gcc 64bit compilation on Solaris 10

By default, if you were to build a shared library with gcc, you'd enter commands similar to

# gcc -fPIC -c file.c
# gcc -shared -o file.so file.o

The resultant shared library would be 32 bit, i.e.
# file file.so
file.so: ELF 32-bit MSB dynamic lib SPARC Version 1, dynamically linked, not stripped, no debugging information available
#

If you wish to build a 64 bit library you should amend the command above as follows:

# gcc -fPIC -m64 -mcpu=ultrasparc -c file.c
# gcc -shared -m64 -mcpu=ultrasparc -o file.so file.o

With the result:
# file file.so
file.so: ELF 64-bit MSB dynamic lib SPARCV9 Version 1, UltraSPARC1 Extensions Required, dynamically linked, not stripped, no debugging information available
#