ld/PORTING

   1 Some incomplete notes about porting GNU ld
   2 -----------------------------------------
   3
   4 Before porting ld itself, you will need to port the BFD library.
   5
   6 We tarlk about the 'host' system as the machine and software
   7 nevironment where ld runs (generates an execuitble *on*),
   8 while the 'target' is the machine ld generates an executable *for*.
   9 Most often, host==target, but ld supports cross-linking
  10 (and to some extent the same ld binary can be used a linker
  11 for multiple target rachitectures).
  12
  13 Doing a 'host' port means working around broken or missing
  14 include files or libraries. ...
  15
  16 Porting to a new target
  17 -----------------------
  18
  19 Writing a new script script
  20 ---------------------------
  21
  22 You may need to write a new script file for your emulation.
  23
  24 The variable RELOCATING is only set if relocation is happening
  25 (i.e. unless the linker is invoked with -r).
  26 Thus your script should has an action ACTION
  27 that should only be done when relocating,
  28 express that as:
  29         ${RELOCATING+ ACTION}
  30 In general, this is the case for most assignments, which should look like:
  31         ${RELOCATING+ _end = .}
  32
  33 Also, you should assign absolute addresses to sections only
  34 when relocating, so:
  35           .text ${RELOCATING+ ${TEXT_START_ADDR}}:
  36
  37 The forms:
  38          .section { ... } > section
  39 should be:
  40          .section { ... } > ${RELOCATING+ section}
  41
  42 Old Makefile comments (re-write - FXIME!)
  43 -----------------------------------------
  44
  45 # The .xn script is used if the -n flag is given (write-protect text)..
  46 # Sunos starts the text segment for demand-paged binaries at 0x2020
  47 # and other binaries at 0x2000, since the exec header is paged in
  48 # with the text.  Some other Unix variants do the same.
  49 # For -n and -N flags the offset of the exec header must be removed.
  50 # This sed script does this if the master script contains
  51 # a line of the form ".text 0xAAAA BLOCK(0xBBBB):" - the
  52 # output will contain ".text 0xBBBB:".  (For Sunos AAAA=2020 and BBBB=2000.)
  53 .x.xn:
  54         sed -e '/text/s/\.text .* BLOCK(\([^)]*\)):/.text \1:/' < $< >$*.xn
  55
  56 # The .xN script is used if the -N flag is given (don't write-protect text).
  57 # This is like -n, except that the data segment need not be page-aligned.
  58 # So get rid of commands for page-alignment:  We assume these use ALIGN
  59 # with a hex constant that end with 00, since any normal page size is be
  60 # at least divisible by 256.  We use the 00 to avoid matching
  61 # anything that tries to align of (say) 8-byte boundaries.
  62 .xn.xN:
  63         sed -e '/ALIGN/s/ALIGN( *0x[0-9a-fA-F]*00 *)/./' < $< >$*.xN