PowerPC EABI Registers

3.2.1.  Registers

The 64-bit PowerPC Architecture provides 32 general purpose registers,
each 64 bits wide.  In addition, the architecture provides 32
floating-point registers, each 64 bits wide, and several special
purpose registers.  All of the integer, special purpose, and
floating-point registers are global to all functions in a running
program.  The following table shows how the registers are used.

r0        Volatile register used in function prologs
r1        Stack frame pointer
r2        TOC pointer
r3        Volatile parameter and return value register
r4-r10    Volatile registers used for function parameters
r11       Volatile register used in calls by pointer and as an
          environment pointer for languages which require one
r12       Volatile register used for exception handling and glink code
r13       Reserved for use as system thread ID
r14-r31   Nonvolatile registers used for local variables

f0        Volatile scratch register
f1-f4     Volatile floating point parameter and return value registers
f5-f13    Volatile floating point parameter registers
f14-f31   Nonvolatile registers

LR        Link register (volatile)
CTR       Loop counter register (volatile)
XER       Fixed point exception register (volatile)
FPSCR     Floating point status and control register (volatile)

CR0-CR1   Volatile condition code register fields
CR2-CR4   Nonvolatile condition code register fields
CR5-CR7   Volatile condition code register fields

On processors with the VMX feature.

v0-v1     Volatile scratch registers
v2-v13    Volatile vector parameters registers
v14-v19   Volatile scratch registers
v20-v31   Non-volatile registers
vrsave    Non-volatile 32-bit register