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7. Application Binary Interface
NII-PRG | 2018.04.18
7.3. Register Usage
The ABI adds additional usage conventions to the Nios II register file defined in the
Programming Model chapter of the Nios II Processor Reference Handbook.
Table 83.
Nios II ABI Register Usage
Register
Name
r0
zero
r1
at
r2
r3
r4
r5
r6
r7
r8
r9
r10
r11
r12
r13
r14
r15
r16
r17
r18
r19
r20
r21
r22
r23
(41)
A function can use one of these registers if it saves it first. The function must restore the
register's original value before exiting.
(42)
In the GNU Linux operating system,
is available as a callee-saved general-purpose register.
Used by
Callee
(41)
Compiler
Saved
v
0x00000000
Assembler temporary
v
Return value (least-significant 32 bits)
v
Return value (most-significant 32 bits)
v
Register arguments (first 32 bits)
v
Register arguments (second 32 bits)
v
Register arguments (third 32 bits)
v
Register arguments (fourth 32 bits)
v
Caller-saved general-purpose registers
v
v
v
v
v
v
v
v
v
Callee-saved general-purpose registers
v
v
v
v
v
v
v
v
v
v
(42)
v
(43)
v
r22
Normal Usage
points to the global offset table (GOT). Otherwise, it
continued...
Nios II Processor Reference Guide
147
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