Re: Build regressions/improvements in v6.2-rc4

[Guenter Roeck <linux@roeck-us.net>]

On 1/17/23 00:57, Heiko Carstens wrote:
> On Mon, Jan 16, 2023 at 10:41:27AM -0800, Guenter Roeck wrote:
>> On Mon, Jan 16, 2023 at 05:40:00PM +0100, Heiko Carstens wrote:
>>> On Mon, Jan 16, 2023 at 01:36:34PM +0100, Geert Uytterhoeven wrote:
>>>> On Mon, 16 Jan 2023, Geert Uytterhoeven wrote:
>>>>> JFYI, when comparing v6.2-rc4[1] to v6.2-rc3-8-g1fe4fd6f5cad346e[3], the summaries are:
>>>>>   - build errors: +1/-5
>>>>
>>>>    + /kisskb/src/include/linux/fortify-string.h: error: '__builtin_memcpy' reading 128 bytes from a region of size 0 [-Werror=stringop-overread]:  => 57:33
>>>>
>>>> s390x-gcc11/s390-allmodconfig
>>>>
>>>> /kisskb/src/arch/s390/kernel/setup.c: In function 'setup_lowcore_dat_on':
>>>> /kisskb/src/include/linux/fortify-string.h:57:33: error: '__builtin_memcpy' reading 128 bytes from a region of size 0 [-Werror=stringop-overread]
>>>>     57 | #define __underlying_memcpy     __builtin_memcpy
>>>>        |                                 ^
>>>> /kisskb/src/include/linux/fortify-string.h:578:9: note: in expansion of macro '__underlying_memcpy'
>>>>    578 |         __underlying_##op(p, q, __fortify_size);                        \
>>>>        |         ^~~~~~~~~~~~~
>>>> /kisskb/src/include/linux/fortify-string.h:623:26: note: in expansion of macro '__fortify_memcpy_chk'
>>>>    623 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
>>>>        |                          ^~~~~~~~~~~~~~~~~~~~
>>>> /kisskb/src/arch/s390/kernel/setup.c:526:9: note: in expansion of macro 'memcpy'
>>>>    526 |         memcpy(abs_lc->cregs_save_area, S390_lowcore.cregs_save_area,
>>>>        |         ^~~~~~
>>>>
>>>> Looks like this was "'__builtin_memcpy' offset [0, 127] is out of the bounds
>>>> [0, 0]" before.
>>>
>>> Thanks for reporting. Of course this doesn't happen with gcc-12, and
>>> this code will be rewritten with the next merge window anyway.
>>> But to workaround this with gcc-11, we could go with the below:
>>>
>>
>> This is because of
>>
>> #define S390_lowcore (*((struct lowcore *) 0))
>>
>> and is fixed with something like
>>
>> #define S390_lowcore (*((struct lowcore *) absolute_pointer(0)))
>>
>> See commit f6b5f1a56987 ("compiler.h: Introduce absolute_pointer macro").
> 
> Yes, I'm aware of that. However absolute_pointer() is not an option for
> S390_lowcore. See also commit f0be87c42cbd ("gcc-12: disable
> '-Warray-bounds' universally for now") and the referenced s390 commit.
> 

Interesting. It works (builds) just fine for me after the above suggested
change.

Guenter

>> The problem is only seen with gcc 11.2. I don't see it with 11.3 or 12.2.
> 
> FWIW, the compile warning is seen with gcc 11.1 and 11.2, but not with any
> other compiler. Given that this isn't the first report, I'm tempted to
> workaround this now.