gas/NOTES.config

   1
   2                       The GAS Configuration Plan
   3
   4 Theory:
   5
   6 The goal of the new configuration scheme is to bury all object format,
   7 target processor, and host machine dependancies in object, target, and
   8 host specific files.  That is, to move all #ifdef's out of the gas
   9 common code.
  10
  11 Here's how it works.  There is a .h and a .c file for each object file
  12 format, a .h and a .c file for each target processor, and a .h for
  13 each host.  config.gas creates {sym}links in the current directory to
  14 the appropriate files in the config directory.  config.gas also serves
  15 as a list of triplets {host, target, object-format} that have been
  16 tested at one time or another.  I also recommend that config.gas be
  17 used to document triplet specific notes as to purpose of the triplet,
  18 etc.
  19
  20 Implementation:
  21
  22 host.h is a {sym}link to .../config/xm-yourhost.h.  It is intended to
  23 be used to hide host compiler, system header file, and system library
  24 differences between host machines.  If your host needs actual c source
  25 files, then either: these are generally useful functions, in which
  26 case you should probably build a local library outside of the gas
  27 source tree, or someone, perhaps me, is confused about what is needed
  28 by different hosts.
  29
  30 obj-format.h is a {sym}link to .../config/obj-something.h.  It is intended
  31
  32 All gas .c files include as.h.
  33
  34 as.h #define's "gas", includes host.h, defines a number of gas
  35 specific structures and types, and then includes tp.h, obj.h, and
  36 target-environment.h.
  37
  38 target-environment.h defines a target environment specific
  39 preprocessor flag, eg, TE_SUN, and then includes obj-format.h.
  40
  41 obj-format.h defines an object format specific preprocessor flag, eg,
  42 OBJ_AOUT, OBJ_BOUT, OBJ_COFF, includes "target-processor.h", and then
  43 defines the object specific macros, functions, types, and structures.
  44
  45 target-processor.h
  46
  47 target-processor.
  48
  49 Porting:
  50
  51 There appear to be four major types of ports; new hosts, new target
  52 processors, new object file formats, and new target environments.