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(gmp.info)ABI and ISA

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ABI and ISA
===========

   ABI (Application Binary Interface) refers to the calling conventions
between functions, meaning what registers are used and what sizes the
various C data types are.  ISA (Instruction Set Architecture) refers to
the instructions and registers a CPU has available.

   Some 64-bit ISA CPUs have both a 64-bit ABI and a 32-bit ABI
defined, the latter for compatibility with older CPUs in the family.
GMP supports some CPUs like this in both ABIs.  In fact within GMP
`ABI' means a combination of chip ABI, plus how GMP chooses to use it.
For example in some 32-bit ABIs, GMP may support a limb as either a
32-bit `long' or a 64-bit `long long'.

   By default GMP chooses the best ABI available for a given system,
and this generally gives significantly greater speed.  But an ABI can
be chosen explicitly to make GMP compatible with other libraries, or
particular application requirements.  For example,

     ./configure ABI=32

   In all cases it's vital that all object code used in a given program
is compiled for the same ABI.

   Usually a limb is implemented as a `long'.  When a `long long' limb
is used this is encoded in the generated `gmp.h'.  This is convenient
for applications, but it does mean that `gmp.h' will vary, and can't be
just copied around.  `gmp.h' remains compiler independent though, since
all compilers for a particular ABI will be expected to use the same
limb type.

   Currently no attempt is made to follow whatever conventions a system
has for installing library or header files built for a particular ABI.
This will probably only matter when installing multiple builds of GMP,
and it might be as simple as configuring with a special `libdir', or it
might require more than that.  Note that builds for different ABIs need
to done separately, with a fresh `./configure' and `make' each.


HPPA 2.0 (`hppa2.0*')

    `ABI=2.0w'
          The 2.0w ABI uses 64-bit limbs and pointers and is available
          on HP-UX 11 or up when using `cc'.  `gcc' support for this is
          in progress.  Applications must be compiled with

               cc  +DD64

    `ABI=2.0n'
          The 2.0n ABI means the 32-bit HPPA 1.0 ABI but with a 64-bit
          limb using `long long'.  This is available on HP-UX 10 or up
          when using `cc'.  No `gcc' support is planned for this.
          Applications must be compiled with

               cc  +DA2.0 +e

    `ABI=1.0'
          HPPA 2.0 CPUs can run all HPPA 1.0 and 1.1 code in the 32-bit
          HPPA 1.0 ABI.  No special compiler options are needed for
          applications.

     All three ABIs are available for CPUs `hppa2.0w' and `hppa2.0', but
     for CPU `hppa2.0n' only 2.0n or 1.0 are allowed.


MIPS under IRIX 6 (`mips*-*-irix[6789]')
     IRIX 6 supports the n32 and 64 ABIs and always has a 64-bit MIPS 3
     or better CPU.  In both these ABIs GMP uses a 64-bit limb.  A new
     enough `gcc' is required (2.95 for instance).

    `ABI=n32'
          The n32 ABI is 32-bit pointers and integers, but with a
          64-bit limb using a `long long'.  Applications must be
          compiled with

               gcc  -mabi=n32
               cc   -n32

    `ABI=64'
          The 64-bit ABI is 64-bit pointers and integers.  Applications
          must be compiled with

               gcc  -mabi=64
               cc   -64

     Note that MIPS GNU/Linux, as of kernel version 2.2, doesn't have
     the necessary support for n32 or 64 and so only gets a 32-bit limb
     and the MIPS 2 code.


PowerPC 64 (`powerpc64*')

    `ABI=aix64'
          The AIX 64 ABI uses 64-bit limbs and pointers and is
          available on systems `powerpc64*-*-aix*'.  Applications must
          be compiled (and linked) with

               gcc  -maix64
               xlc  -q64

    `ABI=32L'
          This uses the 32-bit ABI but a 64-bit limb using GCC `long
          long' in 64-bit registers.  Applications must be compiled with

               gcc  -mpowerpc64

    `ABI=32'
          This is the basic 32-bit PowerPC ABI.  No special compiler
          options are needed for applications.


Sparc V9 (`sparcv9' and `ultrasparc*')

    `ABI=64'
          The 64-bit V9 ABI is available on Solaris 2.7 and up and
          GNU/Linux.  GCC 2.95 or up, or Sun `cc' is required.
          Applications must be compiled with

               gcc  -m64 -mptr64 -Wa,-xarch=v9 -mcpu=v9
               cc   -xarch=v9

    `ABI=32'
          On Solaris 2.6 and earlier, and on Solaris 2.7 with the
          kernel in 32-bit mode, only the plain V8 32-bit ABI can be
          used, since the kernel doesn't save all registers.  GMP still
          uses as much of the V9 ISA as it can in these circumstances.
          No special compiler options are required for applications,
          though using something like the following requesting V9 code
          within the V8 ABI is recommended.

               gcc  -mv8plus
               cc   -xarch=v8plus

          `gcc' 2.8 and earlier only supports `-mv8' though.

     Don't be confused by the names of these sparc `-m' and `-x'
     options, they're called `arch' but they effectively control the
     ABI.

     On Solaris 2.7 with the kernel in 32-bit-mode, a normal native
     build will reject `ABI=64' because the resulting executables won't
     run.  `ABI=64' can still be built if desired by making it look
     like a cross-compile, for example

          ./configure --build=none --host=sparcv9-sun-solaris2.7 ABI=64