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

[Leo Yan <niayan01@foss.arm.com>]

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.

Also thanks for James' reminding.

Thanks,
Leo

[1] 
https://lore.kernel.org/linux-perf-users/20240604093223.1934236-3-leo.yan@arm.com/T/#u