The SGI_ABI environment variable can be used to specify whether you want an old 32-bit, high performance 32-bit (N32) or 64-bit compilation environment. It is overridden by using the -32 (or -o32), -64 or -n32 option on the command line.

Because there are three distinct ABIs used by programs with accompanying libraries, there are three distinct sets of rld search paths and three sets of environment variables.

The default library search path for o32 (old 32-bit ABI) programs is (/usr/lib:/usr/lib/internal:/lib), which can be overridden by either of the environment variables _RLD_ROOT or LD_LIBRARY_PATH.

The default library search path for 64 (64-bit ABI) programs is (/usr/lib64:/usr/lib64/internal:/lib64), which can be overridden by either of the environment variables _RLD64_ROOT or LD_LIBRARY64_PATH.

The default library search path for n32 (new 32-bit ABI) programs is (/usr/lib32:/usr/lib32/internal:/lib32), which can be overridden by either of the environment variables _RLDN32_ROOT or LD_LIBRARYN32_PATH.

For n32 or 64-bit programs, if LD_LIBRARYN32_PATH or LD_LIBRARY64_PATH is not specified, then rld will honor LD_LIBRARY_PATH if specified.

This section lists the differences between the supported switches of the 32-bit and 64-bit compilers.

If you use the -32 switch on the compiler command line, the 32-bit (ucode) compiler is invoked. If you use -64 or -n32, the 64-bit compiler is run.

The default switches on all R8000 based platforms are -64 -mips4. On all other platforms the default switches are -32 -mips2 unless the /etc/compiler.defaults file is present. If it is, its contents will specify what the default values are.

Although they are two separate and different compiler systems, the 32-bit and 64-bit compilers have similar command line interfaces. The following list summarizes the differences between the compilers in the switches that they support. A full list can be found in the cc(1), f77(1) and f90(1) man pages:

In addition to the switches listed above, both the 64-bit Fortran and 64-bit C compilers support many more switches. These switches are used to control the types of optimizations the compilers perform. This section outlines the various optimizations that the 64-bit compilers can perform, and lists the switches used to control them. To get a summary of the flags and their values set the -LIST:all_options=ON flags on the command line. For example:

%f77 -64 -O3 -mips4 -LIST:all_options=ON foo.f

This creates a .l file which contains a summary of all the flags used in the compilation including the default values of flags not explicitly set on the command line.

The optimizations and switches fall into the following categories:

Because they are two separate and different compiler systems, the 32-bit and 64-bit MIPSpro compilers have different warning and error messages.

The 32-bit C compiler emits errors as follows: the phase of the compiler which detects an error or warning, identifies itself first, then it prints whether it found an error or warning. The next printed items are the file name, line number and description of the error.

Fortran error messages are similar except the compiler phase name is omitted.

Two examples illustrate this:

C:

%cc -32 test.c

cfe: Error: test.c, line 4: Syntax Error

Fortran:

% f77 -32 err.f

Error on line 6 of err.f: syntax error

Under the 64-bit compiler, back end warning messages start with the string "!!!". Error messages start with the string "###". This allows easier searches in log files. C error messages are similar to the 32-bit compiler's error messages, although they are usually more descriptive.

Here the same files compiled with the 64-bit compiler result in the following error messages:

C:

%cat test.c

#include <stdio.h>
main ()
{
    printf ("help")

}

%cc -64 test.c
"test.c", line 4: error(1065): expected a ";"

Fortran:

%cat err.f
        program test
c
c
2       write(6,8)
8       formatr('This is a test')
        end

% f77 -64 err.f
"err.f", line 6: error(2080): expected a "("
8       formatr('This is a test')
                      ^
1 error detected in the compilation of "err.f"
Important Warning Messages

When porting a 32-bit application to 64-bits use the -fullwarn option to expose variable size related issues. Two warnings in particular emitted by the 64-bit C compiler are helpful in this respect. They allow you to locate faulty assumptions that integers and pointers are the same size.

i = (unsigned) p;

The cc driver automatically picks the correct compiler, linker, and library paths if you use the -32, -n32 or -64 switches on the command line. If you compile and link separately, you must use these switches on both the cc driver and ld command lines. If you link with libraries that are not included with IRIX or the compiler, you must make sure that they are of the proper type. Remember, you can't link 32-bit applications with N32 or 64-bit .so's.

To create your own N32, 64-bit or 32-bit libraries, you must supply the correct switch on the archiver command line.