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Re: [avr-gcc-list] Incorrect code by gcc?

From: Ruud Vlaming
Subject: Re: [avr-gcc-list] Incorrect code by gcc?
Date: Thu, 3 Apr 2008 00:51:59 +0200
User-agent: KMail/1.9.1

On Thursday 03 April 2008 00:27, Andy H wrote:
> Not a bug
Very good spotting. Andy! Thank you!

Thats the reason i wanted it to post here before sending in a bug report.
Unfortunately i already did so, so i marked the bug as INVALID now.
The bugnumber was 35807 

> According to the sources you posted,
> privQueuRequestBody
> void privQueuRequestBody(uint8_t uiSlot, int8_t siFreeFilling, uint16_t 
> uiTicksToWait) __attribute__ ( ( naked ) );
> The relevant part being "naked"
> That means gcc will omit prolog - which is where stack and frame pointer are 
> setup.
> R28/29 is the frame pointer. What you see in assembler is gcc saving the 
> register around a call. 
> Depending on optimization, it may choose to do this rather than use a 
> register (as the register would need to be saved on the stack). 
> If you use naked, you must replace all of prolog/epilog by hand. (its normal 
> use is for assembler only functions)

OK, naked is a "dangerous" attribute. I must use it for i do a context save 
just before the
body function is called, but must preserve all registers so the function 
parameters are 
left alone. 

Is there a way to prohibit the compiler to do so? In other words can i somehow 
to make use of the frame pointer? -fomit-frame-pointer seems not to do the 

Since i know on beforehand i will not return from privQueuRequestBody there is 
need to save the stack or so. 



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