As a Kernel developer, I make heavy use of "make targz-pkg" in order
to locally compile and remotely install my development Kernels. The
nice feature I rely on is that after a normal "make", "make targz-pkg"
only generates the tarball without having to recompile everything.
That was true until commit f28bc3c32c05 ("tracing: Handle
CC_FLAGS_FTRACE more accurately"). After it, running "make targz-pkg"
after "make" will recompile the whole Kernel tree, making my
development workflow much slower.
The Kernel is choosing to recompile everything because it claims the
command line has changed. A diff of the .cmd files show a repeated
-mfentry in one of the files. That is because "make targz-pkg" calls
"make modules_install" and the environment is already populated with
the exported variables, CC_FLAGS_FTRACE being one of them. Then,
-mfentry gets duplicated because it is not protected behind an ifndef
block, like -pg.
To complicate the problem a little bit more, architectures can define
their own version CC_FLAGS_FTRACE, so our code not only has to
consider recursive Makefiles, but also architecture overrides.
So in this patch we move CC_FLAGFS_FTRACE up and unconditionally
define it to -pg. Then we let the architecture Makefiles possibly
override it, and finally append the extra options later. This ensures
the variable is always fully redefined at each invocation so recursive
Makefiles don't keep appending, and hopefully it maintains the
intended behavior on how architectures can override the defaults..
Thanks Steven Rostedt and Vasily Gorbik for the help on this
regression.
Fixes: commit f28bc3c32c05 ("tracing: Handle CC_FLAGS_FTRACE more
accurately")
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: linux-kbuild@xxxxxxxxxxxxxxx
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
---
Makefile | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/Makefile b/Makefile
index 4d5c883a98e5..a5ef6818157a 100644
--- a/Makefile
+++ b/Makefile
@@ -616,6 +616,11 @@ CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \
$(call cc-disable-warning,maybe-uninitialized,)
export CFLAGS_GCOV
+# The arch Makefiles can override CC_FLAGS_FTRACE. We may also append it later.
+ifdef CONFIG_FUNCTION_TRACER
+ CC_FLAGS_FTRACE := -pg
+endif
+
# The arch Makefile can set ARCH_{CPP,A,C}FLAGS to override the default
# values of the respective KBUILD_* variables
ARCH_CPPFLAGS :=
@@ -755,9 +760,6 @@ KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
endif
ifdef CONFIG_FUNCTION_TRACER
-ifndef CC_FLAGS_FTRACE
-CC_FLAGS_FTRACE := -pg
-endif
ifdef CONFIG_FTRACE_MCOUNT_RECORD
# gcc 5 supports generating the mcount tables directly
ifeq ($(call cc-option-yn,-mrecord-mcount),y)
--
2.17.1
