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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