Chapter 2. Overview

17

is itself synthesized from other files.

as

understands the

#

directives emitted by the

gcc

preprocessor.

See also Section 8.37

.file string

.

2.6. Output (Object) File

Every time you run

as

it produces an output file, which is your assembly language program translated

into numbers. This file is the object file. Its default name is

a.out

, or

b.out

when

as

is configured

for the Intel 80960. You can give it another name by using the

 o

option. Conventionally, object file

names end with

.o

. The default name is used for historical reasons: older assemblers were capable

of assembling self contained programs directly into a runnable program. (For some formats, this isn't

currently possible, but it can be done for the

a.out

format.)

The object file is meant for input to the linker

ld

. It contains assembled program code, information to

help

ld

integrate the assembled program into a runnable file, and (optionally) symbolic information

for the debugger.

2.7. Error and Warning Messages

as

may write warnings and error messages to the standard error file (usually your terminal). This

should not happen when a compiler runs

as

automatically. Warnings report an assumption made so

that

as

could keep assembling a flawed program; errors report a grave problem that stops the assembly.

Warning messages have the format

file_name:NNN :Warning Message Text

(where NNN is a line number). If a logical file name has been given (Section 8.37

.file string

) it is

used for the filename, otherwise the name of the current input file is used. If a logical line number was

given (Section 8.54

.line line number

) then it is used to calculate the number printed, otherwise

the actual line in the current source file is printed. The message text is intended to be self explanatory

(in the grand Unix tradition).

Error messages have the format

file_name:NNN :FATAL:Error Message Text

The file name and line number are derived as for warning messages. The actual message text may be

rather less explanatory because many of them aren't supposed to happen.