Re: somebody dropped a (warning) bomb

Sergei Organov
2007-02-19T12:17:24Z

Bodo Eggert <7eggert@gmx.de> writes:
> On Fri, 16 Feb 2007, Sergei Organov wrote:

[...]

> I'll say it again: Either the code using unspecified chars is correct, or
> it isn't. If it's correct, neither using with signed nor with unsigned
> chars is a bug and you should not warn at all, and if it's not correct,
> you should always warn. Instead, gcc warns on "code compiles for
> $arch".

Here is where we disagree. In my opinion, no matter what the sign of
char for given architecture is, it's incorrect to pass either "signed
char*" or "unsigned char*" argument to a function expecting "char*".

>> > Therefore it's either always wrong to call your char* function with char*,
>> > unsigned char* _and_ signed char unless you can guarantee not to overflow any
>> > of them, or it's always correct to call char* functions with any kind
>> > of these.
>>
>> How are you sure those who wrote foo(char*) agrees with your opinion or
>> even understands all the involved issues?
>
> Let's asume we have this piece of buggy code. We compile it on an unsigned
> char architecture. No warning. *BOOM*

There should be warning, -- that's my point. "char" is different. "char"
is distinct from either "signed char" or "unsigned char". Always. At
least it's how C is defined.

> Let's asume there is correct code, and we use it as designed:
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: real issue
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: Wrong arch
> <scroll off screen/>
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: Wrong arch
> Warning: Wrong arch
>
> You don't see "real issue". *BOOM*
>
>
> What can you do about this warning? Let's asume we cast everywhere:

I already gave an answer in response to Linus:

static inline size_t ustrlen(const unsigned char *s)
{
return strlen((const char *)s);
}

>
> struct foo * p;
> printf(strlen(char*)p); *BOOM*

printf(ustrlen(p)); *NO BOOM*
unsigned char* u;
printf(ustrlen(u)); *NO WARNING*

-- Sergei.