linux-kernel - Re: A simple question of sys

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Date:	Fri, 17 Sep 2010 11:55:23 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Rofail Qu <rofail@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: A simple question of sys_

On Fri, 17 Sep 2010 14:58:30 +0800 Rofail Qu wrote:

> How to use macro IS_ERR() ?
> 
> It defines as,
> ...
> #define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
> static inline long __must_check IS_ERR(const void *ptr)
> {
> 	return IS_ERR_VALUE((unsigned long)ptr);
> }
> ...
> so when pass x as a pointer and x>=-MAX_ERRNO (including NULL or any
> valid address),
> IS_ERR() will return true!

Since your conclusion is false, some part of your premise must have a problem.
Can you find it?


> IS_ERR(x) seems to use on judge if "x" is a valid error number, right?

Yes, that's what it is for.

> So in sys_execve(),
> ...
>         long error;
> 	char* filename;
> 
> 	filename = getname(name);
> 	error = PTR_ERR(filename);
> 	if (IS_ERR(filename))     // <== should be IS_ERR((void *)error) or other?
> 		return error;
> 	error = do_execve(filename, argv, envp, regs);
> ...
> 
> Where i am wrong?


---
~Randy
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