David Daney <ddaney@xxxxxxxxxx> writes:
> Ralf Baechle wrote:
>> On Wed, Jun 11, 2008 at 10:04:25AM -0700, David Daney wrote:
>>
>>> The third operand to 'ins' must be a constant int, not a register.
>>>
>>> Signed-off-by: David Daney <ddaney@xxxxxxxxxx>
>>> ---
>>> include/asm-mips/bitops.h | 6 +++---
>>> 1 files changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/asm-mips/bitops.h b/include/asm-mips/bitops.h
>>> index 6427247..9a7274b 100644
>>> --- a/include/asm-mips/bitops.h
>>> +++ b/include/asm-mips/bitops.h
>>> @@ -82,7 +82,7 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *addr)
>>> "2: b 1b \n"
>>> " .previous \n"
>>> : "=&r" (temp), "=m" (*m)
>>> - : "ir" (bit), "m" (*m), "r" (~0));
>>> + : "i" (bit), "m" (*m), "r" (~0));
>>> #endif /* CONFIG_CPU_MIPSR2 */
>>> } else if (cpu_has_llsc) {
>>> __asm__ __volatile__(
>>
>> An old trick to get gcc to do the right thing. Basically at the stage when
>> gcc is verifying the constraints it may not yet know that it can optimize
>> things into an "i" argument, so compilation may fail if "r" isn't in the
>> constraints. However we happen to know that due to the way the code is
>> written gcc will always be able to make use of the "i" constraint so no
>> code using "r" should ever be created.
>>
>> The trick is a bit ugly; I think it was used first in asm-i386/io.h ages ago
>> and I would be happy if we could get rid of it without creating new problems.
>> Maybe a gcc hacker here can tell more?
>
> It is not nice to lie to GCC.
>
> CCing GCC and Richard in hopes that a wider audience may shed some light on the issue.
You _might_ be able to use "i#r" instead of "ri", but I wouldn't
really recommend it. Even if it works now, I don't think there's
any guarantee it will in future.
There are tricks you could pull to detect the problem at compile time
rather than assembly time, but that's probably not a big win. And again,
I wouldn't recommend them.
I'm not saying anything you don't know here, but if the argument is
always a syntactic constant, the safest bet would be to apply David's
patch and also convert the function into a macro. I notice some other
ports use macros rather than inline functions here. I assume you've
deliberately rejected macros as being too ugly though.
Richard
