Variable arguments allocation

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Variable arguments allocation

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Dear everybody,

I need to get variable arguments from a function without using va_args.

ABI rules for Nios II state that a copy of r4 thru r7 is saved on the stack

after the function call in order to use va_args.

Now, I make the following call: MyFunction (param1, param2) (the prototype

of MyFunction is void MyFunction (char *, ...). Well, the code written by the

compiler as the prolog of MyFunction is:

addi sp,sp,-32

stw ra,16(sp)

stw fp,12(sp)

mov fp,sp

stw r5,20(fp)

stw r6,24(fp)

stw r7,28(fp)

stw r4,0(fp)

MyFunction uses two "int" local variables. What is really strange for me is that

r4 and r5 (my arguments) are copied at 0(fp) and 20(fp). I expect that r5

is copied at 4(fp). Are you able to explain me this compiler behaviour ?

Best Regards

/Alessandro

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