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

Julien Thierry
2018-08-14T08:34:01Z

On 14/08/18 03:03, Steven Rostedt wrote:
> On Mon, 13 Aug 2018 11:54:06 +0100
> Julien Thierry <julien.thierry@arm.com> wrote:
>
>>> --- a/arch/arm64/Makefile
>>> +++ b/arch/arm64/Makefile
>>> @@ -78,6 +78,15 @@ ifeq ($(CONFIG_ARM64_MODULE_PLTS),y)
>>> KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/module.lds
>>> endif
>>>
>>> +ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>>> + CC_FLAGS_FTRACE := -fpatchable-function-entry=2
>>> + KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
>>> + ifeq ($(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