.so macro
.he 'C.OUT''C.OUT'
.n NAME c.out
c.out - 68000 loader output
.d DESCRIPTION
'c.out' is the output file of the loader 'ld68 (cmnd)'.
The loader makes 'c.out' executable if there were no
errors and no unresolved external references.
The *.o relocatable object files which are produced by the assembler
'as68 (cmnd)' have this same format.
.sp
This file has four sections:
a header, the program and data text, a symbol table, and relocation bits
(in that order).
The last two may be empty if the program was loaded
with the '-s' option of 'ld68 (cmnd)'.
.sp
There are two formats of the header.
The first header format starts
with the identifying number 601A hex and contains 14 words in the
following format:
.sp
.nf
.na
.in +5
struct hdr {
    int magic;         //c.out magic number = 601A hex
    long tsize;        //# bytes in program text segment
    long dsize;        //# bytes in program data segment
    long bsize;        //# bytes in program bss  segment
    long ssize;        //# bytes in symbol table
    long stksize;      //initial stack size
    long entry;        //entry point
    int rlbflg;        //relocation bits suppressed flag
 };
.fi
.ad
.sp
.in -5
The second header format is used when noncontiguous text, data,
and bss segments are specified to the loader using the -T, -D,
and -B flags.
This header begins with the identifying number
601B hex and contains 18 words in the following format:
.sp
.in +5
.nf
.na
struct hdr {
    int magic;         //c.out magic number = 601B hex
    long tsize;        //# bytes in program text segment
    long dsize;        //# bytes in program data segment
    long bsize;        //# bytes in program bss  segment
    long ssize;        //# bytes in symbol table
    long stksize;      //initial stack size
    long entry;        //entry point--address of text segment
    int rlbflg;        //relocation bits suppressed flag
    long dstart;       //address of data segment
    long bstart;       //address of bss segment
 };
.fi
.ad
.sp
.in -5
The sizes of each segment are in bytes but are even.
The size of the header is not included in any of the other sizes.
.sp
When a file produced by the loader is loaded into memory for execution,
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 the address contained in "entry"
in the core image; the header is not loaded.
If the magic number (word 0) is 601A hex, it indicates that the text
segment is not to be write-protected and shared,
so the data segment is immediately contiguous
with the text segment.
If the magic number is 601C hex, it indicates that the text segment is
to be write protected and shared and that the beginning of the data
segment is at the first 2K byte boundary beyond the text segment.
If the magic number is 601D hex, it indicates that the text segment and
the data segment are both loaded with virtual addresses beginning
at 0 (I and D split).
If the magic number is 601E hex, it indicates that the text segment is
to be write protected and shared and that the beginning of the data
segment is at the first 4K byte boundary beyond the text segment.
.sp
The symbol table consists of 7-word entries.
The first four words contain the ASCII name of the symbol, null-padded.
The next word is a flag indicating the type of symbol.
The following values are possible:
.sp
.in +5
.nf
.na
0100000        defined
0040000        equated
0020000        global - entry or external
0010000        equated register
0004000        external reference
0002000        DATA based relocatable
0001000        TEXT based relocatable
0000400        BSS based relocatable
.in -5
.fi
.ad
.sp
These values are bit flags which may be or'ed together to indicate
completely a symbol type such as 0122000 for a defined global data
segment relocatable symbol.
.sp
The last two words (long) of a symbol table
entry contain the value of the symbol.
.sp
If the symbol's type is undefined external,
and the value field is non-zero,
the symbol is interpreted by the loader
ld
as the name of a common region
whose size is indicated by the value of the symbol.
.sp
The value of a word in the text or data portions which is not
a reference to an undefined external symbol
is exactly that value which will appear in memory
when the file is executed.
If a word in the text or data portion
involves a reference to an undefined external symbol,
as indicated by the relocation bits for that word,
then the value of the word as stored in the file
is an offset from the associated external symbol.
When the file is processed by the
loader and the external symbol becomes
defined, the value of the symbol will
be added into the word in the file.
.sp
If relocation information is present, it amounts to one word per
word of program text or initialized data.
There is no relocation information if the "suppress relocation"
flag in the header is on.
.sp
Bits 2-0 of a relocation word indicate the segment referred
to by the text or data word associated with the relocation word:
.sp
.nf
.na
.in +5
00    indicates the reference is absolute
01    indicates the reference is data segment relocatable
02    indicates the reference is text segment relocatable
03    indicates the reference is bss segment relocatable
04    indicates the reference is to an undefined external symbol
05    indicates the reference is to the upper word of a long
07    indicates the absolute first word of an instruction
.fi
.ad
.in -5
.sp
The remainder of the relocation word (bits 15-3)
contains a symbol number in the case of external
references, and is unused otherwise.
The first symbol is numbered 0, the second 1, etc.
.sa "SEE ALSO"
as68 (cmnd), ld68 (cmnd)
