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

[Thomas Huth]

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