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kbuild: move GCOV flags to scripts/Makefile.gcov

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* split the CFLAGS_GCOV block out of the top-level Makefile into
   scripts/Makefile.gcov
 * include it via include-$(CONFIG_GCOV_KERNEL) like neighbour
   KASAN/KCOV/UBSAN makefiles do
 * keep the include before scripts/Makefile.gcc-plugins: the try-run
   must not get -fplugin= options, plugins do not exist on clean builds

CFLAGS_GCOV is no longer defined when CONFIG_GCOV_KERNEL is off:
 * its user in scripts/Makefile.lib is guarded by the CONFIG_GCOV_KERNEL
 * in i915/xe header an empty value is harmless

The try-run compiler invocations also stop running on builds without
GCOV.

Link: https://lore.kernel.org/20261001-b4-prep-gcov-v1-2-794792e06f24@virtuozzo.com
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nsc@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Mikhail Zaslonko <zaslonko@linux.ibm.com>
This commit is contained in:
Konstantin Khorenko 2026-10-01 18:57:12 +02:00 committed by Andrew Morton
parent 4719c92641
commit f541906e89
3 changed files with 23 additions and 21 deletions
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1
MAINTAINERS
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@ -10899,6 +10899,7 @@ M: Peter Oberparleiter <oberpar@linux.ibm.com>
S: Maintained
F: Documentation/dev-tools/gcov.rst
F: kernel/gcov/
F: scripts/Makefile.gcov
GDB KERNEL DEBUGGING HELPER SCRIPTS
M: Jan Kiszka <jan.kiszka@siemens.com>

22
Makefile
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@ -1176,27 +1176,6 @@ endif
# Ensure compilers do not transform certain loops into calls to wcslen()
KBUILD_CFLAGS += -fno-builtin-wcslen
CFLAGS_GCOV := -fprofile-arcs -ftest-coverage
ifdef CONFIG_CC_IS_GCC
CFLAGS_GCOV += -fno-tree-loop-im
# Use atomic counter updates to avoid concurrent-access crashes in GCOV.
# Only enable if -fprofile-update=prefer-atomic does not introduce new
# undefined symbols (e.g. libatomic calls that the kernel cannot link).
CFLAGS_GCOV += $(call try-run,\
echo 'long long x; void f(void){x++;}' | \
$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -w $(CFLAGS_GCOV) \
-x c - -c -o "$$TMP.base" && \
echo 'long long x; void f(void){x++;}' | \
$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -w $(CFLAGS_GCOV) \
-fprofile-update=prefer-atomic \
-x c - -c -o "$$TMP" && \
$(NM) "$$TMP.base" | grep ' U ' > "$$TMP.ubase" || true ; \
$(NM) "$$TMP" | grep ' U ' > "$$TMP.utest" || true ; \
cmp -s "$$TMP.ubase" "$$TMP.utest",\
-fprofile-update=prefer-atomic)
endif
export CFLAGS_GCOV
# change __FILE__ to the relative path to the source directory
ifdef building_out_of_srctree
KBUILD_CPPFLAGS += -fmacro-prefix-map=$(srcroot)/=
@ -1214,6 +1193,7 @@ include-$(CONFIG_KCSAN) += scripts/Makefile.kcsan
include-$(CONFIG_KMSAN) += scripts/Makefile.kmsan
include-$(CONFIG_UBSAN) += scripts/Makefile.ubsan
include-$(CONFIG_KCOV) += scripts/Makefile.kcov
include-$(CONFIG_GCOV_KERNEL) += scripts/Makefile.gcov
include-$(CONFIG_RANDSTRUCT) += scripts/Makefile.randstruct
include-$(CONFIG_KSTACK_ERASE) += scripts/Makefile.kstack_erase
include-$(CONFIG_AUTOFDO_CLANG) += scripts/Makefile.autofdo

21
scripts/Makefile.gcov Normal file
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@ -0,0 +1,21 @@
# SPDX-License-Identifier: GPL-2.0-only
CFLAGS_GCOV := -fprofile-arcs -ftest-coverage
ifdef CONFIG_CC_IS_GCC
CFLAGS_GCOV += -fno-tree-loop-im
# Use atomic counter updates to avoid concurrent-access crashes in GCOV.
# Only enable if -fprofile-update=prefer-atomic does not introduce new
# undefined symbols (e.g. libatomic calls that the kernel cannot link).
CFLAGS_GCOV += $(call try-run,\
echo 'long long x; void f(void){x++;}' | \
$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -w $(CFLAGS_GCOV) \
-x c - -c -o "$$TMP.base" && \
echo 'long long x; void f(void){x++;}' | \
$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -w $(CFLAGS_GCOV) \
-fprofile-update=prefer-atomic \
-x c - -c -o "$$TMP" && \
$(NM) "$$TMP.base" | grep ' U ' > "$$TMP.ubase" || true ; \
$(NM) "$$TMP" | grep ' U ' > "$$TMP.utest" || true ; \
cmp -s "$$TMP.ubase" "$$TMP.utest",\
-fprofile-update=prefer-atomic)
endif
export CFLAGS_GCOV