Re: [arm64:for-next/kernel-ptrauth 16/18] aarch64-linux-objdump: warning: fs/squashfs/decompressor_multi.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000

From: Amit Kachhap <amit.kachhap@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: kbuild-all@lists.01.org, kbuild test robot <lkp@intel.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	daniel.kiss@arm.com,
	Kristina Martsenko <kristina.martsenko@arm.com>,
	Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Kees Cook <keescook@chromium.org>
Subject: Re: [arm64:for-next/kernel-ptrauth 16/18] aarch64-linux-objdump: warning: fs/squashfs/decompressor_multi.o: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000
Date: Tue, 24 Mar 2020 22:02:16 +0530	[thread overview]
Message-ID: <bf23b903-28f4-226c-49ce-3f761ae848a7@arm.com> (raw)
In-Reply-To: <20200324161507.GA3901@mbp>

On 3/24/20 9:45 PM, Catalin Marinas wrote:
> On Mon, Mar 23, 2020 at 10:36:15PM +0530, Amit Kachhap wrote:
>> 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.
> 
> Are there gcc versions supporting PAC but not generating the
> .note.gnu.property?

Yes GCC older than GCC9 supports PAC without the note (I will find out 
the exact GCC version).

> 
>> 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.
> 
> If there isn't a way to silence the linker or objdump, could we align
> the compiler version we know that generates this note with a minimum
> binutils? Something like:
> 
> 	depends on (GCC_VERSION < X) || (LD_VERSION >= 233...)

Yes this is possible.

> 

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