Re: [PATCH 1/3] arm64: implement ftrace with regs

From: Julien Thierry
Date: Tue Aug 14 2018 - 09:27:33 EST

On 14/08/18 03:03, Steven Rostedt wrote:
On Mon, 13 Aug 2018 11:54:06 +0100
Julien Thierry <julien.thierry@xxxxxxx> wrote:

--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -78,6 +78,15 @@ ifeq ($(CONFIG_ARM64_MODULE_PLTS),y)
KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/
+ CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+ ifeq ($(call cc-option,-fpatchable-function-entry=2),)
+ $(warning Cannot use CONFIG_DYNAMIC_FTRACE_WITH_REGS: \
+ -fpatchable-function-entry not supported by compiler)

Shouldn't this be an error? The option -fpatchable-function-entry has
been added to the CC_FLAGS_FTRACE, so any call to the compiler is gonna
break anyway. Or am I missing something?

I'm guessing this adds a more informative message on that error. One
will know why -fpatchable-function-entry was added to the CFLAGS. I'm
for more informative error messages being a victim of poor error
messages causing me to dig deep into the guts of the build
infrastructure to figure out simple issues.

Yes, I agree it is better to have this message. My point was that we could have "$error" instead of "$warning" to stop the compilation right away since we know everything is gonna break (and on parallel builds this warning is gonna be drowned in compiler errors).

Julien Thierry