-xcode=v (Sun WorkShop Compiler C 5.0 User's Guide)

Sun WorkShop Compiler C 5.0 User's Guide

`-xcode=v`

(SPARC) Specify code address space. v must be one of:

abs32	Generate 32-bit absolute addresses. Code + data + bss size is limited to 2**32 bytes. This is the default on 32-bit architectures: `-xarch-generic, v7, v8, v8a, v8plus, v8plusa`
abs44	Generate 44-bit absolute addresses. Code + data + bss size is limited to 2**44 bytes. Available only on 64-bit architectures: `-xarch=v9, v9a`
abs64	Generate 64-bit absolute addresses. Available only on 64-bit architectures: `-xarch=v9, v9a`
pic13	Generate position-independent code for use in shared libraries (small model). Equivalent to -Kpic. Permits references to at most 211 unique external symbols on 32-bit architectures, 210 on 64-bit architectures. The `-xcode=pic13` command is similar to `-xcode=pic32`, except that the size of the global offset table is limited to 8Kbytes.
pic32	Generate position-independent code for use in shared libraries (large model). Equivalent to -KPIC. Permits references to at most 230 unique external symbols on 32-bit architectures, 229 on 64-bit architectures. Each reference to a global datum is generated as a dereference of a pointer in the global offset table. Each function call is generated in `pc`-relative addressing mode through a procedure linkage table. With this option, the global offset table spans the range of 32-bit addresses in those rare cases where there are too many global data objects for `-xcode=pic32`.

The default is -xcode=abs32 for SPARC V7 and V8, and -xcode=abs64 for SPARC and UltraSPARC V9 (with -xarch=v9|v9a).

When building shared dynamic libraries with -xarch=v9 or v9a on 64-bit Solaris 7, you must specify -xcode=pic13 or -xcode=pic32.

There are two nominal performance costs with -xcode=pic13 and -xcode=pic32:

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.