UM0144 datasheet(39/92 Pages) STMICROELECTRONICS

39 / 92 page

ST7 Assembler Linker

4 Linker

UM0144

39/92

each routine. Put another way, each link must have entry fixed points to all its routine, otherwise re-linking

one 'lump' of a program could make references to its addresses in other modules out of date.

4.5

The linker in more detail

4.5.1

The composition of the .OBJ files

The .OBJ files produced by the assembler contain an enormous amount of overhead, mostly as coded

expressions describing exactly what needs to go into the 'blank spaces' the assembler has been so liberal

with. The linker contains a full arithmetic parser for 'working out' complex expressions that include external

labels: This means (unlike most other assemblers) there are few restrictions on where external labels may

appear.

The assembler also includes line-number information with the .OBJ file, connecting each piece of

generated object code with a line number from a given source file.

OBJ

files also contain 'special' markers for handling SKIP and DATE type directive.

4.5.2

The composition of the .COD files

.COD

files, on the other hand, contain very little overhead; there are six bytes per segment that describe

the start address and length of that segment. Besides that, the rest of the code is in its final form. A

segment of zero length marks the end of the file. It only remains for OBSEND to take the code segment by

segment and send it on to its destination.

4.5.3

Reading a mapfile listing

The linker also generates files with the suffix .SYM and .MAP in addition to the .COD file we have already

discussed. The .SYM file contains a compact symbol table list suitable with the debuggers and simulators.

The .MAP file listing shows three important things: a table of segments with their absolute address, a table

of all classes in the program, and a list of all external labels with their true values, modules they were

defined in and size.

Here is an example MAPFILE, where one of the class, ROM, has gone past its limit, overwriting (or more

correctly, having part of itself overwritten by) VECTORS.

The [void] on some segments in the segment list says that these segments were not used to create

object code, but were used for non-coding-creating tasks such as allocating label values with ds.b etc.

The number in straight brackets on the segment as true address list shows how many segments 'into' the

module this segment is, i.e., the 1st, 2nd etc. of the given module. The first x-y shows the range of

addresses. The def (line) field on the external labels list shows the source code file and line number

that his label was defined in. The number at the start of each class list line is the cod-file that the class

contents were sent to (default is 0).

UM0144 Datasheet(PDF) 39 Page - STMicroelectronics

UM0144 Datasheet(HTML) 39 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

Datasheet Download

Link URL