Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 23)

CS485G Spring 2015 23

11. Linkage at the calling point for swap(&course1, &course2);

subl $8,%esp # make room for two parameters

movl $course2, 4%esp) # parameter 2

movl $course1, (%esp) # parameter 1

call swap # call

12. When a procedure is called, after the procedure pushes %ebp, the

following values apply.

location meaning

0(%esp) old %ebp

4(%esp) return address

8(%esp) ﬁrst parameter

12(%esp) second parameter

13. If a local register, such as %ebx, has then been pushed, the %esp

rameters.

23 Register-saving conventions

1. The compiler writer determines what registers are meant to survive

procedure calls (”non-volatile registers”) and which can be used for

temporary storage by the procedure (”volatile registers”).

2. This convention prevents one procedure call from corrupting an-

other’s data.

3. Say A (the caller) is calling B (the callee).

(a) If A has been using a volatile register, it must save it (on the

stack) before calling B, and pop it when B returns. This situation

is called caller save.

(b) If B needs to use a non-volatile register, it should save it (on the

stack) before doing its work and pop it before returning. This

situation is called callee save.

4. The convention that gcc follows for the x86:

(a) %eax, %ecx, %edx are volatile (caller-save) general-purpose reg-

isters.

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Cirrus Logic CS485 Manual de usuario Pagina 23