(gmp.info.gz) 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.
AMD64 (`x86_64')
On AMD64 systems supporting both 32-bit and 64-bit modes for
applications, the following ABI choices are available.
`ABI=64'
The 64-bit ABI uses 64-bit limbs and pointers and makes full
use of the chip architecture. This is the default.
Applications will usually not need special compiler flags,
but for reference the option is
gcc -m64
`ABI=32'
The 32-bit ABI is the usual i386 conventions. This will be
slower, and is not recommended except for inter-operating
with other code not yet 64-bit capable. Applications must be
compiled with
gcc -m32
(In GCC 2.95 and earlier there's no `-m32' option, it's the
only mode.)
HPPA 2.0 (`hppa2.0*', `hppa64')
`ABI=2.0w'
The 2.0w ABI uses 64-bit limbs and pointers and is available
on HP-UX 11 or up. Applications must be compiled with
gcc [built for 2.0w]
cc +DD64
`ABI=2.0n'
The 2.0n ABI means the 32-bit HPPA 1.0 ABI and all its normal
calling conventions, but with 64-bit instructions permitted
within functions. GMP uses a 64-bit `long long' for a limb.
This ABI is available on hppa64 GNU/Linux and on HP-UX 10 or
higher. Applications must be compiled with
gcc [built for 2.0n]
cc +DA2.0 +e
Note that current versions of GCC (eg. 3.2) don't generate
64-bit instructions for `long long' operations and so may be
slower than for 2.0w. (The GMP assembler code is the same
though.)
`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 CPU types `hppa2.0w', `hppa2.0'
and `hppa64', but for CPU type `hppa2.0n' only 2.0n or 1.0 are
considered.
Note that GCC on HP-UX has no options to choose between 2.0n and
2.0w modes, unlike HP `cc'. Instead it must be built for one or
the other ABI. GMP will detect how it was built, and skip to the
corresponding `ABI'.
IA-64 under HP-UX (`ia64*-*-hpux*', `itanium*-*-hpux*')
HP-UX supports two ABIs for IA-64. GMP performance is the same in
both.
`ABI=32'
In the 32-bit ABI, pointers, `int's and `long's are 32 bits
and GMP uses a 64 bit `long long' for a limb. Applications
can be compiled without any special flags since this ABI is
the default in both HP C and GCC, but for reference the flags
are
gcc -milp32
cc +DD32
`ABI=64'
In the 64-bit ABI, `long's and pointers are 64 bits and GMP
uses a `long' for a limb. Applications must be compiled with
gcc -mlp64
cc +DD64
On other IA-64 systems, GNU/Linux for instance, `ABI=64' is the
only choice.
MIPS under IRIX 6 (`mips*-*-irix[6789]')
IRIX 6 always has a 64-bit MIPS 3 or better CPU, and supports ABIs
o32, n32, and 64. n32 or 64 are recommended, and GMP performance
will be the same in each. The default is n32.
`ABI=o32'
The o32 ABI is 32-bit pointers and integers, and no 64-bit
operations. GMP will be slower than in n32 or 64, this
option only exists to support old compilers, eg. GCC 2.7.2.
Applications can be compiled with no special flags on an old
compiler, or on a newer compiler with
gcc -mabi=32
cc -32
`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', `powerpc620', `powerpc630', `powerpc970')
`ABI=aix64'
The AIX 64 ABI uses 64-bit limbs and pointers and is the
default on PowerPC 64 `*-*-aix*' systems. Applications must
be compiled with
gcc -maix64
xlc -q64
`ABI=mode32'
The `mode32' ABI uses a 64-bit `long long' limb but with the
chip still in 32-bit mode and using 32-bit calling
conventions. This is the default on PowerPC 64 `*-*-darwin*'
systems. No special compiler options are needed for
applications.
`ABI=32'
This is the basic 32-bit PowerPC ABI, with a 32-bit limb. No
special compiler options are needed for applications.
GMP speed is greatest in `aix64' and `mode32'. In `ABI=32' only
the 32-bit ISA is used and this doesn't make full use of a 64-bit
chip. On a suitable system we could perhaps use more of the ISA,
but there are no plans to do so.
Sparc V9 (`sparc64', `sparcv9', `ultrasparc*')
`ABI=64'
The 64-bit V9 ABI is available on the various BSD sparc64
ports, recent versions of Sparc64 GNU/Linux, and Solaris 2.7
and up (when the kernel is in 64-bit mode). GCC 3.2 or
higher, or Sun `cc' is required. On GNU/Linux, depending on
the default `gcc' mode, applications must be compiled with
gcc -m64
On Solaris applications must be compiled with
gcc -m64 -mptr64 -Wa,-xarch=v9 -mcpu=v9
cc -xarch=v9
On the BSD sparc64 systems no special options are required,
since 64-bits is the only ABI available.
`ABI=32'
For the basic 32-bit ABI, GMP still uses as much of the V9
ISA as it can. In the Sun documentation this combination is
known as "v8plus". On GNU/Linux, depending on the default
`gcc' mode, applications may need to be compiled with
gcc -m32
On Solaris, no special compiler options are required for
applications, though using something like the following is
recommended. (`gcc' 2.8 and earlier only support `-mv8'
though.)
gcc -mv8plus
cc -xarch=v8plus
GMP speed is greatest in `ABI=64', so it's the default where
available. The speed is partly because there are extra registers
available and partly because 64-bits is considered the more
important case and has therefore had better code written for it.
Don't be confused by the names of the `-m' and `-x' compiler
options, they're called `arch' but effectively control both ABI
and ISA.
On Solaris 2.6 and earlier, only `ABI=32' is available since the
kernel doesn't save all registers.
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
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