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1.1.1.2 ! ohara       1: Copyright 2000 Free Software Foundation, Inc.
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        !             3: This file is part of the GNU MP Library.
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        !             5: The GNU MP Library is free software; you can redistribute it and/or modify
        !             6: it under the terms of the GNU Lesser General Public License as published by
        !             7: the Free Software Foundation; either version 2.1 of the License, or (at your
        !             8: option) any later version.
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        !            10: The GNU MP Library is distributed in the hope that it will be useful, but
        !            11: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            12: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            13: License for more details.
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        !            15: You should have received a copy of the GNU Lesser General Public License
        !            16: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            17: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
        !            18: 02111-1307, USA.
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1.1       maekawa    23: Terms Used In This Document:
                     24:   ISA = Instruction Set Architecture.   The instructions the current
                     25:         processor provides.
                     26:   ABI = Application Binary Interface.  Specifies calling convention,
                     27:         type sizes, etc.
                     28:   AR64 = Arithmetic operations are 64-bit using 64-bit instructions
                     29:         (E.g., addition, subtraction, load, store, of 64-bit integer types
                     30:         are done with single instructions, not 32 bits at a time.)
                     31:   Environment = The operating system and compiler.
                     32:
                     33: GMP is a very complex package to build since its speed is very
                     34: sensitive to the ISA and ABI.  For example, if the ISA provides 64-bit
                     35: instructions, it is crucial that GMP is configured to use them.
                     36:
                     37: Most environments that run on a 64-bit ISA provide more than one ABI.
                     38: Typically one of the supported ABI's is a backward compatible 32-bit
                     39: ABI, and one ABI provides 64-bit addressing and `long' (sometimes
                     40: known as LP64).  But a few environments (IRIX, HP-UX) provide
                     41: intermediate ABI's using 32-bit addressing but allow efficient 64-bit
                     42: operations through a `long long' type.  For the latter to be useful to
                     43: GMP, the ABI must allow operations using the native 64-bit
                     44: instructions provided by the ISA, and allow passing of 64-bit
                     45: quantities atomically.
                     46:
                     47: The ABI is typically chosen by means of command line options to the
                     48: compiler tools (gcc, cc, c89, nm, ar, ld, as).  Different environments
                     49: use different defaults, but as of this writing (May 2000) the
                     50: dominating default is to the plain 32-bit ABI in its most arcane form.
                     51:
                     52: The GMP 3.0.x approach was to compile using the ABI that gives the
                     53: best performance.  That places the burden on users to pass special
                     54: options to the compiler when they compile their GMP applications.
                     55: That approach has its advantages and disadvantages.  The main
                     56: advantage is that users don't unknowingly get bad GMP performance.
                     57: The main disadvantage is that users' compiles (actually links) will
                     58: fail unless they pass special compiler options.
                     59:
                     60: ** SPARC
                     61:
                     62: System vendors often confuse ABI, ISA, and implementation.  The worst
                     63: case is Solaris, were the unbundled compiler confuses ISA and ABI, and
                     64: the options have very confusing names.
                     65:
                     66:      option            interpretation
                     67:      ======            ==============
                     68: cc   -xarch=v8plus     ISA=sparcv9, ABI=V8plus (PTR=32, see below)
                     69: gcc  -mv8plus          ISA=sparcv9, ABI=V8plus (see below)
                     70: cc   -xarch=v9         ISA=sparcv9, ABI=V9 (implying AR=64, PTR=64)
                     71:
                     72: It's hard to believe, but the option v8plus really means ISA=V9!
                     73:
                     74: Solaris releases prior to version 7 running on a V9 CPU fails to
                     75: save/restore the upper 32 bits of the `i' and `l' registers.  The
                     76: `v8plus' option generates code that use as many V9 features as
                     77: possible under such circumstances.
                     78:
                     79: ** MIPS
                     80:
                     81: The IRIX 6 compilers gets things right.  They have a clear
                     82: understanding of the differences between ABI and ISA.  The option
                     83: names are descriptive.
                     84:
                     85:      option            interpretation
                     86:      ======            ==============
                     87: cc   -n32              ABI=n32 (implying AR=64, PTR=32)
                     88: gcc  -mabi=n32         ABI=n32 (implying AR=64, PTR=32)
                     89: cc   -64               ABI=64 (implying AR=64, PTR=64)
                     90: gcc  -mabi=64          ABI=64 (implying AR=64, PTR=64)
                     91: cc   -mips3            ISA=mips3
                     92: gcc  -mips3            ISA=mips3
                     93: cc   -mips4            ISA=mips4
                     94: gcc  -mips4            ISA=mips4
                     95:
                     96: ** HP-PA
                     97:
                     98: HP-UX is somewhat weird, but not as broken as Solaris.
                     99:
                    100:      option            interpretation
                    101:      ======            ==============
                    102: cc   +DA2.0            ABI=32bit (implying AR=64, PTR=32)
                    103: cc   +DD64             ABI=64bit (implying AR=64, PTR=64)
                    104:
                    105: Code performing 64-bit arithmetic in the HP-UX 32-bit is not
                    106: compatible with the 64-bit ABI; the former has a calling convention
                    107: that passes/returns 64-bit integer quantities as two 32-bit chunks.
                    108:
                    109: ** PowerPC
                    110:
                    111: While the PowerPC ABI's are capable of supporting 64-bit
                    112: registers/operations, the compilers under AIX are similar to Solaris'
                    113: cc in that they don't currently provide any 32-bit addressing with
                    114: 64-bit arithmetic.
                    115:
                    116:      option                    interpretation
                    117:      ======                    ==============
                    118: cc   -q64                      ABI=64bit (implying AR=64, PTR=64)
                    119: gcc  -maix64 -mpowerpc64       ABI=64bit (implying AR=64, PTR=64)