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ABI(5)
NAME
ABI - Application Binary Interface
DESCRIPTION
This man page is a quick reference for the three Application Binary
Interfaces (ABI) that are supported by IRIX.
GENERAL INFORMATION
An ABI defines a system interface for executing compiled programs. It
defines which Instruction Set Architectures (ISA) it supports as well
as defining object file formats and calling conventions.
IRIX supports three ABIs:
o32 The old 32-bit ABI which was standard on IRIX 5 systems.
n64 The 64-bit ABI which was introduced on IRIX 6.0 systems.
n32 The new high performance 32-bit ABI which was introduced on IRIX
6.2.
Each of these ABIs defines unique interfaces which make it impossible
to link object files of one ABI with object files of another ABI.
The MIPS ABI is a subset of the above mentioned o32 ABI and is
designed to provide application portability across a variety of vendor
platforms.
Default ABI and ISA settings described in this man page can be
overridden by changing the default settings for a given system,
contained in the /etc/compiler.defaults file; or by changing the
SGI_ABI environment variable, which can be used to specify default ABI
values.
o32 Information
The o32 ABI supports the mips2 ISA (by default) and mips1 ISA. The
resulting program binary is in ELF32 format (COFF is no longer
supported) whose symbol table is in .mdebug format. The o32 calling
convention allows a maximum of four registers ($a0..$a3) to be used to
pass integer arguments.
When an o32 program executes, IRIX sets the FR bit in the status
register of the MIPS microprocessor to 0. Under this setting, only 16
double precision floating point registers are enabled.
C language integer types (int), long integer types (long), and pointer
types (char *) are all 32-bits wide in programs compiled for this ABI.
A program is compiled for the o32 ABI under the following
circumstances:
* By default on systems that are not based on the R8000 (if the
environment variable SGI_ABI is not set), as in this example:
cc foo.c
* By using the -32 compilation flag; this overrides any SGI_ABI
setting, as in this example:
cc -32 foo.c
* By using the -mips2 or -mips1 compilation flags, as in this example:
cc -mips2 foo.c
* By setting the SGI_ABI environment variable to -32 and doing a
default compilation, as in this example:
setenv SGI_ABI -32
cc foo.c
* By setting the default ABI to -32 in the /etc/compiler.defaults
file, as in this example:
cat /etc/compiler.defaults
-DEFAULT:abi=o32
An o32 compilation generates certain predefined variables whose values
can be used by conditional compilation directives. The names of these
variables and their values are as follows:
_MIPS_FPSET = 16
_MIPS_ISA = 2
_ABIO32 = 1
_MIPS_SIM = _ABIO32
_MIPS_SZINT = 32
_MIPS_SZLONG = 32
_MIPS_SZPTR = 32
For more information about these predefined variables, see the
<sgidefs.h> include file.
n64 Information
The n64 ABI supports the mips4 ISA (by default) and mips3 ISA. The
resulting program binary is in ELF64 format whose symbol table is in
DWARF format. The n64 calling convention is different from the o32
calling convention in that it allows a maximum of eight registers
($a0..$a7) to be used to pass integer arguments. It also allows a
maximum of eight floating point registers to be used to pass floating
point arguments. A full description of this calling convention can be
found in the MIPSpro 64-Bit Porting and Transition Guide.
When an n64 program executes, IRIX sets the FR bit in the status
register of the MIPS microprocessor to 1. Under this setting, all 32
double precision floating point registers are enabled. This improves
performance, but old assembly code that accesses a double precision
floating point register as a pair (one even and one odd) of single
precision floating point registers will not work.
C language integer types (int) are 32 bits wide, while long integer
types (long), and pointer types (char *) are both 64-bits wide in
programs compiled for this ABI.
A program is compiled for the n64 ABI under the following
circumstances:
* By default on systems that are based on the R8000 (if the
environment variable SGI_ABI is not set), as in this example:
cc foo.c
* By using the -64 compilation flag; this overrides any SGI_ABI
setting, as in this example:
cc -64 foo.c
* By using the -mips4 or -mips3 compilation flags, as in this example:
cc -mips4 foo.c
* By setting the SGI_ABI environment variable to -64 and doing a
default compilation, as in this example:
setenv SGI_ABI -64
cc foo.c
* By setting the default ABI to -64 in the /etc/compiler.defaults
file, as in this example:
cat /etc/compiler.defaults
-DEFAULT:abi=64
An n64 compilation generates certain predefined variables whose values
can be used by conditional compilation directives. The names of these
variables and their values are as follows:
_MIPS_FPSET = 32
_MIPS_ISA = 4
_ABI64 = 3
_MIPS_SIM = _ABI64
_MIPS_SZINT = 32
_MIPS_SZLONG = 64
_MIPS_SZPTR = 64
n32 Information
The n32 ABI supports the mips3 (by default) and mips4 ISA. The
resulting program binary is in ELF32 format whose symbol table is in
DWARF format. The n32 calling convention is the same as the n64
calling convention. A full description of this calling convention can
be found in the MIPSpro N32 ABI Handbook.
When an n32 program executes, IRIX sets the FR bit in the status
register of the MIPS microprocessor to 1, just as it does for an n64
program. Under this setting, all 32 double precision floating point
registers are enabled. This has the same performance and
compatibility implications as with n64.
C language integer types (int), long integer types (long), and pointer
types (char *) are all 32-bits wide in programs compiled for this ABI.
A program is compiled for the n32 ABI under the following
circumstances:
* By using the -n32 compilation flag; this overrides any SGI_ABI
setting, as in this example:
cc -n32 foo.c
* By setting the SGI_ABI environment variable to -n32 and doing a
default compilation, as in this example:
setenv SGI_ABI -n32
cc foo.c
* By setting the default ABI to -n32 in the /etc/compiler.defaults
file.
cat /etc/compiler.defaults
-DEFAULT:abi=n32
An N32 compilation will generate certain predefined variables whose
values can be used by conditional compilation directives. The names
of these variables and their values are as follows:
_MIPS_FPSET = 32
_MIPS_ISA = 3
_ABI64 = 3
_MIPS_SIM = _NABI32
_MIPS_SZINT = 32
_MIPS_SZLONG = 32
_MIPS_SZPTR = 32
_ABIN32 = 2
_MIPS_SIM = _ABIN32
Summary Table
The table below summarizes the characteristics of the three ABI's.
-----------------------------------------------------------------
Category O32 n64 n32
-----------------------------------------------------------------
Command Line Switch -32 -64 -n32
Supported ISA mips1,2 mips 3,4 mips 3,4
Default ISA mips2 mips4 mips3
Object file format ELF32 ELF64 ELF32
Debug info format mdebug DWARF DWARF
Symbol table format ELF32 ELF64 ELF32
Number of double 16 32 32
precision floating
point registers
bits in int 32 32 32
bits in long 32 64 32
bits in char * 32 64 32
-----------------------------------------------------------------
SEE ALSO
The MIPSpro N32 ABI Handbook and the MIPSpro 64-Bit Porting and
Transition Guide provide information about the calling convention as
well as background on these ABIs.
mips_ext(5)
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