Re: [PATCH v2 2/7] MIPS: Add toolchain feature dependency for microMIPS smartMIPS

From: Nathan Chancellor <nathan@kernel.org>
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
	llvm@lists.linux.dev, Borislav Petkov <bp@alien8.de>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>
Subject: Re: [PATCH v2 2/7] MIPS: Add toolchain feature dependency for microMIPS smartMIPS
Date: Mon, 24 Apr 2023 10:03:03 -0700	[thread overview]
Message-ID: <20230424170303.GA1255815@dev-arch.thelio-3990X> (raw)
In-Reply-To: <77F56166-265A-4653-ADF4-B0057604A539@flygoat.com>

On Thu, Apr 20, 2023 at 08:41:07PM +0100, Jiaxun Yang wrote:
> 
> 
> > 2023年4月20日 00:01，Nick Desaulniers <ndesaulniers@google.com> 写道：
> > 
> > On Tue, Apr 18, 2023 at 6:13 AM Thomas Bogendoerfer
> > <tsbogend@alpha.franken.de> wrote:
> >> 
> >> On Fri, Apr 14, 2023 at 09:06:56AM +0100, Jiaxun Yang wrote:
> >>> microMIPS smartMIPS kernel can only be compiled if they are supported
> >>> by toolchain.
> >>> 
> >>> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> >>> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> > 
> > Question: won't the lack of this (patch and rest of the series) hurt
> > our ability to test randconfig builds of ARCH=mips with clang? See
> > also the 0day report from Boris:
> > https://lore.kernel.org/llvm/202304170748.Fg9VIgGd-lkp@intel.com/
> 
> Kconfig experts, Is there any way to generate warning based on Kconfig options?
> So we can let users know there are something went wrong but still allow build to happen.

I do not think there is a way that this can be done within Kconfig
itself but you could do something like arch/x86/Makefile does for
RETPOLINE during archprepare and warn when an option is selected without
a dependency. I envision something like the following but it has not
even been compile tested:

diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index 04e46ec24319..2c3be65ce3cc 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -399,6 +399,11 @@ ifdef CONFIG_MIPS32_O32
 	@$(kecho) '  Checking missing-syscalls for O32'
 	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_flags="-mabi=32"
 endif
+ifdef CONFIG_CPU_HAS_SMARTMIPS
+ifndef CC_HAS_SMARTMIPS
+	$(warning CONFIG_CPU_HAS_SMARTMIPS selected without supported compiler, build may not work)
+endif
+endif
 
 install:
 	$(Q)install -D -m 755 vmlinux $(INSTALL_PATH)/vmlinux-$(KERNELRELEASE)

You could also make that depend on !CONFIG_COMPILE_TEST, as that is a
signal that the user does not intend to run this kernel.

Masahiro might have other comments.

Cheers,
Nathan
