[kvm-ppc-devel] The default for char Literals differ in signedness

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

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 ?
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)?

Whats your opinion on that?

-- 

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

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