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* [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
@ 2020-09-28 22:48 Nathan Chancellor
  2020-10-12 21:10 ` Nick Desaulniers
  0 siblings, 1 reply; 6+ messages in thread
From: Nathan Chancellor @ 2020-09-28 22:48 UTC (permalink / raw)
  To: Kees Cook, Ingo Molnar
  Cc: Russell King, linux-arm-kernel, linux-kernel, clang-built-linux,
	Nathan Chancellor, kernel test robot

After turning on warnings for orphan section placement, enabling
CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes
thousands of warnings when clang + ld.lld are used:

$ scripts/config --file arch/arm/configs/multi_v7_defconfig \
                 -d CONFIG_UNWINDER_ARM \
                 -e CONFIG_UNWINDER_FRAME_POINTER
$ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 defconfig zImage
ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being placed in '.ARM.extab.ref.text'
ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed in '.ARM.extab'

These sections are handled by the ARM_UNWIND_SECTIONS define, which is
only added to the list of sections when CONFIG_ARM_UNWIND is set.
CONFIG_ARM_UNWIND is a hidden symbol that is only selected when
CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never
handles these sections. According to the help text of
CONFIG_UNWINDER_ARM, these sections should be discarded so that the
kernel image size is not affected.

Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
Link: https://github.com/ClangBuiltLinux/linux/issues/1152
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/arm/kernel/vmlinux.lds.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 5f4922e858d0..a2c0d96b0580 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -40,6 +40,10 @@ SECTIONS
 		ARM_DISCARD
 #ifndef CONFIG_SMP_ON_UP
 		*(.alt.smp.init)
+#endif
+#ifndef CONFIG_ARM_UNWIND
+		*(.ARM.exidx*)
+		*(.ARM.extab*)
 #endif
 	}
 

base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11
-- 
2.28.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2020-10-14  9:24 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-28 22:48 [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections Nathan Chancellor
2020-10-12 21:10 ` Nick Desaulniers
2020-10-12 21:22   ` Fāng-ruì Sòng
2020-10-12 21:26     ` Kees Cook
2020-10-13  3:26       ` Nathan Chancellor
2020-10-13 22:56         ` Nick Desaulniers

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