Chapter 2. Overview

15

 relax |  no relax

Enable or disable instruction relaxation. This is enabled by default. Note: In the current imple 

mentation, these options also control whether assembler optimizations are performed, making

these options equivalent to

 generics

and

 no generics

.

 generics |  no generics

Enable or disable all assembler transformations of Xtensa instructions. The default is

 generics

;

 no generics

should be used only in the rare cases when the instructions must

be exactly as specified in the assembly source.

 text section literals |  no text section literals

With

 text section literals

, literal pools are interspersed in the text section. The default

is

 no text section literals

, which places literals in a separate section in the output file.

 target align |  no target align

Enable or disable automatic alignment to reduce branch penalties at the expense of some code

density. The default is

 target align

.

 longcalls |  no longcalls

Enable or disable transformation of call instructions to allow calls across a greater range of

addresses. The default is

 no longcalls

.

2.1. Structure of this Manual

This manual is intended to describe what you need to know to use gnu

as

. We cover the syntax

expected in source files, including notation for symbols, constants, and expressions; the directives

that

as

understands; and of course how to invoke

as

.

This manual also describes some of the machine dependent features of various flavors of the assem 

bler.

On the other hand, this manual is not intended as an introduction to programming in assembly

language  let alone programming in general! In a similar vein, we make no attempt to introduce the

machine architecture; we do not describe the instruction set, standard mnemonics, registers or address 

ing modes that are standard to a particular architecture. You may want to consult the manufacturer's

machine architecture manual for this information.

2.2. The GNU Assembler

gnu

as

is really a family of assemblers. If you use (or have used) the gnu assembler on one archi 

tecture, you should find a fairly similar environment when you use it on another architecture. Each

version has much in common with the others, including object file formats, most assembler directives

(often called pseudo ops) and assembler syntax.

as

is primarily intended to assemble the output of the gnu C compiler

gcc

for use by the linker

ld

.

Nevertheless, we've tried to make

as

assemble correctly everything that other assemblers for the same

machine would assemble. Any exceptions are documented explicitly (Chapter 9 Machine Dependent

Features). This doesn't mean

as

always uses the same syntax as another assembler for the same

architecture; for example, we know of several incompatible versions of 680x0 assembly language

syntax.

Unlike older assemblers,

as

is designed to assemble a source program in one pass of the source file.

This has a subtle impact on the .org directive (Section 8.65

.org new lc, fill

).