How does it compile if you change the C code to this?:
int main(void) __attribute__ ((naked)) __attribute__ ((section
(".init9")));
int main()
{
uint8_t ch;
for (;;) {
ch = getch();
if(ch == STK_GET_PARAMETER) {
register uint8_t which = getch();
register uint8_t output = 0x03;
verifySpace();
if (which == 0x82) {
output = OPTIBOOT_MINVER;
} else if (which == 0x81) {
output = OPTIBOOT_MAJVER;
}
putch(output);
}
That should help make it somewhat immune to the vagaries of the
optimizer, but also keep the generated code small.
Let me know what you get.
Eric Weddington
> -----Original Message-----
> From: avr-gcc-list-bounces+eric.weddington=atmel....@nongnu.org
[mailto:avr-
> gcc-list-bounces+eric.weddington=atmel....@nongnu.org] On Behalf Of
William
> "Chops" Westfield
> Sent: Thursday, January 26, 2012 11:11 AM
> To: avr-gcc-list@nongnu.org
> Subject: [avr-gcc-list] Weird optimization issue with avr-gcc 4.5.3,re
> "naked."
>
> A week or so ago I mentioned that avr-gcc 4.5.3 caused the optiboot
bootloader
> (used by Arduino and etc) to grow 22 bytes (from 500 bytes to 522
bytes,
> pushing it over the size that it needs to be.)
>
> This took a while to track down, because it's weird. Apparently gcc
is
> optimizing code differently depending on whether the function is
defined as
> "naked" or not. Optiboot sets up main() as naked to save space, and
the lost
> optimization is hurting it.
>
> I have a small test case (even smaller than optiboot :-)
> (files also attached. foo.c, foo-naked.S, foo-clothed.S)
>
> Consider:
>
> int main(void) __attribute__ ((naked)) __attribute__ ((section
(".init9")));
> int main()
> {
> uint8_t ch;
>
> for (;;) {
> ch = getch();
>
> if(ch == STK_GET_PARAMETER) {
> register uint8_t which = getch();
> verifySpace();
> if (which == 0x82) {
> putch(OPTIBOOT_MINVER);
> } else if (which == 0x81) {
> putch(OPTIBOOT_MAJVER);
> } else {
> putch(0x03);
> }
> }
>
> Without the extra attributes for main, the is optimized to fact out
the call
> to putch():
>
> /*
> * Send optiboot version as "minor SW version"
> */
> putch(OPTIBOOT_MINVER);
> 1c: 85 e0 ldi r24, 0x05 ; 5
> 1e: 00 c0 rjmp .+0 ; 0x20 <main+0x20>
> } else if (which == 0x81) {
> 20: 81 38 cpi r24, 0x81 ; 129
> 22: 01 f4 brne .+0 ; 0x24 <main+0x24>
> putch(OPTIBOOT_MAJVER);
> 24: 84 e0 ldi r24, 0x04 ; 4
> 26: 00 c0 rjmp .+0 ; 0x28 <main+0x28>
> } else {
> /*
> * GET PARAMETER returns a generic 0x03 reply for
> * other parameters - enough to keep Avrdude happy
> */
> putch(0x03);
> 28: 83 e0 ldi r24, 0x03 ; 3
> 2a: 00 d0 rcall .+0 ; 0x2c <main+0x2c>
> 2c: 00 c0 rjmp .+0 ; 0x2e <main+0x2e>
> }
> }
>
> WITH the extra attributes, I get three separate rcall instructions:
>
> putch(OPTIBOOT_MINVER);
> 12: 85 e0 ldi r24, 0x05 ; 5
> 14: 00 d0 rcall .+0 ; 0x16 <main+0x16>
> 16: 00 c0 rjmp .+0 ; 0x18 <main+0x18>
> } else if (which == 0x81) {
> 18: 81 38 cpi r24, 0x81 ; 129
> 1a: 01 f4 brne .+0 ; 0x1c <main+0x1c>
> putch(OPTIBOOT_MAJVER);
> 1c: 84 e0 ldi r24, 0x04 ; 4
> 1e: 00 d0 rcall .+0 ; 0x20 <main+0x20>
> 20: 00 c0 rjmp .+0 ; 0x22 <main+0x22>
> } else {
> /*
> * GET PARAMETER returns a generic 0x03 reply for
> * other parameters - enough to keep Avrdude happy
> */
> putch(0x03);
> 22: 83 e0 ldi r24, 0x03 ; 3
> 24: 00 d0 rcall .+0 ; 0x26 <main+0x26>
> 26: 00 c0 rjmp .+0 ; 0x28 <main+0x28>
> }
> }
>
> Any thoughts as to what might be going on here?
>
> Thanks
> WestfW
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