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