gas/README.rich

   1
   2
   3                  The Code Pedigree of This Directory
   4
   5
   6 This directory contains a big merge of several development lines of
   7 gas as well as a few bug fixes and some configuration that I've added
   8 in order to retain my own sanity.
   9
  10 A little history.
  11
  12 The only common baseline of all versions was gas-1.31.
  13
  14 From 1.31, Intel branched off and added:
  15
  16         support for the Intel 80960 (i960) processor.
  17         support for b.out object files.
  18         some bug fixes.
  19         sloppy mac MPW support
  20         Intel gnu/960 makefiles and version numbering.
  21
  22 Many of the bug fixes found their way into the main development line
  23 prior to 1.36.  ALL intel changes were ifdef'd I80960.  This was good
  24 as it isolated the changes, but bad in that it connected the b.out
  25 support to the i960 support, and bad in that the bug fixes were only
  26 active in the i960+b.out executables of gas, (although most of these
  27 were nicely marked with comments indicating that they were probably
  28 general bug fixes.)
  29
  30 To pick up the main FSF development line again, along the way to 1.36,
  31 several new processors were added, many bugs fixed, and the world was
  32 a somewhat better place in general.
  33
  34 From gas-1.36, Loic at Axis Design (france!) encapsulated object
  35 format specific actions, added coff versions of those encapsulations,
  36 and a config.gas style configuration and Makefile.  This was a big
  37 change and a lot of work.
  38
  39 Then along came the FIRST FSF release of gas-1.37.  I say this because
  40 there have been at least two releases of gas-1.37.  Only two of them
  41 do we care about for this story, so let's call them gas-1.37.1 and
  42 gas-1.37.2.
  43
  44 Here starts the confusion.  Firstly, gas-1.37.1 did not compile.
  45
  46 In the meantime, John Gilmore at Cygnus Support had been hacking
  47 gas-1.37.1.  He got it to compile.  He added support for the AMD 29000
  48 processor.  AND he started encapsulating some of the a.out specific
  49 pieces of code mostly into functions.  AND he rebuilt the relocation
  50 info to be generic.  AND he restructured somewhat so that for a single
  51 host, cross assemblers could be built for all targets in the same
  52 directory.  Useful work but a considerable nuisance because the a29k
  53 changes were not partitioned from the encapsulation changes, the
  54 encapsulation changes were incomplete, and the encapsulation required
  55 functions where alternate structuring might have used macros. Let's
  56 call this version gas-1.37.1+a29k.
  57
  58 By the time gas-1.37.2 was "released", (remember that it TOO was
  59 labelled by FSF as gas-1.37), it compiled, but it also added i860
  60 support and ansi style const declarations.
  61
  62 At this point, Loic rolled his changes into gas-1.37.2.
  63
  64 What I've done.
  65
  66 I collected all the stray versions of gas that sounded relevant to my
  67 goals of cross assembly and alternate object file formats and the FSF
  68 releases from which the stray versions had branched.
  69
  70 I rolled the Intel i960 changes from 1.31 into versions that I call
  71 1.34+i960, 1.36+i960, and then 1.37.1+i960.
  72
  73 Then I merged 1.37.1+i960 with 1.37.1+a29k to produce what I call
  74 1.37.1+i960+a29k or 1.37.3.
  75
  76 From 1.37.3, I pulled in Loic's stuff.  This wasn't easy as Loic's
  77 stuff hit all the same points as John's encapsulations.  Loic's goal
  78 was to split the a.out from coff dependancies for native assembly on
  79 coff, while John's was to split for multiple cross assembly from a
  80 single host.
  81
  82 Loic's config arranged files much like emacs into m-*, etc.  I've
  83 rearranged these somewhat.
  84
  85 Theory:
  86
  87 The goal of the new configuration scheme is to bury all object format,
  88 target processor, and host machine dependancies in object, target, and
  89 host specific files.  That is, to move all #ifdef's out of the gas
  90 common code.
  91
  92 Here's how it works.  There is a .h and a .c file for each object file
  93 format, a .h and a .c file for each target processor, and a .h for
  94 each host.  config.gas creates {sym}links in the current directory to
  95 the appropriate files in the config directory.  config.gas also serves
  96 as a list of triplets {host, target, object-format} that have been
  97 tested at one time or another.  I also recommend that config.gas be
  98 used to document triplet specific notes as to purpose of the triplet,
  99 etc.
 100
 101 Implementation:
 102
 103 host.h is a {sym}link to .../config/xm-yourhost.h.  It is intended to
 104 be used to hide host compiler, system header file, and system library
 105 differences between host machines.  If your host needs actual c source
 106 files, then either: these are generally useful functions, in which
 107 case you should probably build a local library outside of the gas
 108 source tree, or someone, perhaps me, is confused about what is needed
 109 by different hosts.
 110
 111 obj-format.h is a {sym}link to .../config/obj-something.h.  It is intended
 112
 113 All gas .c files include as.h.
 114
 115 as.h #define's "gas", includes host.h, defines a number of gas
 116 specific structures and types, and then includes tp.h, obj.h, and
 117 target-environment.h.
 118
 119 target-environment.h defines a target environment specific
 120 preprocessor flag, eg, TE_SUN, and then includes obj-format.h.
 121
 122 obj-format.h defines an object format specific preprocessor flag, eg,
 123 OBJ_AOUT, OBJ_BOUT, OBJ_COFF, includes "target-processor.h", and then
 124 defines the object specific macros, functions, types, and structures.
 125
 126 target-processor.h
 127
 128 target-processor.
 129
 130 Porting:
 131
 132 There appear to be four major types of ports; new hosts, new target
 133 processors, new object file formats, and new target environments.
 134
 135
 136 -----
 137
 138 reloc now stored internally as generic. (symbols too?) (segment types
 139 vs. names?)
 140
 141 I don't mean to overlook anyone here.  There have also been several
 142 other development lines here that I looked at and elected to bypass.
 143 Specifically, xxx's stabs in coff stuff was particularly tempting.