-ID: <20240612-olive-swine-of-tact-4acb2b@lindesnes>
References: <20240610112657.602958-1-masahiroy@kernel.org>
 <20240610112657.602958-2-masahiroy@kernel.org>
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In-Reply-To: <20240610112657.602958-2-masahiroy@kernel.org>

On Mon, Jun 10, 2024 at 08:25:16PM +0900, Masahiro Yamada wrote:
> Clean up the variables in scripts/link-vmlinux.sh
> 
>  - Specify the extra objects directly in vmlinux_link()
>  - Move the AS rule to kallsyms()
>  - Set kallsymso and btf_vmlinux_bin_o where they are generated
>  - Remove unneeded variable, kallsymso_prev
>  - Introduce the btf_data variable
>  - Introduce the strip_debug flag instead of checking the output name
> 
> No functional change intended.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
> 
> Changes in v3:
>  - Use ${strip_debug} for cleanup
> 
>  scripts/link-vmlinux.sh | 67 +++++++++++++++++++++--------------------
>  1 file changed, 35 insertions(+), 32 deletions(-)
> 
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 518c70b8db50..3d9d7257143a 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -45,7 +45,6 @@ info()
>  
>  # Link of vmlinux
>  # ${1} - output file
> -# ${2}, ${3}, ... - optional extra .o files
>  vmlinux_link()
>  {
>  	local output=${1}
> @@ -90,7 +89,7 @@ vmlinux_link()
>  	ldflags="${ldflags} ${wl}--script=${objtree}/${KBUILD_LDS}"
>  
>  	# The kallsyms linking does not need debug symbols included.
> -	if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> +	if [ -n "${strip_debug}" ] ; then
>  		ldflags="${ldflags} ${wl}--strip-debug"
>  	fi
>  
> @@ -101,7 +100,7 @@ vmlinux_link()
>  	${ld} ${ldflags} -o ${output}					\
>  		${wl}--whole-archive ${objs} ${wl}--no-whole-archive	\
>  		${wl}--start-group ${libs} ${wl}--end-group		\
> -		$@ ${ldlibs}
> +		${kallsymso} ${btf_vmlinux_bin_o} ${ldlibs}
>  }
>  
>  # generate .BTF typeinfo from DWARF debuginfo
> @@ -110,6 +109,7 @@ vmlinux_link()
>  gen_btf()
>  {
>  	local pahole_ver
> +	local btf_data=${2}
>  
>  	if ! [ -x "$(command -v ${PAHOLE})" ]; then
>  		echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
> @@ -124,16 +124,16 @@ gen_btf()
>  
>  	vmlinux_link ${1}
>  
> -	info "BTF" ${2}
> +	info BTF "${btf_data}"
>  	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
>  
> -	# Create ${2} which contains just .BTF section but no symbols. Add
> +	# Create ${btf_data} which contains just .BTF section but no symbols. Add
>  	# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
>  	# deletes all symbols including __start_BTF and __stop_BTF, which will
>  	# be redefined in the linker script. Add 2>/dev/null to suppress GNU
>  	# objcopy warnings: "empty loadable segment detected at ..."
>  	${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> -		--strip-all ${1} ${2} 2>/dev/null
> +		--strip-all ${1} "${btf_data}" 2>/dev/null
>  	# Change e_type to ET_REL so that it can be used to link final vmlinux.
>  	# GNU ld 2.35+ and lld do not allow an ET_EXEC input.
>  	if is_enabled CONFIG_CPU_BIG_ENDIAN; then
> @@ -141,10 +141,12 @@ gen_btf()
>  	else
>  		et_rel='\1\0'
>  	fi
> -	printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
> +	printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 status=none
> +
> +	btf_vmlinux_bin_o=${btf_data}
>  }
>  
> -# Create ${2} .S file with all symbols from the ${1} object file
> +# Create ${2}.o file with all symbols from the ${1} object file
>  kallsyms()
>  {
>  	local kallsymopt;
> @@ -165,27 +167,25 @@ kallsyms()
>  		kallsymopt="${kallsymopt} --lto-clang"
>  	fi
>  
> -	info KSYMS ${2}
> -	scripts/kallsyms ${kallsymopt} ${1} > ${2}
> +	info KSYMS "${2}.S"
> +	scripts/kallsyms ${kallsymopt} "${1}" > "${2}.S"
> +
> +	info AS "${2}.o"
> +	${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
> +	      ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} -c -o "${2}.o" "${2}.S"
> +
> +	kallsymso=${2}.o
>  }
>  
>  # Perform one step in kallsyms generation, including temporary linking of
>  # vmlinux.
>  kallsyms_step()
>  {
> -	kallsymso_prev=${kallsymso}
>  	kallsyms_vmlinux=.tmp_vmlinux.kallsyms${1}
> -	kallsymso=${kallsyms_vmlinux}.o
> -	kallsyms_S=${kallsyms_vmlinux}.S
>  
> -	vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o}
> -	mksysmap ${kallsyms_vmlinux} ${kallsyms_vmlinux}.syms
> -	kallsyms ${kallsyms_vmlinux}.syms ${kallsyms_S}
> -
> -	info AS ${kallsymso}
> -	${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
> -	      ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
> -	      -c -o ${kallsymso} ${kallsyms_S}
> +	vmlinux_link "${kallsyms_vmlinux}"
> +	mksysmap "${kallsyms_vmlinux}" "${kallsyms_vmlinux}.syms"
> +	kallsyms "${kallsyms_vmlinux}.syms" "${kallsyms_vmlinux}"
>  }
>  
>  # Create map file with all symbols from ${1}
> @@ -223,19 +223,18 @@ fi
>  
>  ${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
>  
> -btf_vmlinux_bin_o=""
> +btf_vmlinux_bin_o=
> +kallsymso=
> +strip_debug=
> +
>  if is_enabled CONFIG_DEBUG_INFO_BTF; then
> -	btf_vmlinux_bin_o=.btf.vmlinux.bin.o
> -	if ! gen_btf .tmp_vmlinux.btf $btf_vmlinux_bin_o ; then
> +	if ! gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
>  		echo >&2 "Failed to generate BTF for vmlinux"
>  		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
>  		exit 1
>  	fi
>  fi
>  
> -kallsymso=""
> -kallsymso_prev=""
> -kallsyms_vmlinux=""
>  if is_enabled CONFIG_KALLSYMS; then
>  
>  	# kallsyms support
> @@ -261,11 +260,13 @@ if is_enabled CONFIG_KALLSYMS; then
>  	# a)  Verify that the System.map from vmlinux matches the map from
>  	#     ${kallsymso}.
>  
> -	kallsyms_step 1
> -	kallsyms_step 2
> +	# The kallsyms linking does not need debug symbols included.
> +	strip_debug=1
>  
> -	# step 3
> -	size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso_prev})
> +	kallsyms_step 1
> +	size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
> +
> +	kallsyms_step 2
>  	size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
>  
>  	if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
> @@ -273,7 +274,9 @@ if is_enabled CONFIG_KALLSYMS; then
>  	fi
>  fi
>  
> -vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
> +strip_debug=
> +
> +vmlinux_link vmlinux
>  
>  # fill in BTF IDs
>  if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
> -- 
> 2.43.0
> 
> 

Looks good to me.

Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>