AT&T UNIX™PC Unix System V Users Manual - tenox

A_OUT ( 4 } A-OUT (4)
NAME
a.out - common assembler and link editor output
SYNOPSIS
#include < a.out.h >
DESCRIPTION
The file name a.out is the output file from the assembler a.s(l)
and the link editor ld(l). Both programs will make a. out executable
if there were no errors in assembling or linking and no
unresolved external references.
A common object file consists of a file header, a UNIX system
header, a table of section headers, relocation information,
(optional) line numbers, a symbol table, and a string table. The
order is given below.
File header.
UNIX header.
Section 1 header.
Section n header.
Section 1 data.
Section n data.
Section 1 relocation.
Section n relocation.
Section 1 line numbers.
Section n line numbers.
Symbol table.
String table.
The last three parts (line numbers, symbol table and string table)
may be missing if the program was linked with the -s option of
ld(l) or if the symbol table and relocation bits were removed by
strip(!). Also note that the relocation information will be absent
if there were no unresolved external references after linking. The
string table exists only if the symbol table contains symbols with
names longer than eight characters.
The sizes of each section (contained in the header, discussed
below) are in bytes and are even.
When an a.out file is loaded into memory for execution, three logical
segments are set up: the text segment, the data segment (initialized
data followed by uninitialized, the latter actually being
initialized to all O's), and a stack. The text segment begins at
location OxOOOO in the core image. The header is never loaded
except for magic 0413 files created with the -F option of ld(l). If
the magic number (the first field in the operating system header)
is 407 (octal), it indicates that the text segment is not to be
write-protected or shared, so the data segment will be contiguous
with the text segment. If the magic number is 410 (octal), the
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