Chapter 29. MIPS Dependent Features

169

2000, 3000, 3900, 4000, 4010, 4100, 4111, vr4120, vr4130, vr4181, 4300, 4400, 4600, 4650, 5000,

rm5200, rm5230, rm5231, rm5261, rm5721, vr5400, vr5500, 6000, rm7000, 8000, rm9000, 10000,

12000, mips32 4k, sb1

 mtune=cpu

Schedule and tune for a particular MIPS cpu. Valid

cpu

values are identical to

 march=cpu

.

 mabi=abi

Record which ABI the source code uses. The recognized arguments are:

32

,

n32

,

o64

,

64

and

eabi

.

 nocpp

This option is ignored. It is accepted for command line compatibility with other assemblers,

which use it to turn off C style preprocessing. With gnu

as

, there is no need for

 nocpp

, because

the gnu assembler itself never runs the C preprocessor.

 construct floats

 no construct floats

The

 no construct floats

option disables the construction of double width floating point

constants by loading the two halves of the value into the two single width floating point registers

that make up the double width register. This feature is useful if the processor support the FR bit

in its status register, and this bit is known (by the programmer) to be set. This bit prevents the

aliasing of the double width register by the single width registers.

By default

 construct floats

is selected, allowing construction of these floating point con 

stants.

 trap

 no break

as

automatically macro expands certain division and multiplication instructions to check for

overflow and division by zero. This option causes

as

to generate code to take a trap exception

rather than a break exception when an error is detected. The trap instructions are only supported

at Instruction Set Architecture level 2 and higher.

 break

 no trap

Generate code to take a break exception rather than a trap exception when an error is detected.

This is the default.

 mpdr

 mno pdr

Control generation of

.pdr

sections. Off by default on IRIX, on elsewhere.

29.2. MIPS ECOFF object code

Assembling for a mips ecoff target supports some additional sections besides the usual

.text

,

.data

and

.bss

. The additional sections are

.rdata

, used for read only data,

.sdata

, used for small data,

and

.sbss

, used for small common objects.

When assembling for ecoff, the assembler uses the

$gp

(

$28

) register to form the address of a "small

object". Any object in the

.sdata

or

.sbss

sections is considered "small" in this sense. For external

objects, or for objects in the

.bss

section, you can use the

gcc  G

option to control the size of objects

addressed via

$gp

; the default value is 8, meaning that a reference to any object eight bytes or smaller