Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Tiezhu Yang <yangtiezhu@loongson.cn>
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Cc:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Xuefeng Li <lixuefeng@loongson.cn>
Subject: [PATCH] MIPS: Add comment about CONFIG_MIPS32_O32 in loongson3_defconfig when build with Clang
Date:   Thu,  4 Mar 2021 09:15:44 +0800
Message-Id: <1614820544-10686-1-git-send-email-yangtiezhu@loongson.cn>
Precedence: bulk

When build kernel with Clang [1]:

$ make CC=clang loongson3_defconfig
$ make CC=clang

there exists the following error:

  Checking missing-syscalls for O32
  CALL    scripts/checksyscalls.sh
error: ABI 'o32' is not supported on CPU 'mips64r2'
make[1]: *** [Kbuild:48: missing-syscalls] Error 1
make: *** [arch/mips/Makefile:419: archprepare] Error 2

This is a known bug [2] with Clang, as Simon Atanasyan said,
"There is no plan on support O32 for MIPS64 due to lack of
resources".

It is not a good idea to remove this config due to GCC works
well, so add comment to point out this bug and suggest the
users to remove CONFIG_MIPS32_O32=y in defconfig when build
kernel with Clang.

[1] https://www.kernel.org/doc/html/latest/kbuild/llvm.html
[2] https://bugs.llvm.org/show_bug.cgi?id=38063

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 arch/mips/configs/loongson3_defconfig | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/mips/configs/loongson3_defconfig b/arch/mips/configs/loongson3_defconfig
index 0e79f81..cacf9dd 100644
--- a/arch/mips/configs/loongson3_defconfig
+++ b/arch/mips/configs/loongson3_defconfig
@@ -35,6 +35,9 @@ CONFIG_NUMA=y
 CONFIG_SMP=y
 CONFIG_HZ_256=y
 CONFIG_KEXEC=y
+# Please remove CONFIG_MIPS32_O32=y when build with Clang
+# due to "ABI 'o32' is not supported on CPU 'mips64r2'",
+# https://bugs.llvm.org/show_bug.cgi?id=38063
 CONFIG_MIPS32_O32=y
 CONFIG_MIPS32_N32=y
 CONFIG_VIRTUALIZATION=y
-- 
2.1.0