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Annotation of OpenXM_contrib/gmp/doc/isa_abi_headache, Revision 1.1.1.1

1.1       maekawa     1: Terms Used In This Document:
                      2:   ISA = Instruction Set Architecture.   The instructions the current
                      3:         processor provides.
                      4:   ABI = Application Binary Interface.  Specifies calling convention,
                      5:         type sizes, etc.
                      6:   AR64 = Arithmetic operations are 64-bit using 64-bit instructions
                      7:         (E.g., addition, subtraction, load, store, of 64-bit integer types
                      8:         are done with single instructions, not 32 bits at a time.)
                      9:   Environment = The operating system and compiler.
                     10:
                     11: GMP is a very complex package to build since its speed is very
                     12: sensitive to the ISA and ABI.  For example, if the ISA provides 64-bit
                     13: instructions, it is crucial that GMP is configured to use them.
                     14:
                     15: Most environments that run on a 64-bit ISA provide more than one ABI.
                     16: Typically one of the supported ABI's is a backward compatible 32-bit
                     17: ABI, and one ABI provides 64-bit addressing and `long' (sometimes
                     18: known as LP64).  But a few environments (IRIX, HP-UX) provide
                     19: intermediate ABI's using 32-bit addressing but allow efficient 64-bit
                     20: operations through a `long long' type.  For the latter to be useful to
                     21: GMP, the ABI must allow operations using the native 64-bit
                     22: instructions provided by the ISA, and allow passing of 64-bit
                     23: quantities atomically.
                     24:
                     25: The ABI is typically chosen by means of command line options to the
                     26: compiler tools (gcc, cc, c89, nm, ar, ld, as).  Different environments
                     27: use different defaults, but as of this writing (May 2000) the
                     28: dominating default is to the plain 32-bit ABI in its most arcane form.
                     29:
                     30: The GMP 3.0.x approach was to compile using the ABI that gives the
                     31: best performance.  That places the burden on users to pass special
                     32: options to the compiler when they compile their GMP applications.
                     33: That approach has its advantages and disadvantages.  The main
                     34: advantage is that users don't unknowingly get bad GMP performance.
                     35: The main disadvantage is that users' compiles (actually links) will
                     36: fail unless they pass special compiler options.
                     37:
                     38: ** SPARC
                     39:
                     40: System vendors often confuse ABI, ISA, and implementation.  The worst
                     41: case is Solaris, were the unbundled compiler confuses ISA and ABI, and
                     42: the options have very confusing names.
                     43:
                     44:      option            interpretation
                     45:      ======            ==============
                     46: cc   -xarch=v8plus     ISA=sparcv9, ABI=V8plus (PTR=32, see below)
                     47: gcc  -mv8plus          ISA=sparcv9, ABI=V8plus (see below)
                     48: cc   -xarch=v9         ISA=sparcv9, ABI=V9 (implying AR=64, PTR=64)
                     49:
                     50: It's hard to believe, but the option v8plus really means ISA=V9!
                     51:
                     52: Solaris releases prior to version 7 running on a V9 CPU fails to
                     53: save/restore the upper 32 bits of the `i' and `l' registers.  The
                     54: `v8plus' option generates code that use as many V9 features as
                     55: possible under such circumstances.
                     56:
                     57: ** MIPS
                     58:
                     59: The IRIX 6 compilers gets things right.  They have a clear
                     60: understanding of the differences between ABI and ISA.  The option
                     61: names are descriptive.
                     62:
                     63:      option            interpretation
                     64:      ======            ==============
                     65: cc   -n32              ABI=n32 (implying AR=64, PTR=32)
                     66: gcc  -mabi=n32         ABI=n32 (implying AR=64, PTR=32)
                     67: cc   -64               ABI=64 (implying AR=64, PTR=64)
                     68: gcc  -mabi=64          ABI=64 (implying AR=64, PTR=64)
                     69: cc   -mips3            ISA=mips3
                     70: gcc  -mips3            ISA=mips3
                     71: cc   -mips4            ISA=mips4
                     72: gcc  -mips4            ISA=mips4
                     73:
                     74: ** HP-PA
                     75:
                     76: HP-UX is somewhat weird, but not as broken as Solaris.
                     77:
                     78:      option            interpretation
                     79:      ======            ==============
                     80: cc   +DA2.0            ABI=32bit (implying AR=64, PTR=32)
                     81: cc   +DD64             ABI=64bit (implying AR=64, PTR=64)
                     82:
                     83: Code performing 64-bit arithmetic in the HP-UX 32-bit is not
                     84: compatible with the 64-bit ABI; the former has a calling convention
                     85: that passes/returns 64-bit integer quantities as two 32-bit chunks.
                     86:
                     87: ** PowerPC
                     88:
                     89: While the PowerPC ABI's are capable of supporting 64-bit
                     90: registers/operations, the compilers under AIX are similar to Solaris'
                     91: cc in that they don't currently provide any 32-bit addressing with
                     92: 64-bit arithmetic.
                     93:
                     94:      option                    interpretation
                     95:      ======                    ==============
                     96: cc   -q64                      ABI=64bit (implying AR=64, PTR=64)
                     97: gcc  -maix64 -mpowerpc64       ABI=64bit (implying AR=64, PTR=64)