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8050568e0a
A kernel build consists of more than one linking pass on vmlinux.o and
vmlinux, at minimum two, and with CONFIG_KALLSYMS and BTF enabled on x86-64
for example there are 5 such stages.
For architectures that build their own relocation tables (x86, riscv, mips,
s390), vmlinux is linked with the --emit-relocs parameter specified.
However, this is only required on the final vmlinux link.
Symbol tables of trial links preceding it don't need it because they
already check that System.map matches kallsyms symbols on each build.
GNU ld is slow at emitting relocation tables, so this results in a
reduction in build time.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 9.5s 9.1s -0.42s (-4%)
x86 defconfig, clean, gcc 30.1s 29.5s -0.59s (-2%)
x86 allmodconfig, touch mm/vma.c, gcc 37.2s 35.8s -1.4s (-4%)
Note that this has little impact on LLVM ld which performs this operation
more efficiently.
Assisted-by: LLM
Reviewed-by: Nicolas Schier <n.schier@fritz.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Link: https://patch.msgid.link/20260923-build-speedup-v4-6-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
321 lines
8.0 KiB
Bash
Executable File
321 lines
8.0 KiB
Bash
Executable File
#!/bin/sh
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# SPDX-License-Identifier: GPL-2.0
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#
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# link vmlinux
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#
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# vmlinux is linked from the objects in vmlinux.a and $(KBUILD_VMLINUX_LIBS).
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# vmlinux.a contains objects that are linked unconditionally.
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# $(KBUILD_VMLINUX_LIBS) are archives which are linked conditionally
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# (not within --whole-archive), and do not require symbol indexes added.
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#
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# vmlinux
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# ^
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# |
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# +--< vmlinux.a
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# |
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# +--< $(KBUILD_VMLINUX_LIBS)
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# | +--< lib/lib.a + more
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# |
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# +-< ${kallsymso} (see description in KALLSYMS section)
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#
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# vmlinux version (uname -v) cannot be updated during normal
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# descending-into-subdirs phase since we do not yet know if we need to
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# update vmlinux.
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# Therefore this step is delayed until just before final link of vmlinux.
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#
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# System.map is generated to document addresses of all kernel symbols
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# Error out on error
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set -e
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LD="$1"
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KBUILD_LDFLAGS="$2"
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LDFLAGS_vmlinux="$3"
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VMLINUX="$4"
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is_enabled() {
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grep -q "^$1=y" include/config/auto.conf
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}
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# Nice output in kbuild format
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# Will be suppressed by "make -s"
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info()
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{
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printf " %-7s %s\n" "${1}" "${2}"
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}
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# Link of vmlinux
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# ${1} - output file
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vmlinux_link()
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{
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local output=${1}
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local objs
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local libs
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local ld
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local ldflags
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local ldlibs
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info LD ${output}
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# skip output file argument
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shift
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if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT ||
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is_enabled CONFIG_KLP_BUILD; then
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# Use vmlinux.o instead of performing the slow LTO link again.
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objs=vmlinux.o
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libs=
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else
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objs=vmlinux.a
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libs="${KBUILD_VMLINUX_LIBS}"
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fi
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if is_enabled CONFIG_GENERIC_BUILTIN_DTB; then
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objs="${objs} .builtin-dtbs.o"
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fi
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objs="${objs} .vmlinux.export.o"
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objs="${objs} init/version-timestamp.o"
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if [ "${SRCARCH}" = "um" ]; then
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wl=-Wl,
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ld="${CC}"
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ldflags="${CFLAGS_vmlinux}"
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ldlibs="-lutil -lrt -lpthread"
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else
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wl=
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ld="${LD}"
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ldflags="${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux}"
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ldlibs=
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fi
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ldflags="${ldflags} ${wl}--script=${objtree}/${KBUILD_LDS}"
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# The kallsyms linking does not need debug symbols included.
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if [ -n "${strip_debug}" ] ; then
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ldflags="${ldflags} ${wl}--strip-debug"
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fi
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# Only the final link actually requires the relocations.
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if [ "${output}" = "${VMLINUX}" ] && is_enabled CONFIG_ARCH_VMLINUX_NEEDS_RELOCS; then
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ldflags="${ldflags} ${wl}--emit-relocs"
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fi
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if [ -n "${generate_map}" ]; then
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ldflags="${ldflags} ${wl}-Map=vmlinux.map"
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fi
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${ld} ${ldflags} -o ${output} \
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${wl}--whole-archive ${objs} ${wl}--no-whole-archive \
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${wl}--start-group ${libs} ${wl}--end-group \
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${kallsymso} ${btf_vmlinux_bin_o} ${arch_vmlinux_o} ${ldlibs}
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}
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# Check if kallsymso_prev and kallsymso differ
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# If symbol sizes within ${kallsymso} change, any symbols within vmlinux are
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# likely to shift, invalidating ${kallsymso}.
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# Since file size can remain unchanged even if symbol sizes change, compare the
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# actual symbols instead of relying on file size only.
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kallsymso_changed()
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{
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${NM} -n "${kallsymso_prev}" > "${kallsymso_prev}.sym"
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${NM} -n "${kallsymso}" > "${kallsymso}.sym"
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! cmp -s "${kallsymso_prev}.sym" "${kallsymso}.sym"
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}
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# Create ${2}.o file with all symbols from the ${1} object file
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kallsyms()
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{
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local kallsymopt;
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if is_enabled CONFIG_KALLSYMS_ALL; then
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kallsymopt="${kallsymopt} --all-symbols"
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fi
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if is_enabled CONFIG_64BIT || is_enabled CONFIG_RELOCATABLE; then
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kallsymopt="${kallsymopt} --pc-relative"
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fi
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info KSYMS "${2}.S"
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scripts/kallsyms ${kallsymopt} "${1}" "${2}.bin" > "${2}.S"
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info AS "${2}.o"
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${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
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${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} -c -o "${2}.o" "${2}.S"
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kallsymso_prev="${kallsymso:-}"
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kallsymso=${2}.o
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}
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# Perform kallsyms for the given temporary vmlinux.
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sysmap_and_kallsyms()
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{
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mksysmap "${1}" "${1}.syms"
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kallsyms "${1}.syms" "${1}.kallsyms"
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kallsyms_sysmap=${1}.syms
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}
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# Create map file with all symbols from ${1}
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# See mksymap for additional details
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mksysmap()
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{
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info NM ${2}
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${NM} -n "${1}" | sed -f "${srctree}/scripts/mksysmap" > "${2}"
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}
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sorttable()
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{
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${NM} -p -S ${1} > .tmp_vmlinux.nm-sort
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${objtree}/scripts/sorttable -s .tmp_vmlinux.nm-sort ${1}
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}
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cleanup()
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{
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rm -f .btf.*
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rm -f .tmp_vmlinux.nm-sort
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rm -f System.map
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rm -f vmlinux
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rm -f vmlinux.map
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}
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# Use "make V=1" to debug this script
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case "${KBUILD_VERBOSE}" in
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*1*)
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set -x
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;;
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esac
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if [ "$1" = "clean" ]; then
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cleanup
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exit 0
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fi
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${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
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arch_vmlinux_o=
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if is_enabled CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX; then
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arch_vmlinux_o=arch/${SRCARCH}/tools/vmlinux.arch.o
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fi
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btf_vmlinux_bin_o=
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btfids_vmlinux=
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kallsymso=
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strip_debug=
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generate_map=
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# Use "make UT=1" to trigger warnings on unused tracepoints
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case "${WARN_ON_UNUSED_TRACEPOINTS}" in
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*1*)
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${objtree}/scripts/tracepoint-update vmlinux.o
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;;
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esac
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if is_enabled CONFIG_KALLSYMS; then
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true > .tmp_vmlinux0.syms
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kallsyms .tmp_vmlinux0.syms .tmp_vmlinux0.kallsyms
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fi
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if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then
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# The kallsyms linking does not need debug symbols, but the BTF does.
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if ! is_enabled CONFIG_DEBUG_INFO_BTF; then
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strip_debug=1
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fi
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vmlinux_link .tmp_vmlinux1
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fi
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if is_enabled CONFIG_DEBUG_INFO_BTF; then
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info BTF .tmp_vmlinux1
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if ! ${CONFIG_SHELL} ${srctree}/scripts/gen-btf.sh .tmp_vmlinux1; then
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echo >&2 "Failed to generate BTF for vmlinux"
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echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
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exit 1
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fi
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btf_vmlinux_bin_o=.tmp_vmlinux1.btf.o
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btfids_vmlinux=.tmp_vmlinux1.BTF_ids
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fi
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if is_enabled CONFIG_KALLSYMS; then
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# kallsyms support
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# Generate section listing all symbols and add it into vmlinux
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# It's a four step process:
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# 0) Generate a dummy __kallsyms with empty symbol list.
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# 1) Link .tmp_vmlinux1.kallsyms so it has all symbols and sections,
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# with a dummy __kallsyms.
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# Running kallsyms on that gives us .tmp_vmlinux1.kallsyms.o with
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# the right size
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# 2) Link .tmp_vmlinux2.kallsyms so it now has a __kallsyms section of
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# the right size, but due to the added section, some
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# addresses have shifted.
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# From here, we generate a correct .tmp_vmlinux2.kallsyms.o
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# 3) That link may have expanded the kernel image enough that
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# more linker branch stubs / trampolines had to be added, which
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# introduces new names, which further expands kallsyms. Do another
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# pass if that is the case. In theory it's possible this results
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# in even more stubs, but unlikely.
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# KALLSYMS_EXTRA_PASS=1 may also used to debug or work around
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# other bugs.
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# 4) The correct ${kallsymso} is linked into the final vmlinux.
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#
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# a) Verify that the System.map from vmlinux matches the map from
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# ${kallsymso}.
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# The kallsyms linking does not need debug symbols included.
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strip_debug=1
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sysmap_and_kallsyms .tmp_vmlinux1
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size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
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vmlinux_link .tmp_vmlinux2
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sysmap_and_kallsyms .tmp_vmlinux2
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size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
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# Due to alignment, file size of the kallsymso object file might remain
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# unchanged even if individual symbols within change size. Changed
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# symbol sizes can still shift other symbols, though. Therefore, don't
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# rely on file size alone.
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if [ $size1 -ne $size2 ] || kallsymso_changed || \
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[ -n "${KALLSYMS_EXTRA_PASS}" ]; then
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vmlinux_link .tmp_vmlinux3
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sysmap_and_kallsyms .tmp_vmlinux3
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fi
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fi
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strip_debug=
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if is_enabled CONFIG_VMLINUX_MAP; then
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generate_map=1
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fi
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vmlinux_link "${VMLINUX}"
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if is_enabled CONFIG_DEBUG_INFO_BTF; then
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info BTFIDS ${VMLINUX}
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${RESOLVE_BTFIDS} --patch_btfids ${btfids_vmlinux} ${VMLINUX}
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fi
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mksysmap "${VMLINUX}" System.map
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if is_enabled CONFIG_BUILDTIME_TABLE_SORT; then
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info SORTTAB "${VMLINUX}"
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if ! sorttable "${VMLINUX}"; then
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echo >&2 Failed to sort kernel tables
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exit 1
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fi
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fi
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# step a (see comment above)
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if is_enabled CONFIG_KALLSYMS; then
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if ! cmp -s System.map "${kallsyms_sysmap}"; then
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echo >&2 Inconsistent kallsyms data
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echo >&2 'Try "make KALLSYMS_EXTRA_PASS=1" as a workaround'
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exit 1
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fi
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fi
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# For fixdep
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echo "${VMLINUX}: $0" > ".${VMLINUX}.d"
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