Defaults

The default is -xcode=abs32 for 32–bit architectures. The default for 64–bit architectures is-xcode=abs44.

When building shared dynamic libraries, the default -xcode values of abs44 and abs32 will not work with 64–bit architectures. Specify -xcode=pic13 or -xcode=pic32 instead. There are two nominal performance costs with -xcode=pic13 and -xcode=pic32 on SPARC:

• A routine compiled with either -xcode=pic13 or -xcode=pic32 executes a few extra instructions upon entry to set a register to point at a table (_GLOBAL_OFFSET_TABLE_) used for accessing a shared library’s global or static variables.

• Each access to a global or static variable involves an extra indirect memory reference through _GLOBAL_OFFSET_TABLE_. If the compile is done with -xcode=pic32, there are two additional instructions per global and static memory reference.

When considering the above costs, remember that the use of -xcode=pic13 and -xcode=pic32 can significantly reduce system memory requirements, due to the effect of library code sharing. Every page of code in a shared library compiled -xcode=pic13 or– xcode=pic32 can be shared by every process that uses the library. If a page of code in a shared library contains even a single non-pic (that is, absolute) memory reference, the page becomes nonsharable, and a copy of the page must be created each time a program using the library is executed.

The easiest way to tell whether or not a .o file has been compiled with -xcode=pic13 or –xcode=pic32 is with the nm command:

% nm file.o | grep _GLOBAL_OFFSET_TABLE_ U _GLOBAL_OFFSET_TABLE_

A .o file containing position-independent code contains an unresolved external reference to _GLOBAL_OFFSET_TABLE_, as indicated by the letter U.

To determine whether to use -xcode=pic13 or -xcode=pic32, use nm to identify the number of distinct global and static variables used or defined in the library. If the size of _GLOBAL_OFFSET_TABLE_ is under 8,192 bytes, you can use -Kpic. Otherwise, you must use -xcode=pic32.