http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56533
Bug #: 56533
Summary: Linker problem on avr with lto and main function
inside archive
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: [email protected]
ReportedBy: [email protected]
When trying to add lto to my Arduino program, it stopped compiling complaining
about missing symbols. I've managed to reduce the problem to below minimal
example. Note that removing anything from below example makes the problem
disappear. In particular, the problem disappears when:
* any of the linker options is removed: -mmcu=atmega328p -Os -flto
-fwhole-program
* the -flto compiler option is removed
* using normal gcc (amd64) instead of avr-gcc
* linking main.o instead of main.a
* declaring realmain as externally_visible in realmain.c
Note that in this example, the actual main() function is inside an archive,
which is probably the reason for this bug / problem.
$ avr-gcc --version
avr-gcc (GCC) 4.7.2
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ avr-ld --version
GNU ld (GNU Binutils) 2.20.1.20100303
Copyright 2009 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later
version.
This program has absolutely no warranty.
$ cat main.c
int realmain(void);
int main(void)
{
return realmain();
}
$ cat realmain.c
int realmain(void) {
}
$ cat do
#!/bin/sh
set -x
rm -f main.a
/usr/bin/avr-gcc -c main.c -o main.o
/usr/bin/avr-ar rcs main.a main.o
/usr/bin/avr-gcc -c -flto realmain.c -o realmain.o
/usr/bin/avr-gcc -mmcu=atmega328p -Os -flto -fwhole-program realmain.o
main.a
$ ./do
+ rm -f main.a
+ /usr/bin/avr-gcc -c main.c -o main.o
+ /usr/bin/avr-ar rcs main.a main.o
+ /usr/bin/avr-gcc -c -flto realmain.c -o realmain.o
+ /usr/bin/avr-gcc -mmcu=atmega328p -Os -flto -fwhole-program realmain.o
main.a
main.a(main.o): In function `main':
main.c:(.text+0x8): undefined reference to `realmain'
collect2: error: ld returned 1 exit status
