⟦4fbb35786⟧

TextFile

.ig
	@(#)a.out.5	2.1	7/1/84
	@(#)Copyright (C) 1983 by National Semiconductor Corp.
..
.\" qgrind -f a.out.5 > grind.a.out.5 
.\" qtroff -t ~vgasio/tmac.an grind.a.out.5 > ../QTROFFED/a.out.5
.ds GE \s-2GENIX\s0
.ds Ge G\s-2ENIX\s0
.TH A.OUT 5 
.SH NAME
a.out \- assembler and link editor output (a16.out when cross-support)
.SH SYNOPSIS
.B #include <a.out.h>
.SH DESCRIPTION
.I A.out 
is the output file of the assembler 
.IR as (1)
and the link editor
.IR ld (1).
Both programs make
.I a.out 
executable if there were
no errors and no unresolved external references.
.PP
The terms ``address'' and ``location'' refer to addresses within the 
address space.
The term ``position'' refers to a point in the 
.I a.out 
file.
Layout information for the NS32016 is:
.sp
.br
.nf
'\"	Do some dancing around to make things look nice...
'\"		The following section appears twice,
'\"		first in an nroff version and then
'\"		in a troff version.  We have to do it this way
'\"		to avoid compromising appearance in either formatter.
.if n \{\
.	ta 8 +8 +8 +8 +8 +8 +8 +8 +8 +8 +8 +8 +8 +8 +8 +8
/*
 * A.out file layout information:
 *
 * "+" indicates an addition to the Berkeley 4.1 format.
 *
 * Note:
 *	This file contains only an incomplete description of
 *	information present in an a.out file; it omits symbol
 *	table definitions.
 *
 *	Complete symbol table definitions reside in <stab.h> and
 *	simplified definitions in <nlist.h>.  These sets of
 *	definitions are not fully compatible with each other; symbol
 *	table information as defined in <nlist.h> does not correspond
 *	directly to a.out file contents, but instead is obtained by
 *	translating such information with nlist(3).
 */

/*
 * Header prepended to each a.out file.
 */
struct exec {
	 long	a_magic;	/* magic number			   */
unsigned long	a_text;		/* size of text segment		   */
unsigned long	a_data;		/* size of initialized data	   */
unsigned long	a_bss;		/* size of uninitialized data	   */
unsigned long	a_syms;		/* size of symbol table		   */
unsigned long	a_entry;	/* entry point address		   */
unsigned long	a_entry_mod;	/*+entry point - mod number	   */
unsigned long	a_trsize;	/* size of text relocation -
				 * specifies relocation of link
				 * tables at present		   */
unsigned long	a_drsize;	/* size of data relocation -
				 * current assembler sets to zero  */
unsigned long	a_mod;		/*+size of mod table within text   */
unsigned long	a_link;		/*+size of link table within text  */
unsigned long	a_strings;	/*+size of string table		   */
unsigned long	a_text_addr;	/*+address of text section in
				 *+address space                   */
unsigned long	a_mod_addr;	/*+address of mod table in
				 *+address space                   */
unsigned long	a_dat_addr;	/*+address of data section in
				 *+address space                   */
};

#define OMAGIC	0407		/* old impure format		   */
#define NMAGIC	0410		/* read-only text		   */
#define ZMAGIC	0413		/* demand load format		   */
#define XMAGIC	0414		/*+demand load format
				 *+locations 0-1023 unmapped	   */

/*
 * Macros that take exec structures as arguments and tell whether
 * the file has a reasonable magic number or give offsets to
 * text|symbols|strings.
 */
#define N_BADMAG(x) \e
    (((x).a_magic)!=OMAGIC && ((x).a_magic)!=NMAGIC && \e
     ((x).a_magic)!=XMAGIC && ((x).a_magic)!=ZMAGIC)

#define N_TXTOFF(x) \e
	((x).a_magic>NMAGIC ? 1024 : sizeof (struct exec))
#define N_SYMOFF(x) \e
	(N_TXTOFF(x) + (x).a_text + (x).a_data \e
		     + (x).a_trsize + (x).a_drsize)
#define N_STROFF(x) \e
	(N_SYMOFF(x) + (x).a_syms)
.\}
'\"
'\"	End of nroff-only input, start of troff-only input
'\"
.if t \{\
.vS
/*
 * A.out file layout information:
 *
 * "+" indicates an addition to the Berkeley 4.1 format.
 *
 * Note:
 *	This file contains only an incomplete description of
 *	information present in an a.out file; it omits symbol
 *	table definitions.
 *
 *	Complete symbol table definitions reside in <stab.h> and
 *	simplified definitions in <nlist.h>.  These sets of
 *	definitions are not fully compatible with each other; symbol
 *	table information as defined in <nlist.h> does not correspond
 *	directly to a.out file contents, but instead is obtained by
 *	translating such information with nlist(3).
 */

/*
 * Header prepended to each a.out file.
 */
struct exec {
	 long	a_magic;	/* magic number */
unsigned long	a_text;		/* size of text segment */
unsigned long	a_data;		/* size of initialized data */
unsigned long	a_bss;		/* size of uninitialized data */
unsigned long	a_syms;		/* size of symbol table */
unsigned long	a_entry;	/* entry point address */
unsigned long	a_entry_mod;	/*+entry point - mod number */
unsigned long	a_trsize;	/* size of text relocation -
				 * specifies relocation of link
				 * tables at present */
unsigned long	a_drsize;	/* size of data relocation -
				 * current assembler sets to zero */
unsigned long	a_mod;		/*+size of mod table within text */
unsigned long	a_link;		/*+size of link table within text */
unsigned long	a_strings;	/*+size of string table */
unsigned long	a_text_addr;	/*+address of text section in
				 *+address space */
unsigned long	a_mod_addr;	/*+address of mod table in
				 *+address space */
unsigned long	a_dat_addr;	/*+address of data section in
				 *+address space */
};

#define OMAGIC	0407		/* old impure format */
#define NMAGIC	0410		/* read-only text */
#define ZMAGIC	0413		/* demand load format */
#define XMAGIC	0414		/*+demand load format
				 *+locations 0-1023 unmapped */

/*
 * Macros that take exec structures as arguments and tell whether
 * the file has a reasonable magic number or give offsets to
 * text|symbols|strings.
 */
#define N_BADMAG(x) \
    (((x).a_magic)!=OMAGIC && ((x).a_magic)!=NMAGIC && \
     ((x).a_magic)!=XMAGIC && ((x).a_magic)!=ZMAGIC)

#define N_TXTOFF(x) \
	((x).a_magic>NMAGIC ? 1024 : sizeof (struct exec))
#define N_SYMOFF(x) \
	(N_TXTOFF(x) + (x).a_text + (x).a_data \
		     + (x).a_trsize + (x).a_drsize)
#define N_STROFF(x) \
	(N_SYMOFF(x) + (x).a_syms)
.vE	\
.\}
'\"
'\"	Back to common input.
'\"
.DT
.fi
.PP
This file has five sections:
a header,
the program text and data,
relocation information,
a symbol table,
and a string table.
At present,
.IR ld (1)
ignores all relocation information.
The assembler does not provide any relocation information.
The last three sections may be omitted if the
symbols and relocation have been removed by
.IR strip (1).
.PP
In the header the sizes of each section are given in bytes.
The size of the header is not included in
any of the other sizes.
.PP
When an 
.I a.out 
file is executed,
three logical segments are set up:
the text segment,
the data segment
(with uninitialized data,
which starts off as all 0,
following initialized),
and a stack.
The text segment begins at location 0 in the core image;
the header is not loaded.
The text segment begins with the module table,
followed by the code and link tables for the modules.
Magic numbers control where the text segment begins in the
address space.
.PP
If the magic number is OMAGIC (0407),
the text segment starts at location 0 in the address space and is not to be
write-protected or shared,
so the data segment is immediately
contiguous with the text segment.
This is rarely used.
.PP 
If the magic number is NMAGIC (0410),
the data segment begins at the first 0 mod 1024 byte boundary
following the text segment,
and the program cannot write on the text segment.
Just as in the OMAGIC file,
however,
the data follows immediately after the text segment in the 
.I a.out
file.
This is the format used by the assembler.
.PP
If the magic number is ZMAGIC (0413),
the data segment begins at the first 0 mod 1024 byte boundary
following the text segment,
the size of the text segment is a whole
number of 1024 byte blocks,
and the program cannot write on text segment.
If other processes are executing the same file,
they will share the text segment.
.PP
If the magic number is XMAGIC (0414),
the first two pages of the address space are unmapped
to trap references through zero pointers,
and the text segment starts at address 0x400,
but otherwise the format is as for ZMAGIC.
.PP
For both XMAGIC and ZMAGIC format,
the text segment begins at offset 1024 in the
.I a.out
file
and the remaining bytes after the header in the first block are reserved
and should be zero.
In this case the text and data sizes must both be multiples of 1024 bytes,
and the pages of the file will be brought into the running image as needed.
This is especially suitable for very large programs and is the default
format produced by
.IR ld (1).
.PP
The stack will occupy the highest possible locations in the core image:
growing downwards from 0xfffc00.
The stack is automatically extended as required.
The data segment is only extended as requested by
.IR break (2).
.PP
After the header in the file follow the text,
data,
text relocation,
data relocation,
symbol table,
and string table in that order.
The text begins at byte 1024 in the file for XMAGIC or ZMAGIC format
or just after the header for the other formats.
The N_TXTOFF macro returns this absolute file position
when given the name of an exec structure as argument.
The data segment is contiguous with the text
and is immediately followed by the text relocation and then the data
relocation information.
The symbol table follows all this;
its position is computed by the N_SYMOFF macro.
Finally,
the string table immediately follows the symbol table
at a position that can be gotten easily using N_STROFF.
.PP
.B "Address Mapping"
.PP
Although the magic numbers specify how a file is to be mapped into
the address space,
there are also three numbers that specify this
information redundantly for files that may be executed under \*(GE.
These numbers also allow more complex mappings if the file is not
executed under \*(GE.
These numbers specify the 
starting addresses for three
different parts of the address space:
the mod table,
the code and link tables,
and the data
(both initialized and uninitialized).
Within the text section of the 
.I a.out 
file are two subsections:
the mod table and everything else.
The starting addresses of these two
sections may be specified independently to the linker.
.PP
The addresses in the 
.I a.out 
file do not match quite as well to these
sections of the file.
One address is for the starting address of the mod table.
Another address is for the starting address of the data.
The last address is the starting address of the text section
assuming that the mod table is at the beginning of the text section.
If the mod table is really elsewhere,
then nothing will actually
exist until after the mod table.
These three numbers indicate the
assumptions that were made by the linker when it created the mod
table, the link tables, and the entry point in the image.
.PP
.B "Symbol Table"
.PP
The symbol table is an array of 12-byte entries,
each of which identifies its purpose.
The symbol table contains all of the information
that is not stored within the address space,
but is needed by
.IR ld (1),
by symbolic debuggers,
or by any other programs.
The symbol table format is described in
.IR stab (5).
.SH FILES
.nf
/usr/include/a.out.h
/usr/include/stab.h
.fi
.SH "SEE ALSO"
as(1), ddt(1), ld(1), nm(1), strip(1), stab(5)
.SH CROSS-SUPPORT
In a cross-support environment,
the name of the
.I Series 32000
.I a.out 
file is 
.IR a16.out , 
while the include files are in
/usr/NSC/include/a.out.h and /usr/NSC/include/stab.h.
DataMuseum.dk

ICL Comet 32

⟦4fbb35786⟧ TextFile

Derivation

TextFile
