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kbuild: Sync kconfig when PAHOLE_VERSION changes

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This patch implements kconfig re-sync when the pahole version changes
between builds, similar to how it happens for compiler version change
via CC_VERSION_TEXT.

Define PAHOLE_VERSION in the top-level Makefile and export it for
config builds. Set CONFIG_PAHOLE_VERSION default to the exported
variable.

Kconfig records the PAHOLE_VERSION value in
include/config/auto.conf.cmd [1].

The Makefile includes auto.conf.cmd, so if PAHOLE_VERSION changes
between builds, make detects a dependency change and triggers
syncconfig to update the kconfig [2].

For external module builds, add a warning message in the prepare
target, similar to the existing compiler version mismatch warning.

Note that if pahole is not installed or available, PAHOLE_VERSION is
set to 0 by pahole-version.sh, so the (un)installation of pahole is
treated as a version change.

See previous discussions for context [3].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/kconfig/preprocess.c?h=v6.18#n91
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Makefile?h=v6.18#n815
[3] https://lore.kernel.org/bpf/8f946abf-dd88-4fac-8bb4-84fcd8d81cf0@oracle.com/

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Nicolas Schier <nsc@kernel.org>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Link: https://lore.kernel.org/bpf/20251219181321.1283664-6-ihor.solodrai@linux.dev
This commit is contained in:
Ihor Solodrai 2025-12-19 10:13:18 -08:00 • committed by Andrii Nakryiko
parent fb348d4fdf
commit 90e5b38a26
2 changed files with 12 additions and 5 deletions
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15
Makefile
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@ -708,11 +708,12 @@ endif
# The expansion should be delayed until arch/$(SRCARCH)/Makefile is included.
# Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile.
# CC_VERSION_TEXT and RUSTC_VERSION_TEXT are referenced from Kconfig (so they
# need export), and from include/config/auto.conf.cmd to detect the compiler
# upgrade.
# CC_VERSION_TEXT, RUSTC_VERSION_TEXT and PAHOLE_VERSION are referenced from
# Kconfig (so they need export), and from include/config/auto.conf.cmd to
# detect the version changes between builds.
CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
RUSTC_VERSION_TEXT = $(subst $(pound),,$(shell $(RUSTC) --version 2>/dev/null))
PAHOLE_VERSION = $(shell $(srctree)/scripts/pahole-version.sh $(PAHOLE))
ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
include $(srctree)/scripts/Makefile.clang
@ -733,7 +734,7 @@ ifdef config-build
# KBUILD_DEFCONFIG may point out an alternative default configuration
# used for 'make defconfig'
include $(srctree)/arch/$(SRCARCH)/Makefile
export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT RUSTC_VERSION_TEXT
export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT RUSTC_VERSION_TEXT PAHOLE_VERSION
config: outputmakefile scripts_basic FORCE
$(Q)$(MAKE) $(build)=scripts/kconfig $@
@ -1921,12 +1922,18 @@ clean: private rm-files := Module.symvers modules.nsdeps compile_commands.json
PHONY += prepare
# now expand this into a simple variable to reduce the cost of shell evaluations
prepare: CC_VERSION_TEXT := $(CC_VERSION_TEXT)
prepare: PAHOLE_VERSION := $(PAHOLE_VERSION)
prepare:
@if [ "$(CC_VERSION_TEXT)" != "$(CONFIG_CC_VERSION_TEXT)" ]; then \
echo >&2 "warning: the compiler differs from the one used to build the kernel"; \
echo >&2 " The kernel was built by: $(CONFIG_CC_VERSION_TEXT)"; \
echo >&2 " You are using: $(CC_VERSION_TEXT)"; \
fi
@if [ "$(PAHOLE_VERSION)" != "$(CONFIG_PAHOLE_VERSION)" ]; then \
echo >&2 "warning: pahole version differs from the one used to build the kernel"; \
echo >&2 " The kernel was built with: $(CONFIG_PAHOLE_VERSION)"; \
echo >&2 " You are using: $(PAHOLE_VERSION)"; \
fi
PHONY += help
help: