Build failure with v4.9-rc1 and GCC trunk -- compiler weirdness

[Markus Trippelsdorf]

On 2016.10.17 at 19:38 +0100, Will Deacon wrote:
> Hi all,
> 
> I'm seeing an arm64 build failure with -rc1 and GCC trunk, although I
> believe that the new compiler behaviour at the heart of the problem
> has the potential to affect other architectures and other pieces of
> kernel code relying on dead-code elimination to remove deliberately
> undefined functions.
> 
> The failure looks like:
> 
>   | drivers/built-in.o: In function `armada_3700_add_composite_clk':
>   |
>   | linux/drivers/clk/mvebu/armada-37xx-periph.c:351:
>   | undefined reference to `____ilog2_NaN'
>   |
>   | linux/drivers/clk/mvebu/armada-37xx-periph.c:351:(.text+0xc72e0):
>   | relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol
>   | `____ilog2_NaN'
>   |
>   | make: *** [vmlinux] Error 1
> 

This is a gcc bug, see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785

-- 
Markus