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Subject[PATCH 3/5] kernel hacking: new config NO_AUTO_INLINE to disable compiler atuo-inline optimizations
Date
From: Changbin Du <changbin.du@intel.com>

This patch add a new kernel hacking option NO_AUTO_INLINE. Selecting
this option will make compiler not auto-inline kernel functions. By
enabling this option, all the kernel functions (including static ones)
will not be optimized out except those marked as inline or always_inline.
This is useful when you are using ftrace to understand the control flow
of kernel code or tracing some static functions.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
Makefile | 6 ++++++
lib/Kconfig.debug | 13 +++++++++++++
2 files changed, 19 insertions(+)

diff --git a/Makefile b/Makefile
index 619a85a..eb694f6 100644
--- a/Makefile
+++ b/Makefile
@@ -775,6 +775,12 @@ KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
$(call cc-option,-fno-var-tracking)
endif

+ifdef CONFIG_NO_AUTO_INLINE
+KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions) \
+ $(call cc-option, -fno-inline-small-functions) \
+ $(call cc-option, -fno-inline-functions-called-once)
+endif
+
ifdef CONFIG_FUNCTION_TRACER
ifndef CC_FLAGS_FTRACE
CC_FLAGS_FTRACE := -pg
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c40c7b7..90f35ad 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -198,6 +198,19 @@ config GDB_SCRIPTS
instance. See Documentation/dev-tools/gdb-kernel-debugging.rst
for further details.

+config NO_AUTO_INLINE
+ bool "Disable compiler atuo-inline optimizations"
+ default n
+ help
+ This will make compiler not auto-inline kernel functions for
+ optimization. By enabling this option, all the kernel functions
+ (including static ones) will not be optimized out except those
+ marked as inline or always_inline. This is useful when you are
+ using ftrace to understand the control flow of kernel code or
+ tracing some static functions.
+
+ Use only if you want to debug the kernel.
+
config ENABLE_WARN_DEPRECATED
bool "Enable __deprecated logic"
default y
--
2.7.4
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