gnu-assembler 1.1 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 assembler.
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 addressing modes that are standard to a particular archi-
tecture. You may want to consult the manufacturer’s machine architecture manual for this
information.
1.2 The GNU Assembler
gnu as is really a family of assemblers. If you use (or have used) the gnu assembler on
one architecture, 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
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