Symbol Addresses

The architecture of a Alpha processor affects local variable symbol addresses, which you see in disassembly mode and in the Watch window. Be aware of the following regarding symbol addresses on Alpha platforms:

• With Alpha processors, local symbols are usually accessed as offsets from the sp (stack pointer) register, rather than as offsets from the EBP (frame pointer) register as they are on x86 processors running in 32-bit mode. Normally, the symbol names are displayed and the stack pointer offset is hidden. Note that sometimes fp is used, and that there is no EBP on the Alpha platform.
  
  
• If you have set the /Gt compiler option to /Gt0 as recommended, then global symbols smaller than 32 bytes are accessed as offsets from the gp (global pointer) register for faster access. Addresses may, therefore, be displayed as an offset from gp.

  See The /Gt (Set Data Value) Option in Chapter 4 for a detailed discussion about the /Gt switch. See the Alpha Calling Standard for details on when the stack pointer and frame pointer are used.

• On the Alpha platform, when code uses C++ exception handling, structured exception handling, or _ _alloca, local symbols might be accessed as offsets from a frame pointer register (fp).

The following figure shows an example of the Locals window when running on a Alpha platform. Note that each address is an offset from SP, not EBP.

Figure 2.9   The Locals Window on the Alpha Platform