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Subject[PATCH 3/4] trace: add -mcount-nop option support
-mcount-nop gcc option generates the calls to the profiling functions
as nops which allows to avoid patching mcount jump with NOP instructions
initially.

-mcount-nop gcc option will be activated if platform selects
HAVE_NOP_MCOUNT and gcc actually supports it.
In addition to that CC_USING_NOP_MCOUNT is defined and could be used by
architectures to adapt ftrace patching behavior.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---
Makefile | 6 ++++++
kernel/trace/Kconfig | 5 +++++
kernel/trace/ftrace.c | 2 ++
3 files changed, 13 insertions(+)

diff --git a/Makefile b/Makefile
index 621ebdbfbf89..281f4ededf3a 100644
--- a/Makefile
+++ b/Makefile
@@ -749,6 +749,12 @@ ifdef CONFIG_FTRACE_MCOUNT_RECORD
CC_FLAGS_FTRACE += -mrecord-mcount
export CC_USING_RECORD_MCOUNT := 1
endif
+ ifdef CONFIG_HAVE_NOP_MCOUNT
+ ifeq ($(call cc-option-yn, -mnop-mcount),y)
+ CC_FLAGS_FTRACE += -mnop-mcount
+ CC_FLAGS_USING += -DCC_USING_NOP_MCOUNT
+ endif
+ endif
endif
ifdef CONFIG_HAVE_FENTRY
ifeq ($(call cc-option-yn, -mfentry),y)
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index dcc0166d1997..855109214e3d 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -47,6 +47,11 @@ config HAVE_FENTRY
help
Arch supports the gcc options -pg with -mfentry

+config HAVE_NOP_MCOUNT
+ bool
+ help
+ Arch supports the gcc options -pg with -mrecord-mcount and -nop-mcount
+
config HAVE_C_RECORDMCOUNT
bool
help
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index caf9cbf35816..310dfcb20d5b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2981,12 +2981,14 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
p = &pg->records[i];
p->flags = rec_flags;

+#ifndef CC_USING_NOP_MCOUNT
/*
* Do the initial record conversion from mcount jump
* to the NOP instructions.
*/
if (!ftrace_code_disable(mod, p))
break;
+#endif

update_cnt++;
}
--
2.18.0.13.gd42ae10
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