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6.1.8 Processor mapping of registers

This indicates what registers are used for what purposes on each of the processors supported by Free Pascal. It also indicates which registers can be used as scratch registers.

Intel 80x86 version

Table 6.1: Intel 80x86 Register table

Generic register name CPU Register name
accumulator EAX
accumulator (64-bit) high / low EDX:EAX
float result FP(0)
self ESI
frame pointer EBP
stack pointer ESP
scratch regs. N/A
OS_128 type (128 bit integer) RDX:RAX
Motorola 680x0 version

Table 6.2: Motorola 680x0 Register table

Generic register name CPU Register name
accumulator D02
accumulator (64-bit) high / low D0:D1
float result FP03
self A5
frame pointer A6
stack pointer A7
scratch regs. D0, D1, A0, A1, FP0, FP1

2For compatibility with some C compilers, when the function result is a pointer and is declared with the cdecl convention, the result is also stored in the A0 register

3On simulated FPU’s the result is returned in D0

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