lkml.org 
[lkml]   [2011]   [Jan]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
Date
On Sun, Jan 02 2011, Pavel Machek wrote:

>> > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
>> > index 6470f63..155ec10 100644
>> > --- a/drivers/char/hvc_dcc.c
>> > +++ b/drivers/char/hvc_dcc.c
>> > @@ -33,8 +33,7 @@
>> > static inline u32 __dcc_getstatus(void)
>> > {
>> > u32 __ret;
>> > -
>> > - asm("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg"
>> > + asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg"
>> > : "=r" (__ret) : : "cc");
>> >
>> > return __ret;
>
> Is volatile needed here? If __dcc_getstatus() return value is
> discarded, we want assembly discarded, right?

That's not really the issue being fixed. Without the volatile, the
compiler is free to cache and reuse a previously loaded status value.
It is important that the status be read each time.

I don't think there is a way of indicating that assembly needs to happen
for each use, but that it is OK to discard if the value isn't used.
'volatile' is a bit overloaded.

--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


\
 
 \ /
  Last update: 2011-01-02 19:53    [W:0.983 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site