[PATCH v4 07/29] tracing: add support for objtool mcount

[Sami Tolvanen]

This change adds build support for using objtool to generate
__mcount_loc sections.

Signed-off-by: Sami Tolvanen <samitolvanen at google.com>
---
 Makefile             | 12 ++++++++++--
 kernel/trace/Kconfig | 13 +++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 77e4f0a9495e..9717005e41c4 100644
--- a/Makefile
+++ b/Makefile
@@ -850,6 +850,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
     endif
   endif
 endif
+ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+  CC_FLAGS_USING	+= -DCC_USING_NOP_MCOUNT
+endif
 ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
   ifdef CONFIG_HAVE_C_RECORDMCOUNT
     BUILD_C_RECORDMCOUNT := y
@@ -1209,11 +1212,16 @@ 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 CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+	@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 927ad004888a..89263210ab26 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -51,6 +51,11 @@ config HAVE_NOP_MCOUNT
 	help
 	  Arch supports the gcc options -pg with -mrecord-mcount and -nop-mcount
 
+config HAVE_OBJTOOL_MCOUNT
+	bool
+	help
+	  Arch supports objtool --mcount
+
 config HAVE_C_RECORDMCOUNT
 	bool
 	help
@@ -605,10 +610,18 @@ config FTRACE_MCOUNT_USE_CC
 	depends on !FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
 	depends on FTRACE_MCOUNT_RECORD
 
+config FTRACE_MCOUNT_USE_OBJTOOL
+	def_bool y
+	depends on HAVE_OBJTOOL_MCOUNT
+	depends on !FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
+	depends on !FTRACE_MCOUNT_USE_CC
+	depends on FTRACE_MCOUNT_RECORD
+
 config FTRACE_MCOUNT_USE_RECORDMCOUNT
 	def_bool y
 	depends on !FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
 	depends on !FTRACE_MCOUNT_USE_CC
+	depends on !FTRACE_MCOUNT_USE_OBJTOOL
 	depends on FTRACE_MCOUNT_RECORD
 
 config TRACING_MAP
-- 
2.28.0.709.gb0816b6eb0-goog