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Subject[PATCH v2 07/28] kbuild: add support for objtool mcount
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This change adds build support for using objtool to generate
__mcount_loc sections.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
Makefile | 38 ++++++++++++++++++++++++++++++--------
kernel/trace/Kconfig | 5 +++++
scripts/Makefile.build | 9 +++++----
3 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index ff5e0731d26d..a9dae26c93b5 100644
--- a/Makefile
+++ b/Makefile
@@ -859,17 +859,34 @@ ifdef CONFIG_HAVE_FENTRY
ifeq ($(call cc-option-yn, -mfentry),y)
CC_FLAGS_FTRACE += -mfentry
CC_FLAGS_USING += -DCC_USING_FENTRY
+ export CC_USING_FENTRY := 1
endif
endif
export CC_FLAGS_FTRACE
-KBUILD_CFLAGS += $(CC_FLAGS_FTRACE) $(CC_FLAGS_USING)
-KBUILD_AFLAGS += $(CC_FLAGS_USING)
ifdef CONFIG_DYNAMIC_FTRACE
- ifdef CONFIG_HAVE_C_RECORDMCOUNT
- BUILD_C_RECORDMCOUNT := y
- export BUILD_C_RECORDMCOUNT
- endif
+ ifndef CC_USING_RECORD_MCOUNT
+ ifndef CC_USING_PATCHABLE_FUNCTION_ENTRY
+ # use objtool or recordmcount to generate mcount tables
+ ifdef CONFIG_HAVE_OBJTOOL_MCOUNT
+ ifdef CC_USING_FENTRY
+ USE_OBJTOOL_MCOUNT := y
+ CC_FLAGS_USING += -DCC_USING_NOP_MCOUNT
+ export USE_OBJTOOL_MCOUNT
+ endif
+ endif
+ ifndef USE_OBJTOOL_MCOUNT
+ USE_RECORDMCOUNT := y
+ export USE_RECORDMCOUNT
+ ifdef CONFIG_HAVE_C_RECORDMCOUNT
+ BUILD_C_RECORDMCOUNT := y
+ export BUILD_C_RECORDMCOUNT
+ endif
+ endif
+ endif
+ endif
endif
+KBUILD_CFLAGS += $(CC_FLAGS_FTRACE) $(CC_FLAGS_USING)
+KBUILD_AFLAGS += $(CC_FLAGS_USING)
endif

# We trigger additional mismatches with less inlining
@@ -1218,11 +1235,16 @@ uapi-asm-generic:
PHONY += prepare-objtool prepare-resolve_btfids
prepare-objtool: $(objtool_target)
ifeq ($(SKIP_STACK_VALIDATION),1)
+objtool-lib-prompt := "please install libelf-dev, libelf-devel or elfutils-libelf-devel"
+ifdef USE_OBJTOOL_MCOUNT
+ @echo "error: Cannot generate __mcount_loc for CONFIG_DYNAMIC_FTRACE=y, $(objtool-lib-prompt)" >&2
+ @false
+endif
ifdef CONFIG_UNWINDER_ORC
- @echo "error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
+ @echo "error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, $(objtool-lib-prompt)" >&2
@false
else
- @echo "warning: Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
+ @echo "warning: Cannot use CONFIG_STACK_VALIDATION=y, $(objtool-lib-prompt)" >&2
endif
endif

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index a4020c0b4508..b510af5b216c 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -56,6 +56,11 @@ config HAVE_C_RECORDMCOUNT
help
C version of recordmcount available?

+config HAVE_OBJTOOL_MCOUNT
+ bool
+ help
+ Arch supports objtool --mcount
+
config TRACER_MAX_TRACE
bool

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a467b9323442..6ecf30c70ced 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -178,8 +178,7 @@ cmd_modversions_c = \
fi
endif

-ifdef CONFIG_FTRACE_MCOUNT_RECORD
-ifndef CC_USING_RECORD_MCOUNT
+ifdef USE_RECORDMCOUNT
# compiler will not generate __mcount_loc use recordmcount or recordmcount.pl
ifdef BUILD_C_RECORDMCOUNT
ifeq ("$(origin RECORDMCOUNT_WARN)", "command line")
@@ -206,8 +205,7 @@ recordmcount_source := $(srctree)/scripts/recordmcount.pl
endif # BUILD_C_RECORDMCOUNT
cmd_record_mcount = $(if $(findstring $(strip $(CC_FLAGS_FTRACE)),$(_c_flags)), \
$(sub_cmd_record_mcount))
-endif # CC_USING_RECORD_MCOUNT
-endif # CONFIG_FTRACE_MCOUNT_RECORD
+endif # USE_RECORDMCOUNT

ifdef CONFIG_STACK_VALIDATION
ifneq ($(SKIP_STACK_VALIDATION),1)
@@ -230,6 +228,9 @@ endif
ifdef CONFIG_X86_SMAP
objtool_args += --uaccess
endif
+ifdef USE_OBJTOOL_MCOUNT
+ objtool_args += --mcount
+endif

# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
--
2.28.0.402.g5ffc5be6b7-goog
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