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

[Thomas Huth <thuth@redhat.com>]

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).

  Thomas