Re: [PATCH] Why does libtracevent pkg-config detection wipe PKG_CONFIG_PATH?

["Mateusz Kowalczyk" <fuuzetsu@fuuzetsu.co.uk>]

On Tue, 4 Jun 2024, at 10:26 PM, Leo Yan wrote:
> Hi Mateusz,
>
> On 5/27/24 01:56, Mateusz Kowalczyk wrote:
>> Hi,
>> 
>> To build recent perf, I'm having to apply the below patch.
>> 
>> ```diff
>> ---
>> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
>> index 7f1e016a9253..b70fef12a977 100644
>> --- a/tools/perf/Makefile.config
>> +++ b/tools/perf/Makefile.config
>> @@ -1181,7 +1181,7 @@ ifneq ($(NO_LIBTRACEEVENT),1)
>>       CFLAGS += -DHAVE_LIBTRACEEVENT $(LIBTRACEEVENT_CFLAGS)
>>       LDFLAGS += $(LIBTRACEEVENT_LDFLAGS)
>>       EXTLIBS += ${TRACEEVENTLIBS}
>> -    LIBTRACEEVENT_VERSION := $(shell PKG_CONFIG_PATH=$(LIBTRACEEVENT_DIR) $(PKG_CONFIG) --modversion libtraceevent)
>> +    LIBTRACEEVENT_VERSION := $(shell $(PKG_CONFIG) --modversion libtraceevent)
>>       LIBTRACEEVENT_VERSION_1 := $(word 1, $(subst ., ,$(LIBTRACEEVENT_VERSION)))
>>       LIBTRACEEVENT_VERSION_2 := $(word 2, $(subst ., ,$(LIBTRACEEVENT_VERSION)))
>>       LIBTRACEEVENT_VERSION_3 := $(word 3, $(subst ., ,$(LIBTRACEEVENT_VERSION)))
>> ```
>> 
>> I don't understand why `PKG_CONFIG_PATH` is overwritten this way. `grep`ing for PKG_CONFIG_PATH reveals that this isn't done anywhere else in the kernel tree. All other uses of `$(PKG_CONFIG)` in the file simply invoke the tool.
>> 
>> Of course, I do actually have `libtraceevent.pc` available, it's just that `LIBTRACEVENT_DIR` is empty which stops it from finding it.
>
> When I was fixing the cross compilation issue for perf, I also 
> encountered the similar issue with you. I have sent a patch series to 
> resolve the compilation issue.
>
> It will be appreciated if you could check if the patch [1] can fix your 
> reported issue or not.

Hi Leo,

I applied the linked patch on top of latest kernel tree checkout and I can confirm that it fixes the issue for me, thank you!

> Also thanks for James' reminding.
>
> Thanks,
> Leo
>
> [1] 
> https://lore.kernel.org/linux-perf-users/20240604093223.1934236-3-leo.yan@arm.com/T/#u



--
Mateusz K.