linux-kernel - Re: [PATCH 1/2] ix86: adjust asm constraints in atomic64 wrappers

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Date:	Wed, 18 Jan 2012 16:57:09 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<mingo@...e.hu>, "eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	<tglx@...utronix.de>, <luca@...a-barbieri.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ix86: adjust asm constraints in atomic64
 wrappers

>>> On 18.01.12 at 17:45, "H. Peter Anvin" <hpa@...or.com> wrote:
> On 01/18/2012 06:22 AM, Jan Beulich wrote:
>>  
>> +#ifndef __ATOMIC64_EXPORT
>> +/*
>> + * Don't declare these as functions, even though they are - due to their
>> + * non-standard calling conventions they can't be called by C code anyway.
>> + */
>> +#define __ATOMIC64_EXPORT(sym) extern const atomic64_t atomic64_##sym[]
>> +#endif
>> +
> 
> This is obviously bogus.  They are still functions even if they are not
> callable by C.  In particular, they are NOT in any shape, way, or form
> arrays of type const atomic64_t; if you want to assign them to a
> "generic memory type" they would be const char, but there is no reason

I wanted to make sure that the symbol CRC at least tracks the
atomic64_t type.

> to declare them as anything other than executable code.  Yes, it would
> be wrong to call them, but so would calling any other function that is
> inappropriate.
> 
> For functions with nonstandard calling conventions it is normal to
> declare them as void foo(void);

For the above, I'd like to keep atomic64_t in the signature. Would
void foo(atomic64_t, ...) be acceptable?

> It may be a good idea to prefix these symbols with __ though.

But not in this patch. (Can't resist to add that if you think it should
be this way, why did you not make it a condition for accepting the 
original patch, which you committed?)

Jan

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