On Wed, Jan 6, 2021 at 2:07 PM Kees Cook [off-list ref] wrote:

On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:

quoted

Discard GNU attributes at link time as kernel doesn't use it at all.
Solves a dozen of the following ld warnings (one per every file):

mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes'
from `arch/mips/kernel/head.o' being placed in section
`.gnu.attributes'
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes'
from `init/main.o' being placed in section `.gnu.attributes'

Misc: sort DISCARDS section entries alphabetically.

Hmm, I wonder what is causing the appearance of .eh_frame? With help I
tracked down all the causes of this on x86, arm, and arm64, so that's
why it's not in the asm-generic DISCARDS section. I suspect this could
be cleaned up for mips too?

On x86, 003602ad5516e59940de42e44c8d8033387bb363 "x86/*/Makefile: Use
-fno-asynchronous-unwind-tables to suppress .eh_frame sections"
noticed that some Makefiles
redefined KBUILD_CFLAGS and dropped -fno-asynchronous-unwind-tables.
Maybe mips has similar issues.

Similarly for .gnu.attributes. What is generating that? (Or, more
specifically, why is it both being generated AND discarded?)

-Kees

gcc/config/mips/mips.c
https://github.com/gcc-mirror/gcc/blob/master/gcc/config/mips/mips.c#L9965
.gnu_attribute 4, 0 does not produce .gnu.attributes
(SHT_GNU_ATTRIBUTES) but there are likely code paths that
a non-zero value is used... So .gnu_attributes is likely needed to be excluded.

quoted

Signed-off-by: Alexander Lobakin <redacted>
---
 arch/mips/kernel/vmlinux.lds.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index 83e27a181206..5d6563970ab2 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S

@@ -221,9 +221,10 @@ SECTIONS
              /* ABI crap starts here */
              *(.MIPS.abiflags)
              *(.MIPS.options)
+             *(.eh_frame)
+             *(.gnu.attributes)
              *(.options)
              *(.pdr)
              *(.reginfo)
-             *(.eh_frame)
      }
 }
--

2.30.0

--
Kees Cook

-- 
宋方睿