On Mon, 7 May 2012, Hill, Steven wrote:
> I will certainly remove CONFIG_CPU_HAS_LLSC, thank you. I attempted to
> enable 'cpu_has_clo_clz' for SEAD-3, but it breaks my microMIPS-only
> kernel builds. Specifically, since microMIPS LL/SC instructions do not
> have 16-bit address offsets, in the '__cmpxchg_asm' macro function I get
> constraint errors because then the assembler has to use the %LO register
> in order to calculate the offset address. I am going to hold off on
> enabling the option until after the 3.5 release and then revisit for a
> solution. Thank you.
It's OK to ask. :) Try using the "YC" constraint, this piece:
int test(void *p)
{
int i;
__asm__ __volatile__("ll\t%0,%1" : "=r" (i) : "YC" (*p));
return i;
}
assembles to:
ll $2,0($4)
jrc $31
for me (with "-O2 -mmicromips").
You may have to factor in backwards compatibility -- while "YC" is
supported both in the microMIPS and the standard MIPS mode, switching the
width of the immediate offset between 12 and 16 bits as appropriate, it's
certainly a new constraint older compilers did not support. I suggest
using a macro, as usually, you can use some existing examples as a
reference, e.g. <asm/compiler.h> (you know where to place this stuff now
too :) ).
Maciej
