An error of gcc-ss-20030303

An error of gcc-ss-20030303

[Jie Zhang]

The following code is copied from spinlock.c in uClibc (after 
preprocessing and 'inline' after static removed):

static void __pthread_release(int * spinlock)
{
  asm ("" : : : "memory");
  *spinlock = 0;
  __asm __volatile ("" : "=m" (*spinlock) : "0" (*spinlock));
}

When compiled using gcc-3.0.2, no error is reported. But gcc-3.2 and 
gcc-ss-20030303 report the follwing error:

t.c: In function `__pthread_release':
t.c:5: inconsistent operand constraints in an `asm'

I dump the rtl using -dr and find that gcc-3.0.2 uses a pseudo register 
to hold the address of 'spinlock' and the output operand and input 
operand of __asm__ use the same register. But gcc-ss-20030303 uses two 
pseudo registers for the output operand and input operand of __asm__ 
respectively, both pseudo registers hold the same value -- the address 
of 'spinlock'. Then when checking the constraints, gcc reports the error.

Is it a bug of gcc-3.2.x and gcc-3.3? Or the above __asm__ usage is 
wrong in gcc-3.2.x and gcc-3.3? I think gcc-3.0.2 is right?

- Jie

Re: An error of gcc-ss-20030303

[tm_gccmail]

On Wed, 23 Apr 2003, Jie Zhang wrote:

> The following code is copied from spinlock.c in uClibc (after 
> preprocessing and 'inline' after static removed):
> 
> static void __pthread_release(int * spinlock)
> {
>   asm ("" : : : "memory");
>   *spinlock = 0;
>   __asm __volatile ("" : "=m" (*spinlock) : "0" (*spinlock));
> }
> 

Why not use a pointer to a volatile int?

Toshi

Re: An error of gcc-ss-20030303

[Richard Henderson]

On Wed, Apr 23, 2003 at 03:41:45PM +0800, Jie Zhang wrote:
>  __asm __volatile ("" : "=m" (*spinlock) : "0" (*spinlock));

Don't use matching constraints on memories.


r~

Re: An error of gcc-ss-20030303

[Jie Zhang]

Richard Henderson wrote:

> On Wed, Apr 23, 2003 at 03:41:45PM +0800, Jie Zhang wrote:
>  
>
>> __asm __volatile ("" : "=m" (*spinlock) : "0" (*spinlock));
>>   
>
>
> Don't use matching constraints on memories.
>  
>
The problem is solved by changing this line into

__asm __volatile ("" : "+m" (*spinlock));

I should have read the document more carefully :-P
Thanks all!

- Jie