Hi Catalin,

On 3/23/20 5:18 PM, Catalin Marinas wrote:
> On Sat, Mar 21, 2020 at 12:28:06PM +0800, kbuild test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/kernel-ptrauth
>> head:   3b446c7d27ddd06342901bb35211363f6944291a
>> commit: 74afda4016a7437e6e425c3370e4b93b47be8ddf [16/18] arm64: compile the kernel with ptrauth return address signing
>> config: arm64-randconfig-a001-20200321 (attached as .config)
>> compiler: aarch64-linux-gcc (GCC) 9.2.0
>> reproduce:
>>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>          chmod +x ~/bin/make.cross
>>          git checkout 74afda4016a7437e6e425c3370e4b93b47be8ddf
>>          # save the attached .config to linux build tree
>>          GCC_VERSION=9.2.0 make.cross ARCH=arm64
>>
>> If you fix the issue, kindly add following tag
>> Reported-by: kbuild test robot <lkp@intel.com>
>>
>> All warnings (new ones prefixed by >>):
>>
>>>> aarch64-linux-objdump: warning: fs/squashfs/decompressor_multi.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000
>> --
>>>> aarch64-linux-objdump: warning: drivers/gpio/gpio-bt8xx.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000
> 
> Just to make sure I understand the cause of this warning: gcc generates
> a .note.gnu.property when PAC is enabled for the kernel but binutils
> doesn't understand it. Is there a way to check for this via the Kconfig
> options?

Yes you are right. In this case the binutils version lesser than 2.33 do 
not recognize the GNU_PROPERTY_AARCH64_FEATURE_1_PAC property.
I tried somethings like below but could not find a good way to generate
error via Kconfig for this warning.

~/linux$ echo "int main(void) {return 0;}" > tmp.c | aarch64-linux-gcc 
-Wall -Werror -nostdlib -mbranch-protection=pac-ret+leaf -e main tmp.c 
-o tmp

~0day/gcc-9.2.0-nolibc/aarch64-linux/bin/../lib/gcc/aarch64-linux/9.2.0/../../../../aarch64-linux/bin/ld: 
warning: /tmp/ccExLvun.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000

~/linux$ echo $?
~/linux$ 0

However we can disable pauth in this case by checking linker version
and GNU_PROPERTY feature as,
(readelf -S --wide tmp.o | grep .note.gnu.property) && (ld-ifversion -ge 
233000000).

But I feel disabling pauth in this case seems too aggressive as the 
current way do not break any functionality even though it generates 
confusing warning messages.

Cheers,
Amit
> 

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