For the
PowerPC architecture, the Linux kernel uses the following registers:
- R1:
- stack pointer
- R2:
- pointer to task_struct for the current task
- R3-R4:
- parameter passing and return values
- R5-R10:
- parameter passing
- R13:
- small data area pointer
- R30:
- GOT pointer
- R31:
- frame pointer
A function can use
r0 and
r3 -
r12 without saving and restoring them.
r13 -
r31 have to be preserved
so they must be saved and restored when you want to use them.
Also,
cr2 -
cr4 must be preserved,
while
cr0,
cr1,
cr5 -
cr7,
lr,
ctr and
xer
can be used without saving & restoring them.
[ Posted Tue, 15 Jul 2003 by Paul Mackerras to
linuxppc-embedded@lists.linuxppc.org ].
See also the (E)ABI specifications for the
PowerPC architecture,
Developing PowerPC Embedded Application Binary Interface (EABI) Compliant Programs
