Re: PATCH - x86-64 signed-compare bug, was Re: select() setting ERESTARTNOHAND (514).

[Denis Vlasenko]

On Thursday 11 January 2007 02:02, Neil Brown wrote:
> If regs->rax is unsigned long, then I would think the compiler would
> be allowed to convert
> 
>    switch (regs->rax) {
> 	case -514 : whatever;
>    }
> 
> to a no-op, as regs->rax will never have a negative value.

In C, you never actually compare different types. They always
promoted to some common type first.

both sides of (impicit) == here get promoted to "biggest" integer,
in this case, to unsigned long. "-514" is an int, so it gets
sign extended to the width of "long" and then converted to
unsigned long.
--
vda
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/