Ok you should not be using naked.
If function never returns (I mean never!) then it should be something
like this :
void main(void) __attribute__((noreturn));
-fomit-frame-pointer will work if gcc can really omit it.
Frame pointer will be used to store "local" variables that are to big to fit in
registers and/or need to be saved around calls.
It may also use R2-R17 to save values. Many factors determine which it will
use, such as loops - speed -size - overhead of saving registers etc.
It is not always perfect.
If you find situation where it could omit frame pointer - but does not, that
might be a bug
(gcc is not perfect - I know several parts that could be better).
By all means post "bug" here first if you are not sure.
I know gcc bugs should have pre-processed sources (.i files) - but as first
look it is easier to just look at c code.
I think Eric and others would have spotted it sooner.
best regards and hope tulips look good.
Andy
Ruud Vlaming wrote:
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 forbid
to make use of the frame pointer? -fomit-frame-pointer seems not to do the trick.
Since i know on beforehand i will not return from privQueuRequestBody there is
no
need to save the stack or so.
Ideas?
Ruud.
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