Bootstrap Calling Convention

The entire bootstrap image is downloaded into memory starting at location 07C00h. The preboot code transfers control to the bootstrap by executing a far call to the beginning of the bootstrap code. At this point the following must be true:

• CS:IP is to contain the value 0:7C00h
  
  
• ES:BX is to contain the address of the PXENV Entry Point structure described in the “Preboot API Entry Point and Installation Check” section later in this attachment
  
  
• EDX is to contain the physical address of the PXENV Entry Point structure
  
  
• SS:SP is to contain the address of the beginning of the unused portion of the preboot services stack

  Note that the bootstrap code can determine how much free stack space is available by examining the contents of SP and by having knowledge of the memory usage conventions described in the following section.

  Caution: A bootstrap should not exceed 32 KB in length. The memory between 07C00h and 10000h is free for use by the bootstrap.