gcc/config/i370/README

   1
   2 This directory contains code for building a compiler for the
   3 32-bit ESA/390 architecture.  It supports three different styles
   4 of assembly:
   5
   6 -- MVS for use with the HLASM assembler
   7 -- Open Edition (USS Unix System Services)
   8 -- ELF/Linux for use with the binutils/gas GNU assembler.
   9
  10
  11 Cross-compiling Hints
  12 ---------------------
  13 When building a cross-compiler on AIX, set the environment variable CC
  14 and be sure to set the -ma and -qcpluscmt flags; i.e.
  15
  16    export CC="cc -ma -qcpluscmt"
  17
  18 do this *before* running configure, e.g.
  19
  20    configure --target=i370-ibm-linux --prefix=/where/to/install/usr
  21
  22 The Objective-C and FORTRAN front ends don't build.  To avoid looking at
  23 errors, do only
  24
  25    make LANGUAGES=c
  26
  27
  28 OpenEdition Hints
  29 -----------------
  30 The shell script "install" is handy for users of OpenEdition.
  31
  32
  33 The ELF ABI
  34 -----------
  35 This compiler, in conjunction with the gas/binutils assembler, defines
  36 a defacto ELF-based ABI for the ESA/390 architecture.  Be warned: this
  37 ABI has several major faults.  It should be fixed.  As it is fixed,
  38 it is subject to change without warning.  You should not commit to major
  39 software systems without further exploring and fixing these problems.
  40 Here are some of the problems:
  41
  42 -- No support for shared libraries or dynamically loadable objects.
  43    This is because the compiler currently places address literals in
  44    the text section.  Although the GAS assembler supports a syntax for
  45    USING that will place address literals in the data section, this forces
  46    the use of two base registers, one for branches and one for the literal
  47    pool. Work is needed to redesign the function prologue, epilogue and the
  48    base register reloads to minimize the currently excessive use of reserved
  49    registers.
  50
  51    I beleive the best solution would be to add a toc or plt, and extending
  52    the meaning of the USING directive to encompass this.  This would
  53    allow the continued use of the human-readable and familiar practice
  54    of using =A() and =F'' to denote address literals, as opposed to more
  55    difficult jump-table notation.
  56
  57 -- the stackframe is almost twice as big as it needs to be.
  58
  59 -- currently, r15 is used to return 32-bit values.  Because this is the
  60    last register, it prevents 64-bit ints and small structures from being
  61    returned in registers, forcing return in memory.  It would be more
  62    efficient to use r14 to return 32-bit values, and r14+r15 to return
  63    64-bit values.
  64
  65 -- all arguments are currently passed in memory.  It would be more efficient
  66    to pass arguments in registers.
  67
  68
  69
  70
  71 ChangeLog
  72 ---------
  73 Oct98-Dec98 -- add ELF back end; work on getting ABI more or less functional.
  74 98.12.05 -- fix numerous MVC bugs
  75 99.02.06 -- multiply insn sometimes not generated when needed.
  76          -- extendsidi bugs, bad literal values printed
  77          -- remove broken adddi subdi patterns
  78 99.02.15 -- add clrstrsi pattern
  79          -- fix -O2 divide bug
  80 99.03.04 -- base & index reg usage bugs
  81 99.03.15 -- fixes for returning long longs and structs (struct value return)
  82 99.03.29 -- fix handling & alignment of shorts
  83 99.03.31 -- clobbered register 14 is not always clobbered
  84 99.04.02 -- operand constraints for cmphi
  85 99.04.07 -- function pointer fixes for call, call_value patterns,
  86             function pointers derefed once too often.
  87 99.04.14 -- add pattern to print double-wide int
  88          -- check intval<4096 for misc operands
  89          -- add clrstrsi pattern
  90          -- movstrsi fixes
  91 99.04.16 -- use r2 to pass args into r11 in subroutine call.
  92          -- fixes to movsi; some operand combinations impossible;
  93             rework constraints
  94          -- start work on forward jump optimization
  95          -- char alignment bug
  96 99.04.25 -- add untyped_call pattern so that builtin_apply works
  97 99.04.27 -- fixes to compare logical under mask
  98 99.04.28 -- reg 2 is clobbered by calls
  99 99.04.30 -- fix rare mulsi bug
 100 99.04.30 -- add constraints so that all RS, SI, SS forms insns have valid
 101             addressing modes
 102 99.04.30 -- major condition code fixes. The old code was just way off
 103             w.r.t. which insns set condition code, and the codes that
 104             were set.  The extent of this damage was unbeleivable.
 105 99.05.01 -- restructuring of operand constraints on many patterns,
 106             many lead to invalid instructions being genned.
 107 99.05.02 -- float pt fixes
 108          -- fix movdi issue bugs
 109 99.05.03 -- fix divide insn; was dividing incorrectly
 110 99.05.05 -- fix sign extension problems on andhi
 111          -- deprecate some constraints
 112 99.05.06 -- add set_attr insn lengths; fix misc litpool sizes
 113          -- add notes about how unsigned jumps work (i.e.
 114             arithmetic vs. logical vs. signed vs unsigned).
 115 99.05.11 -- use insn length to predict forward branch target;
 116             use relative branchining where possible,
 117             remove un-needed base register reload.
 118 99.05.15 -- fix movstrsi, clrstrsi, cmpstrsi patterns as per conversation
 119             w/ Richard Henderson
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