[PATCH 2/2] x86/Kconfig: Do not allow CONFIG_X86_X32_ABI=y with llvm-objcopy

Nathan Chancellor
2022-03-14T19:50:52Z

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