Re: [avr-gcc-list] Weird optimization issue with avr-gcc 4.5.3, re "naked."

[Georg-Johann Lay]

William "Chops" Westfield schrieb:

> 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.)
>
>
> Any thoughts as to what might be going on here?
>
> Thanks WestfW

I tested the code with avr-gcc 4.5 and command line options -Os 
-mmcu=atmega8

With the attributes, the object size is 54 bytes.
Without the attributes the object size is 64 bytes.

If you get > 500 bytes you should turn on optimization.

The difference between 54 and 64 is because main's prologue is not void 
if it's not naked.

Herer is a diff between the respective assembler files:

 __SP_L__ = 0x3d
 __tmp_reg__ = 0
 __zero_reg__ = 1
-       .section        .init9,"ax",@progbits
+       .text
 .global        main
        .type   main, @function
 main:
-/* prologue: naked */
+       push r29
+       push r28
+       push __tmp_reg__
+       in r28,__SP_L__
+       in r29,__SP_H__
+/* prologue: function */
 /* frame size = 1 */
-/* stack size = 0 */
-.L__stack_usage = 0
+/* stack size = 3 */
+.L__stack_usage = 3
 .L7:
        rcall getch
        cpi r24,lo8(24)

So you see it's all about prologue and naked, the code is the same.

Johann