David Daney <ddaney.cavm@xxxxxxxxx> writes:
> On 12/18/2014 07:09 AM, Markos Chandras wrote:
>> MIPS R6 changed the opcodes for LL/SC instructions and reduced the
>> offset field to 9-bits. This has some undesired effects with the "m"
>> constrain since it implies a 16-bit immediate. As a result of which,
>> add a register ("r") constrain as well to make sure the entire address
>> is loaded to a register before the LL/SC operations. Also use macro
>> to set the appropriate ISA for the asm blocks
>>
>
> Has support for MIPS R6 been added to GCC?
>
> If so, that should include a proper constraint to be used with the new
> offset restrictions. We should probably use that, instead of forcing
> to a "r" constraint.
>
>> Cc: Matthew Fortune <Matthew.Fortune@xxxxxxxxxx>
>> Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx>
>> ---
>> arch/mips/include/asm/atomic.h | 50 +++++++++++++++++++++---------------------
>> 1 file changed, 25 insertions(+), 25 deletions(-)
>>
>> diff --git a/arch/mips/include/asm/atomic.h b/arch/mips/include/asm/atomic.h
>> index 6dd6bfc607e9..8669e0ec97e3 100644
>> --- a/arch/mips/include/asm/atomic.h
>> +++ b/arch/mips/include/asm/atomic.h
>> @@ -60,13 +60,13 @@ static __inline__ void atomic_##op(int i, atomic_t * v) \
>> \
>> do { \
>> __asm__ __volatile__( \
>> - " .set arch=r4000 \n" \
>> - " ll %0, %1 # atomic_" #op "\n" \
>> + " .set "MIPS_ISA_ARCH_LEVEL" \n" \
>> + " ll %0, 0(%3) # atomic_" #op "\n" \
>> " " #asm_op " %0, %2 \n" \
>> - " sc %0, %1 \n" \
>> + " sc %0, 0(%3) \n" \
>> " .set mips0 \n" \
>> : "=&r" (temp), "+m" (v->counter) \
>> - : "Ir" (i)); \
>> + : "Ir" (i), "r" (&v->counter)); \
>
> You lost the "m" constraint, but are still modifying memory. There is
> no "memory" clobber here, so we are no longer correctly describing
> what is happening.
Rather than add a blanket "memory" clobber, it's better to keep the old
memory operand even if it is never used. GCC will still assume it has
been modified.
--
Måns Rullgård
mans@xxxxxxxxx
