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Subject[PATCH 1/2] ftrace: Speed up recordmcount
From: Wu Zhangjin <wuzhangjin@gmail.com>

cmd_record_mcount is used to locate the _mcount symbols in the object
files, only the files compiled with -pg has the _mcount symbol, so, it
is only needed for such files, but the current cmd_record_mcount is used
for all of the object files, so, we need to fix it and speed it up.

Since -pg may be removed by the method used in kernel/trace/Makefile:

ORIG_CFLAGS := $(KBUILD_CFLAGS)
KBUILD_CFLAGS = $(subst -pg,,$(ORIG_CFLAGS))

Or may be removed by the method used in arch/x86/kernel/Makefile:

CFLAGS_REMOVE_file.o = -pg

So, we must check the last variable stores the compiling flags, that is
c_flags(Please refer to cmd_cc_o_c and rule_cc_o_c defined in
scripts/Makefile.build) and since the CFLAGS_REMOVE_file.o is already
filtered in _c_flags(Please refer to scripts/Makefile.lib) and _c_flags
has less symbols, therefore, we only need to check _c_flags.

---------------
Changes from v1:

o Don't touch Makefile for CONFIG_FTRACE_MCOUNT_RECORD is enough
o Use _c_flags intead of KBUILD_CFLAGS to cover CONFIG_REMOVE_file.o = -pg
(feedback from Steven Rostedt <rostedt@goodmis.org>)

Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
LKML-Reference: <3dc8cddf022eb7024f9f2cf857529a15bee8999a.1288196498.git.wuzhangjin@gmail.com>

[ changed if [ .. == .. ] to if [ .. = .. ] to handle dash environments ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
scripts/Makefile.build | 13 +++++++++----
1 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 5ad25e1..4eb99ab 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -214,17 +214,22 @@ ifdef BUILD_C_RECORDMCOUNT
# The empty.o file is created in the make process in order to determine
# the target endianness and word size. It is made before all other C
# files, including recordmcount.
-cmd_record_mcount = if [ $(@) != "scripts/mod/empty.o" ]; then \
- $(objtree)/scripts/recordmcount "$(@)"; \
- fi;
+sub_cmd_record_mcount = \
+ if [ $(@) != "scripts/mod/empty.o" ]; then \
+ $(objtree)/scripts/recordmcount "$(@)"; \
+ fi;
else
-cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
+sub_cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
"$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
"$(if $(CONFIG_64BIT),64,32)" \
"$(OBJDUMP)" "$(OBJCOPY)" "$(CC) $(KBUILD_CFLAGS)" \
"$(LD)" "$(NM)" "$(RM)" "$(MV)" \
"$(if $(part-of-module),1,0)" "$(@)";
endif
+cmd_record_mcount = \
+ if [ "$(findstring -pg,$(_c_flags))" = "-pg" ]; then \
+ $(sub_cmd_record_mcount) \
+ fi;
endif

define rule_cc_o_c
--
1.7.1



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