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From:   Nathan Chancellor <nathan@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>, x86@kernel.org
Cc:     Andy Lutomirski <luto@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        linux-kernel@vger.kernel.org, alsa-devel@alsa-project.org,
        linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
        llvm@lists.linux.dev, Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH 2/2] x86/Kconfig: Do not allow CONFIG_X86_X32_ABI=y with llvm-objcopy
Date:   Mon, 14 Mar 2022 12:48:42 -0700
Message-Id: <20220314194842.3452-3-nathan@kernel.org>
In-Reply-To: <20220314194842.3452-1-nathan@kernel.org>
References: <20220314194842.3452-1-nathan@kernel.org>
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There are two outstanding issues with CONFIG_X86_X32_ABI and
llvm-objcopy, with similar root causes:

1. llvm-objcopy does not properly convert .note.gnu.property when going
   from x86_64 to x86_x32, resulting in a corrupted section when
   linking:

   https://github.com/ClangBuiltLinux/linux/issues/1141

2. llvm-objcopy produces corrupted compressed debug sections when going
   from x86_64 to x86_x32, also resulting in an error when linking:

   https://github.com/ClangBuiltLinux/linux/issues/514

After commit 41c5ef31ad71 ("x86/ibt: Base IBT bits"), the
.note.gnu.property section is always generated when
CONFIG_X86_KERNEL_IBT is enabled, which causes the first issue to become
visible with an allmodconfig build:

  ld.lld: error: arch/x86/entry/vdso/vclock_gettime-x32.o:(.note.gnu.property+0x1c): program property is too short

To avoid this error, do not allow CONFIG_X86_X32_ABI to be selected when
using llvm-objcopy. If the two issues ever get fixed in llvm-objcopy,
this can be turned into a feature check.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/x86/Kconfig | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b903bfcd713c..0f0672d2c816 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2864,6 +2864,11 @@ config IA32_AOUT
 config X86_X32_ABI
 	bool "x32 ABI for 64-bit mode"
 	depends on X86_64
+	# llvm-objcopy does not convert x86_64 .note.gnu.property or
+	# compressed debug sections to x86_x32 properly:
+	# https://github.com/ClangBuiltLinux/linux/issues/514
+	# https://github.com/ClangBuiltLinux/linux/issues/1141
+	depends on $(success,$(OBJCOPY) --version | head -n1 | grep -qv llvm)
 	help
 	  Include code to run binaries for the x32 native 32-bit ABI
 	  for 64-bit processors.  An x32 process gets access to the
-- 
2.35.1