Re: s390-ccw: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 4/22/21 6:07 PM, Thomas Huth wrote:
> On 22/04/2021 17.52, Stefano Garzarella wrote:
>> On Thu, Apr 22, 2021 at 05:38:26PM +0200, Thomas Huth wrote:
>>> On 22/04/2021 16.31, Philippe Mathieu-Daudé wrote:
>>>> On 4/22/21 2:41 PM, Christian Borntraeger wrote:
>>>>> On 22.04.21 13:47, Thomas Huth wrote:
>>>>>> On 22/04/2021 13.24, Philippe Mathieu-Daudé wrote:
>>>>>>> On 4/22/21 12:30 PM, Peter Maydell wrote:
>>>>>>>> On Thu, 22 Apr 2021 at 11:18, Daniel P. Berrangé
>>>>>>>> <berrange@redhat.com> wrote:
>>>>
>>>>>>> This silents the warning however:
>>>>>>>
>>>>>>> -- >8 --
>>>>>>> diff --git a/pc-bios/s390-ccw/libc.h b/pc-bios/s390-ccw/libc.h
>>>>>>> index bcdc45732d..2dea399904 100644
>>>>>>> --- a/pc-bios/s390-ccw/libc.h
>>>>>>> +++ b/pc-bios/s390-ccw/libc.h
>>>>>>> @@ -19,6 +19,8 @@ typedef unsigned short     uint16_t;
>>>>>>>   typedef unsigned int       uint32_t;
>>>>>>>   typedef unsigned long long uint64_t;
>>>>>>>
>>>>>>> +#pragma GCC diagnostic push
>>>>>>> +#pragma GCC diagnostic ignored "-Wstringop-overflow"
>>>>>>>   static inline void *memset(void *s, int c, size_t n)
>>>>>>>   {
>>>>>>>       size_t i;
>>>>>>> @@ -30,6 +32,7 @@ static inline void *memset(void *s, int c,
>>>>>>> size_t n)
>>>>>>>
>>>>>>>       return s;
>>>>>>>   }
>>>>>>> +#pragma GCC diagnostic pop
>>>>>>
>>>>>> Honestly, that compiler "bug" sounds like it could trigger at any
>>>>>> other spot in the bios code, too, since we are doing lots of direct
>>>>>> accesses to low memory there. I think it's likely best if we shut it
>>>>>> off with -Wno-stringop-overflow in the pc-bios/s390-ccw/Makefile ...
>>>>>> could you please try to add it there?
>>>>>
>>>>
>>>> We are good with:
>>>>
>>>> -- >8 --
>>>> diff --git a/pc-bios/s390-ccw/Makefile b/pc-bios/s390-ccw/Makefile
>>>> index 29fd9019b8..dcec09b6f9 100644
>>>> --- a/pc-bios/s390-ccw/Makefile
>>>> +++ b/pc-bios/s390-ccw/Makefile
>>>> @@ -8,6 +8,9 @@ CFLAGS = -O2 -g
>>>>  quiet-command = $(if $(V),$1,$(if $(2),@printf "  %-7s %s\n" $2 $3 &&
>>>> $1, @$1))
>>>>  cc-option = $(if $(shell $(CC) $1 -S -o /dev/null -xc /dev/null >
>>>> /dev/null \
>>>>               2>&1 && echo OK), $1, $2)
>>>> +cc-c-option = $(if $(shell $(CC) $1 $2 -c -o /dev/null -xc /dev/null \
>>>> +                >/dev/null 2>&1 && echo OK), $2, $3)
>>>>
>>>>  VPATH_SUFFIXES = %.c %.h %.S %.m %.mak %.sh %.rc Kconfig% %.json.in
>>>>  set-vpath = $(if $1,$(foreach PATTERN,$(VPATH_SUFFIXES),$(eval vpath
>>>> $(PATTERN) $1)))
>>>> @@ -30,6 +33,7 @@ OBJECTS = start.o main.o bootmap.o jump2ipl.o sclp.o
>>>> menu.o \
>>>>           virtio.o virtio-scsi.o virtio-blkdev.o libc.o cio.o
>>>> dasd-ipl.o
>>>>
>>>>  QEMU_CFLAGS := -Wall $(filter -W%, $(QEMU_CFLAGS))
>>>> +QEMU_CFLAGS += $(call cc-c-option, $(QEMU_CFLAGS),
>>>> -Wno-stringop-overflow)
>>>>  QEMU_CFLAGS += -ffreestanding -fno-delete-null-pointer-checks
>>>
>>> I think you don't need the "cc-c-option" magic here. Just add the
>>> -Wno-stringop-overflow. All supported versions of GCC and Clang
>>> simply silently ignore unknown -Wno-something options (try e.g. "gcc
>>> -Wno-yadayadayada" on the command line).
>>
>> Clang seems not to like it. It's always a mess to do anything for gcc
>> and clang :-(

I didn't know we could build s390-ccw with clang.

Not with clang-12:

clang version 12.0.0 (Fedora 12.0.0-0.3.rc1.fc34)

warning: unknown warning option '-Wold-style-declaration'; did you mean
'-Wout-of-line-declaration'? [-Wunknown-warning-option]
warning: unknown warning option '-Wimplicit-fallthrough=2'; did you mean
'-Wimplicit-fallthrough'? [-Wunknown-warning-option]
warning: unknown warning option '-Wno-stringop-overflow'; did you mean
'-Wno-shift-overflow'? [-Wunknown-warning-option]
warning: unknown warning option '-Wold-style-declaration'; did you mean
'-Wout-of-line-declaration'? [-Wunknown-warning-option]
warning: unknown warning option '-Wimplicit-fallthrough=2'; did you mean
'-Wimplicit-fallthrough'? [-Wunknown-warning-option]
warning: unknown warning option '-Wno-stringop-overflow'; did you mean
'-Wno-shift-overflow'? [-Wunknown-warning-option]
error: unknown target CPU 'z900'
note: valid target CPU values are: arch8, z10, arch9, z196, arch10,
zEC12, arch11, z13, arch12, z14, arch13, z15

>> Maybe we can set also `-Wno-unknown-warning-option`.
>>
>> $ clang -Wno-stringop-overflow -Werror main.c
>> error: unknown warning option '-Wno-stringop-overflow'; did you mean
>> '-Wno-shift-overflow'? [-Werror,-Wunknown-warning-option]
> 
> D'oh, I was pretty sure that Clang behaves the same with regards to
> -Wno-something, but seems I was wrong, sorry.
> 
> So I think we should simply keep this v1 of Philippe's patch.
> 
> I'll queue it to my s390-ccw branch.

Thanks!

Phil.