Link Time Optimisation 6.2.0 about homebrew-avr

[tuna-f1sh]

Appears to be a bug in the compiler. The Arch package had the same problem. There is a work around but seems to be fixed in the latest avr-libc? An issue in the Arduino repository too.

[ladislas]

that's super interesting! :)

maybe using avr-gcc 6.3.0 and Binutils 2.26.1 will fix the issue?

https://gcc.gnu.org/gcc-6/changes.html

[ladislas]

Just tried and it doesn't work...

here is my test case: https://github.com/ladislas/Bare-Arduino-Project/tree/lto-bug

on branch lto-bug in ./src/BarProject just run make on OSX.

[larsimmisch]

@tuna-f1sh: can you show a minimal example of the compile/link rules in your Makefile? In particular, do you use ld for linking or gcc?

Note to self: I'm not sure what causes this, because -enable-lto is the default according to https://gcc.gnu.org/install/configure.html. But there are some mentions that LTO is a linker plugin, so we may have to make sure the gcc lto plugin is picked up by binutils.

[ladislas]

I have the same issue. Did not notice it before as i was overriding the flags.

[larsimmisch]

@tuna-f1sh Just looked at Arduino-mk: disregard my question. $(CC) is invoked as the linker

[larsimmisch]

The underlying issue seems to be this (arduino/Arduino#660 (comment)):

Small update: lto build on 6.1 segfaults on libraries using virtual inheritance. Hence, adding -fno-devirtualize to c and cpp extra flags solves the segfault.

I would argue that this is a gcc bug - whatever it does, it should not segfault. Can you try compiling with -fno-devirtualize and -flto?

In any case, this should probably be reported to gcc and it looks as if the best we can do right now is to suggest workarounds - and removing -flto does work for you.

Have you got time to prepare a minimal reproduction case?

[larsimmisch]

@ladislas yes, good idea. But we need a reproducible test case

[ladislas]

@tuna-f1sh this is being discussed here: sudar/Arduino-Makefile#486

updating arduino-mk should fix the issue.