With current gcc, compiling with both -pg and -fomit-frame-pointer is
not allowed. However, -pg can be used to build without actually
specying -fno-omit-frame-pointer, upon which the defaut behaviour for
the target will be used.
On ARM, it is not possible to build a Thumb-2 kernel with
-fno-omit-frame-pointer (FRAME_POINTERS depends on !THUMB2_KERNEL). In
order to support ftrace for Thumb-2, we need to be able to allow a
combination of FUNCTION_TRACER and !FRAME_POINTER. We do this by
omitting -fomit-frame-pointer if ftrace is enabled.
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Rabin Vincent <rabin@rab.in>
---
v2: Better comment.
Makefile | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/Makefile b/Makefile
index 08ff02d..61404e0 100644
--- a/Makefile
+++ b/Makefile
@@ -546,8 +546,15 @@ endif
ifdef CONFIG_FRAME_POINTER
KBUILD_CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
else
+# Some targets (ARM with Thumb2, for example), can't be built with frame
+# pointers. For those, we don't have FUNCTION_TRACER automatically
+# select FRAME_POINTER. However, FUNCTION_TRACER adds -pg, and this is
+# incompatible with -fomit-frame-pointer with current GCC, so we don't use
+# -fomit-frame-pointer with FUNCTION_TRACER.
+ifndef CONFIG_FUNCTION_TRACER
KBUILD_CFLAGS += -fomit-frame-pointer
endif
+endif
ifdef CONFIG_DEBUG_INFO
KBUILD_CFLAGS += -g
--
1.7.0
--
