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

[Philippe Mathieu-Daudé]

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
-fno-common -fPIE
 QEMU_CFLAGS += -fwrapv -fno-strict-aliasing -fno-asynchronous-unwind-tables
 QEMU_CFLAGS += $(call cc-option, $(QEMU_CFLAGS), -fno-stack-protector)
---

> Ack. This warning does more harm than good in here.
>

Patch coming.