Hello,
I'd like to ask a question about target macros of registers. In
mips.h, the fixed registers are defined as follows:
/* By default, fix the kernel registers ($26 and $27), the global
pointer ($28) and the stack pointer ($29). This can change
depending on the command-line options.
Regarding coprocessor registers: without evidence to the contrary,
it's best to assume that each coprocessor register has a unique
use. This can be overridden, in, e.g., override_options() or
CONDITIONAL_REGISTER_USAGE should the assumption be inappropriate
for a particular target. */
#define FIXED_REGISTERS \
{ \
1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, \
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, \
/* COP0 registers */ \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
/* COP2 registers */ \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
/* COP3 registers */ \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 \
}
I'd like to know why mips doesn't define $30 and $31 as fix registers?
And when should they be defined true?
Thanks very much.
Eric.
