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[avr-gcc-list] Not naked but "topless" functions?

From: Tvrtko A. Ursulin
Subject: [avr-gcc-list] Not naked but "topless" functions?
Date: Thu, 10 Oct 2002 23:07:52 +0200

Hello everyone!

More questions...

I need to write functions that dont push/pop registers on stack. But if I use 
__attribute__((naked)) then compiler omits code that adjusts stack pointer 
also. That is ok if my function uses less than available registers, but if 
not... trouble.

My functions should adjust stack like this:

 14e:   cd b7           in      r28, 0x3d       ; 61
 150:   de b7           in      r29, 0x3e       ; 62
 152:   25 97           sbiw    r28, 0x05       ; 5
 154:   0f b6           in      r0, 0x3f        ; 63
 156:   f8 94           cli
 158:   de bf           out     0x3e, r29       ; 62
 15a:   0f be           out     0x3f, r0        ; 63
 15c:   cd bf           out     0x3d, r28       ; 61

This is taken from function which uses 5 stack variables, hence sbiw r28,0x05.

Btw, what does in/cli/out of SREG in default function prolog do? If it is 
supposed to ensure no interrupt occurs while manipulating SP, why "out 
0x3f,r0" (enable interrupts right?) is not the last instruction? 


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