[Qemu-devel] Re: [kvm-ppc-devel] The default for char Literals differ in signedness between platforms causing us a lot of warnings

[Qemu-devel] Re: [kvm-ppc-devel] The default for char Literals differ in signedness between platforms causing us a lot of warnings

[Christian Ehrhardt]

Hi,
the following discussion is from kvm-ppc-devel, but it is actually an qemu discussion so I move th topic to qemu-devel.
The original thread is cited in the mail below, in short the issue is the following:

Newer gcc versions generate warnings about implicit casts between different signed pointers.
That hits a lot of qemu code at least what I saw it compiling for ppc or x86.
So my question is, is there already a preferred qemu approach to get rid of these warnings
either the -Wno-pointer-sign solution like in the kernel or something else (I did not find
anything like that in the latest cvs snapshot or on this list)?

--- thread from kvm-ppc-devel ---

Jimi Xenidis wrote:
> 
> On Jan 11, 2008, at 10:04 AM, Hollis Blanchard wrote:
> 
>> On Fri, 2008-01-11 at 14:14 +0100, Christian Ehrhardt wrote:
>>> Hi,
>>> maybe its an issue of my build environment only, but when I compile
>>> kvm-userspace for our platform I see a lot of warnings like that in
>>> the qemu code:
>>>
>>>     warning: pointer targets in passing argument 3 of
>>> 'PPC_NVRAM_set_params' differ in signedness
>>>
>>> The reason is that some code defines function prototypes and variables
>>> with the type "const unsigned char*" and then assigns a literal like
>>> "PPC" to it. But per default our platform seems to have "const signed
>>> char*" for literals and so we get a lot of annoying warnings. E.g.
>>> nearly every line in qemu/target-ppc/translate.c.
>>>
>>> Should we do anything to prevent these Warnings or do you even see
>>> those ?
>>
>> That warning only appears in recent versions of gcc. In fact I believe
>> there are 3 different types: char *, unsigned char *, and signed char *,
>> and implicitly casting between them generates the warnings. :(
>>
>>>[...]
>>
>> It's a qemu issue. If you want to fix it, you should bring it up on
>> qemu-devel and see what they think about it.
> 
> this is what:
> # disable pointer signed / unsigned warnings in gcc 4.0
> KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
> 
> In linux/Makefile is for.
> -JX

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization

Re: [Qemu-devel] Re: [kvm-ppc-devel] The default for char Literals differ in signedness between platforms causing us a lot of warnings

[Andre Przywara]

Christian,

 > Newer gcc versions generate warnings about implicit casts between
 > different signed pointers.
 > That hits a lot of qemu code at least what I saw it compiling for ppc
 > or x86.
 > So my question is, is there already a preferred qemu approach to get
 > rid of these warnings
 > either the -Wno-pointer-sign solution like in the kernel or something
 > else (I did not find
 > anything like that in the latest cvs snapshot or on this list)?

I fixed some of these issues in qemu at least for x86[1][2], those were 
commited mid of December[3] . I ported these over to Xen and posted it 
there[4]. I don't know what's the ultimate policy regarding these 
problems, my solution is:
1. Change the type whenever possible.
2. Introduce casts if 1. is not applicable or would introduce more 
back-castings.

Regards,
Andre.

[1] QEMU first proposal (all in one file) with comments:
http://lists.gnu.org/archive/html/qemu-devel/2007-11/msg00827.html
[2] QEMU reworked version (splitted up to address multiple issues)
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00146.html
[3] QEMU commits:
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00417.html
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00420.html
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00448.html
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00452.html
[4] Xen devel post 
http://lists.xensource.com/archives/html/xen-devel/2008-01/msg00185.html

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 277-84917
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