linux-kernel - Re: [PATCH] riscv: Only allow LTO with CMODEL

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Message-ID: <20250808215303.GA3695089@ax162>
Date: Fri, 8 Aug 2025 14:53:03 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>
Cc: Conor Dooley <conor@...nel.org>, linux-riscv@...ts.infradead.org,
	llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] riscv: Only allow LTO with CMODEL_MEDANY

Ping? This is still getting hit.

On Thu, Jul 10, 2025 at 01:25:26PM -0700, Nathan Chancellor wrote:
> When building with CONFIG_CMODEL_MEDLOW and CONFIG_LTO_CLANG, there is a
> series of errors due to some files being unconditionally compiled with
> '-mcmodel=medany', mismatching with the rest of the kernel built with
> '-mcmodel=medlow':
> 
>   ld.lld: error: Function Import: link error: linking module flags 'Code Model': IDs have conflicting values: 'i32 3' from vmlinux.a(init.o at 899908), and 'i32 1' from vmlinux.a(net-traces.o at 1014628)
> 
> Only allow LTO to be performed when CONFIG_CMODEL_MEDANY is enabled to
> ensure there will be no code model mismatch errors. An alternative
> solution would be disabling LTO for the files with a different code
> model than the main kernel like some specialized areas of the kernel do
> but doing that for individual files is not as sustainable than
> forbidding the combination altogether.
> 
> Cc: stable@...r.kernel.org
> Fixes: 021d23428bdb ("RISC-V: build: Allow LTO to be selected")
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202506290255.KBVM83vZ-lkp@intel.com/
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  arch/riscv/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 36061f4732b7..4eee737a050f 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -68,7 +68,7 @@ config RISCV
>  	select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
>  	select ARCH_SUPPORTS_HUGETLBFS if MMU
>  	# LLD >= 14: https://github.com/llvm/llvm-project/issues/50505
> -	select ARCH_SUPPORTS_LTO_CLANG if LLD_VERSION >= 140000
> +	select ARCH_SUPPORTS_LTO_CLANG if LLD_VERSION >= 140000 && CMODEL_MEDANY
>  	select ARCH_SUPPORTS_LTO_CLANG_THIN if LLD_VERSION >= 140000
>  	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS if 64BIT && MMU
>  	select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU
> 
> ---
> base-commit: fda589c286040d9ba2d72a0eaf0a13945fc48026
> change-id: 20250710-riscv-restrict-lto-to-medany-f1b7dd5c9bba
> 
> Best regards,
> --  
> Nathan Chancellor <nathan@...nel.org>
>