Re: [PATCH] sched: Work around undefined behavior in sched class checking

On Tue, May 04, 2021 at 08:39:45PM -0700, Andi Kleen wrote:

From: Andi Kleen <redacted>

The scheduler initialization code checks that the scheduling
classes are consecutive in memory by comparing the end
addresses with the next address.

Technically in ISO C comparing symbol addresseses outside different objects
is undefined. With LTO gcc 10 tries to exploits this and creates an
unconditional BUG_ON in the scheduler initialization, resulting
in a boot hang.

Use RELOC_HIDE to make this work. This hides the symbols from gcc,
so the optimizer won't make these assumption. I also split
the BUG_ONs in multiple.

Urgh, that insanity again :/ Can't we pretty please get a GCC flag to
disable that?