Commit 3e86e4d74c ("kbuild: keep .modinfo section in vmlinux.unstripped")
placed MODULE_INFO() strings in the .modinfo section in vmlinux.unstripped,
however it left the section allocatable, so it gets assigned an address and
on arm64, arm and riscv, the section is tagged as PT_LOAD.
This is useless as the data is ultimately stripped anyway.
Doing this results in a lot of unnecessary work - each pass copies the
whole file, 450 MiB with relocations for an x86 allmodconfig build and 250
MiB for an arm64 allmodconfig build.
This adds ~0.7s on the serial tail of every build for arm64 and ~0.2s for
x86 (the tail is single-threaded work done after parallel work has
finished).
Nothing requires .modinfo to exist at an address, so mark the output
section (INFO) so that it's not allocated and use --dump-section to extract
it as -O only emits allocated sections.
The dump doesn't pick up the arch's OBJCOPYFLAGS any longer as they should
not impact the output of this section.
Image, bzImage, System.map and modules.builtin.modinfo are unchanged and
the stripped vmlinux differs only in its program headers.
The objcopy passes are on the serial tail of every build that links
vmlinux, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 11.2s 11.1s -0.15s (-1%)
x86 defconfig, touch mm/vma.c, clang 11.3s 11.1s -0.19s (-2%)
x86 defconfig, clean, gcc 32.5s 32.3s -0.16s (-1%)
x86 defconfig, clean, clang 34.5s 34.2s -0.26s (-1%)
x86 allmodconfig, touch mm/vma.c, gcc 40.1s 39.7s -0.44s (-1%)
Assisted-by: LLM
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@fritz.com>
Link: https://patch.msgid.link/20260923-build-speedup-v4-1-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
5fe4dd5966