Re: [Buildroot] [PATCH] package/mesa3d: fix compilation with host-llvm enabled

From: Thomas Petazzoni via buildroot <buildroot@buildroot.org>
To: Thomas Devoogdt <thomas@devoogdt.com>
Cc: buildroot@buildroot.org, Bernd Kuhls <bernd@kuhls.net>,
	Romain Naour <romain.naour@gmail.com>,
	Thomas Devoogdt <thomas.devoogdt@barco.com>
Subject: Re: [Buildroot] [PATCH] package/mesa3d: fix compilation with host-llvm enabled
Date: Fri, 26 Dec 2025 10:14:45 +0100	[thread overview]
Message-ID: <20251226101445.2b29f439@windsurf> (raw)
In-Reply-To: <20251218125030.154446-1-thomas@devoogdt.com>

Hello Thomas,

Thanks for your patch!

On Thu, 18 Dec 2025 13:50:29 +0100
Thomas Devoogdt <thomas@devoogdt.com> wrote:

> From: Thomas Devoogdt <thomas.devoogdt@barco.com>
> 
> Meson's custom LLVM parser uses llvm-config with a default search path of
> /usr/bin, causing it to detect the host system's llvm-config (version 18.1.3)
> instead of the buildroot-compiled one. This forces all LLVM-related packages to
> match version 18.1.3, but since the host system lacks llvmspirvlib, the build
> fails. This patch forces Meson to use the buildroot-compiled llvm-config.
> 
> Fixes:
> 
>   llvm-config found: YES (/usr/bin/llvm-config-18) 18.1.3
>   Run-time dependency LLVM (modules: bitwriter, core, coverage, engine, executionengine, instcombine, irreader, libdriver, linker, lto, mcdisassembler, mcjit, native, option, scalaropts, target, transformutils, all-targets, coroutines, frontenddriver, frontendhlsl, lto, windowsdriver) found: YES 18.1.3
>   Dependency LLVMSPIRVLib found: NO. Found 15.0.0.0 but need: '>= 18.1' ; matched: '>= 15.0.0.0', '< 18.2'
>   Run-time dependency llvmspirvlib found: NO (tried cmake)
> 
>   output/build/host-mesa3d-25.0.6/meson.build:1882:21: ERROR: Dependency lookup for LLVMSPIRVLib with method 'pkgconfig' failed: Invalid version, need 'LLVMSPIRVLib' ['>= 18.1'] found '15.0.0.0'.
> 
>   A full log can be found at /home/thomas/buildroot/output/build/host-mesa3d-25.0.6/buildroot-build/meson-logs/meson-log.txt
>   make[1]: *** [package/pkg-generic.mk:263: /home/thomas/buildroot/output/build/host-mesa3d-25.0.6/.stamp_configured] Error 1
>   make: *** [Makefile:83: _all] Error 2
> 
> Signed-off-by: Thomas Devoogdt <thomas.devoogdt@barco.com>
> ---
>  package/mesa3d/mesa3d.mk | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/package/mesa3d/mesa3d.mk b/package/mesa3d/mesa3d.mk
> index 6fcbf96c803..36bc3d6542a 100644
> --- a/package/mesa3d/mesa3d.mk
> +++ b/package/mesa3d/mesa3d.mk
> @@ -40,6 +40,7 @@ ifeq ($(BR2_PACKAGE_MESA3D_LLVM),y)
>  MESA3D_DEPENDENCIES += host-llvm llvm
>  MESA3D_MESON_EXTRA_BINARIES += llvm-config='$(STAGING_DIR)/usr/bin/llvm-config'
>  MESA3D_CONF_OPTS += -Dllvm=enabled
> +HOST_MESA3D_CONF_ENV += LLVM_CONFIG="$(HOST_DIR)/bin/llvm-config"

This looks odd to me, as it isn't tied to us passing -Dllvm=<something>
to HOST_MESA3D_CONF_OPTS.

If LLVM support in host-mesa3d is needed, then we should pass
-Dllvm=enabled and this LLVM_CONFIG variable. If LLVM support in
host-mesa3d is not needed (which I would recommend to try first), then
we should pass -Dllvm=disabled, and passing LLVM_CONFIG should not be
needed.

The other thing that bothers me is that to do the same thing ("i.e
passing the path to llvm-config"), we're using here two different
mechanisms: MESA3D_MESON_EXTRA_BINARIES for the target mesa3d package,
and LLVM_CONFIG for the host mesa3d package. This is not consistent and
therefore isn't great.

Could you try to improve those two aspects?

Thanks a lot!

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