Re: [Buildroot] [PATCH v4 1/1] package/linux-tools: use PKG_CONFIG_LIBDIR in perf make flags

From: Thomas Petazzoni via buildroot <buildroot@buildroot.org>
To: Vasileios Amoiridis <vassilisamir@gmail.com>
Cc: buildroot@buildroot.org
Subject: Re: [Buildroot] [PATCH v4 1/1] package/linux-tools: use PKG_CONFIG_LIBDIR in perf make flags
Date: Sat, 19 Apr 2025 23:40:47 +0200	[thread overview]
Message-ID: <20250419234047.2a5f229f@windsurf> (raw)
In-Reply-To: <20250403224419.26193-1-vassilisamir@gmail.com>

Hello Vasileios,

On Fri,  4 Apr 2025 00:44:17 +0200
Vasileios Amoiridis <vassilisamir@gmail.com> wrote:

> After commit 440cf77625e300e683ca0edc39fbc4b6f3175feb ("perf:
> build: Setup PKG_CONFIG_LIBDIR for cross compilation") in the
> Linux Kernel it is needed to add PKG_CONFIG_LIBDIR in the
> make flags to avoid warnings from the Kernel, such as:
> 
>         Makefile.perf:207: Missing PKG_CONFIG_LIBDIR,
>         PKG_CONFIG_PATH and PKG_CONFIG_SYSROOT_DIR for
>         cross compilation,
>         Makefile.perf:208: set PKG_CONFIG_LIBDIR for using
>         Multiarch libs.
> 
> Signed-off-by: Vasileios Amoiridis <vassilisamir@gmail.com>

Thanks for the patch!

> diff --git a/package/linux-tools/linux-tool-perf.mk.in b/package/linux-tools/linux-tool-perf.mk.in
> index d67318571a..1526652ce4 100644
> --- a/package/linux-tools/linux-tool-perf.mk.in
> +++ b/package/linux-tools/linux-tool-perf.mk.in
> @@ -20,6 +20,7 @@ endif
>  
>  PERF_MAKE_FLAGS = \
>  	$(LINUX_MAKE_FLAGS) \
> +	PKG_CONFIG_LIBDIR=$(HOST_DIR)/lib/pkgconfig:$(HOST_DIR)/share/pkgconfig \

However, this value is incorrect I believe.

Indeed, linux-tool-perf.mk.in is cross-compiling perf for the target,
so pkg-config should look for cross-compiled libraries... and here
you're pointing to natively compiled libraries installed in
$(HOST_DIR), so this is not correct.

I'm not sure what the correct fix is, as PKG_CONFIG_LIBDIR is passed
internally in our pkg-config wrapper, it's really just the kernel
Makefile being over-zealous here. Maybe we could play with the kernel
accepting a $(CROSS_COMPILE)pkg-config, and have such a script in a
private directory, added in the PATH when building perf? Another option
is to define PKG_CONFIG_LIBDIR, replicating what our pkg-config uses as
a value.

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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