Re: [kvm-ppc-devel] The default for char Literals differ

[Hollis Blanchard <hollisb@us.ibm.com>]

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. :(

> We could search for compiler options like
> -fsigned-string/-funsigned-string (did not help here in a quick test)
> or patch qemu code to our signedness, but this would need extensive
> tests to prevent that we fix it for us and create the same warning for
> others.
> The gcc developers here said a literal is defined as "array of char"
> which obviously can be cast implicitly to "const char*" and the
> platform decides if it is signed or unsigned - at least most library
> functions solve this by using "const char*" without signedness. That
> way the compilation should work for everyone because the
> variables/prototypes are automatically mapped to the platform defined
> signedness as the literals are too.
> 
> The questions for our project are:
> - do we need that fixed?
> - is it our job to fix that?
> - Which approach should we go (maybe I missed some possible
> solutions)?

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.

-- 
Hollis Blanchard
IBM Linux Technology Center


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