Commit b1a9a5e0 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: merge temporary vmlinux for BTF and kallsyms 



CONFIG_DEBUG_INFO_BTF=y requires one additional link step.
(.tmp_vmlinux.btf)

CONFIG_KALLSYMS=y requires two additional link steps.
(.tmp_vmlinux.kallsyms1 and .tmp_vmlinux.kallsyms2)

Enabling both requires three additional link steps.

When CONFIG_DEBUG_INFO_BTF=y and CONFIG_KALLSYMS=y, the current build
process is as follows:

    KSYMS   .tmp_vmlinux.kallsyms0.S
    AS      .tmp_vmlinux.kallsyms0.o
    LD      .tmp_vmlinux.btf             # temporary vmlinux for BTF
    BTF     .btf.vmlinux.bin.o
    LD      .tmp_vmlinux.kallsyms1       # temporary vmlinux for kallsyms step 1
    NM      .tmp_vmlinux.kallsyms1.syms
    KSYMS   .tmp_vmlinux.kallsyms1.S
    AS      .tmp_vmlinux.kallsyms1.o
    LD      .tmp_vmlinux.kallsyms2       # temporary vmlinux for kallsyms step 2
    NM      .tmp_vmlinux.kallsyms2.syms
    KSYMS   .tmp_vmlinux.kallsyms2.S
    AS      .tmp_vmlinux.kallsyms2.o
    LD      vmlinux                      # final vmlinux

This is redundant because the BTF generation and the kallsyms step 1 can
be performed against the same temporary vmlinux.

When both CONFIG_DEBUG_INFO_BTF and CONFIG_KALLSYMS are enabled, we can
reduce the number of link steps by one.

This commit changes the build process as follows:

    KSYMS   .tmp_vmlinux0.kallsyms.S
    AS      .tmp_vmlinux0.kallsyms.o
    LD      .tmp_vmlinux1                # temporary vmlinux for BTF and kallsyms step 1
    BTF     .tmp_vmlinux1.btf.o
    NM      .tmp_vmlinux1.syms
    KSYMS   .tmp_vmlinux1.kallsyms.S
    AS      .tmp_vmlinux1.kallsyms.o
    LD      .tmp_vmlinux2                # temporary vmlinux for kallsyms step 2
    NM      .tmp_vmlinux2.syms
    KSYMS   .tmp_vmlinux2.kallsyms.S
    AS      .tmp_vmlinux2.kallsyms.o
    LD      vmlinux                      # final vmlinux

Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
parent c442db3f

scripts/link-vmlinux.sh

+24 −17
Original line number Diff line number Diff line
@@ -105,11 +105,10 @@ vmlinux_link() 


# generate .BTF typeinfo from DWARF debuginfo

# ${1} - vmlinux image

# ${2} - file to dump raw BTF data into

gen_btf()

{

	local pahole_ver

	local btf_data=${2}

	local btf_data=${1}.btf.o



	if ! [ -x "$(command -v ${PAHOLE})" ]; then

		echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
@@ -122,8 +121,6 @@ gen_btf() 
		return 1

	fi



	vmlinux_link ${1}



	info BTF "${btf_data}"

	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
@@ -177,15 +174,13 @@ kallsyms() 
	kallsymso=${2}.o

}



# Perform one step in kallsyms generation, including temporary linking of

# vmlinux.

kallsyms_step()

# Perform kallsyms for the given temporary vmlinux.

sysmap_and_kallsyms()

{

	kallsyms_vmlinux=.tmp_vmlinux.kallsyms${1}

	mksysmap "${1}" "${1}.syms"

	kallsyms "${1}.syms" "${1}.kallsyms"



	vmlinux_link "${kallsyms_vmlinux}"

	mksysmap "${kallsyms_vmlinux}" "${kallsyms_vmlinux}.syms"

	kallsyms "${kallsyms_vmlinux}.syms" "${kallsyms_vmlinux}"

	kallsyms_sysmap=${1}.syms

}



# Create map file with all symbols from ${1}
@@ -228,11 +223,21 @@ kallsymso= 
strip_debug=



if is_enabled CONFIG_KALLSYMS; then

	kallsyms /dev/null .tmp_vmlinux.kallsyms0

	kallsyms /dev/null .tmp_vmlinux0.kallsyms

fi



if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then



	# The kallsyms linking does not need debug symbols, but the BTF does.

	if ! is_enabled CONFIG_DEBUG_INFO_BTF; then

		strip_debug=1

	fi



	vmlinux_link .tmp_vmlinux1

fi



if is_enabled CONFIG_DEBUG_INFO_BTF; then

	if ! gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then

	if ! gen_btf .tmp_vmlinux1; then

		echo >&2 "Failed to generate BTF for vmlinux"

		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"

		exit 1
@@ -268,14 +273,16 @@ if is_enabled CONFIG_KALLSYMS; then 
	# The kallsyms linking does not need debug symbols included.

	strip_debug=1



	kallsyms_step 1

	sysmap_and_kallsyms .tmp_vmlinux1

	size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})



	kallsyms_step 2

	vmlinux_link .tmp_vmlinux2

	sysmap_and_kallsyms .tmp_vmlinux2

	size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})



	if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then

		kallsyms_step 3

		vmlinux_link .tmp_vmlinux3

		sysmap_and_kallsyms .tmp_vmlinux3

	fi

fi
@@ -301,7 +308,7 @@ fi 


# step a (see comment above)

if is_enabled CONFIG_KALLSYMS; then

	if ! cmp -s System.map ${kallsyms_vmlinux}.syms; then

	if ! cmp -s System.map "${kallsyms_sysmap}"; then

		echo >&2 Inconsistent kallsyms data

		echo >&2 'Try "make KALLSYMS_EXTRA_PASS=1" as a workaround'

		exit 1