-flto causes unresolved reference to __clear_cache

[JC Wren]

When GCC 5.4 2016q3 adds a __clear_cache call and -flto is enabled, ld reports __clear_cache as an unresolved reference.

Target is Cortex-M3 (STM32L151ZD). Attached is a file that will reproduce this issue.

As this uses arm-eabi-none-ar, which requires the --plugin argument when using LTO, I had to copy liblto_plugin-0.dll to the working directory when running under Cygwin. This is also noted in the README.txt file.

This bug report is part of thread https://answers.launchpad.net/gcc-arm-embedded/+question/402728

[Thomas Preud'homme (thomas-preudhomme)]

Hi JC,

We haven't a patch at this point yet but the problem is well understood thanks to your testcase. It only happens when linking static archive so you can work around the issue by either:

- not putting the object file in an archive
- or extracting the elements from the archive for linking

I will let you know once this is fixed.

Best regards,

Thomas

[JC Wren (jcwren)]

Thomas,

From what I can tell, this bug is still in progress, correct?. I gave '6 2017-q2-update' a try, and the error still occurs.

Cheers,
--jc

[Thomas Preud'homme (thomas-preudhomme)]

Hi JC,

The bug is not fixed indeed. As I said the problem is well understood but other issues took priority considering as this can be worked around by avoiding the mix of LTO and static libraries. That said I should report the problem to the GNU ld community so that there's a chance the community could fix it before me.

Best regards.

[JC Wren (jcwren)]

Yah, no problem, just verifying more than anything.

I did convert my project from using a library to linking all the .o files directly. The bootloader links and runs correctly with -flto, but the main application does not run, although it does link. I have not yet had a chance to put it on the debugger and see why it's not starting.

Thanks!

[Joey Ye (jinyun-ye)]

Close it with won't fix as there is a workaround available.