Discovered on Arduino (4.9.2-atmel3.5.4) ( http://forum.arduino.cc/index.php?topic=556674.0 ) So I have this pretty trivial avr-gcc program:
#include <avr/io.h>
void serialEvent() __attribute__((weak));
void loop();
void serialEventRun(void)
{
#ifndef OMITBUG
if (serialEvent) serialEvent();
#endif
}
int main() {
for (;;) {
loop();
if (serialEventRun) serialEventRun();
}
}
int nnn = 1;
void loop()
{
if (nnn <= 3) {
char rrr = 0;
while ( !rrr ) {
if (PORTB)
rrr = (PORTB == 'c' );
}
PORTB |= 1 << 5;
nnn++;
} else while (1);
}
If compile with "avr-gcc -g -Os -flto -mmcu=atmega328p bug.c -o bug.elf" it
will produce code that omits the test for (nnn <= 3)
Turning off -flto, or adding -DOMITBUG to the compile line (removing the
call to the non-existent serialEvent() function) results in correct code.
Discovered on Arduino (4.9.2-atmel3.5.4) (
http://forum.arduino.cc/index.php?topic=556674.0 )
Also fails with avr-gcc (AVR_8_bit_GNU_Toolchain_3.6.1_496) 5.4.0 and
avr-gcc (AVR_8_bit_GNU_Toolchain_3.6.1_1750) 5.4.0
With avr-gcc 8.1, it produce an additional error that may or may not be
relevant:
C:\Users\billw\Documents\src>\bin\avr-gcc-8.1.0-x86-mingw\bin\avr-gcc -g
-Os -flto -mmcu=atmega328p bug.c -o bug.elf
C:\Users\billw\AppData\Local\Temp\ccE52smMdebugobjtem: file not recognized:
File truncated
collect2.exe: error: ld returned 1 exit status
lto-wrapper.exe: fatal error: \bin\avr-gcc-8.1.0-x86-mingw\bin\avr-gcc
returned 1 exit status
compilation terminated.
c:/bin/avr-gcc-8.1.0-x86-mingw/bin/../lib/gcc/avr/8.1.0/../../../../avr/bin/ld.exe:
error: lto-wrapper failed
collect2.exe: error: ld returned 1 exit status
(8.1 files in ld even with -DOMITBUG, though slightly differenty. It works
without -flto)
Um. Wild guess: The if (serialEvent) serialEvent(); line generates
slightly odd code, including a call to an absolute address of 0x0.
Is there something in link that uses a 0x0 address as an "end of list"
indicator?
ba: 20 97 sbiw r28, 0x00 ; 0
bc: 71 f3 breq .-36 ; 0x9a <main+0x4>
be: 0e 94 00 00 call 0 ; 0x0 <__vectors>
-save-temp data attached for both working and fail cases.
<<attachment: gcc-lto-bug.zip>>
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