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To: Suraj Jitindar Singh <sjitindarsingh@gmail.com>, linuxppc-dev@ozlabs.org
From: Michael Ellerman <mpe@ellerman.id.au>
Cc: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Subject: Re: selftests/powerpc: Remove -flto from common CFLAGS
Message-Id: <20160229111013.71B58140779@ozlabs.org>
Date: Mon, 29 Feb 2016 22:10:13 +1100 (AEDT)
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Hi Suraj,

On Mon, 2016-29-02 at 06:29:55 UTC, Suraj Jitindar Singh wrote:
> LTO can cause GCC to inline some functions which have attributes set. The

You should define what LTO is the first time you use it.

> act of inlining the functions can lead to GCC forgetting about the
> attributes which leads to incorrect tests.
> Notable example being: __attribute__((__target__("no-vsx")))

That is probably a GCC bug, but we still need to work around it for now.

> LTO can also interact strangely with custom assembly functions and cause
> tests to intermittently fail.

That's probably Cyril writing bad asm :)

> Both these cases are hard to detect and require manual inspection of
> binaries which is unlikely to happen for all tests. Furthermore, LTO
> optimisations are not necessary for selftests and correctness is paramount
> and as such it is best to disable LTO.
> 
> LTO can be enabled on a per test basis.
> 
> A pseries_le_defconfig kernel on a POWER8 was used to determine that the
> same subset of selftests pass and fail with and without -flto in the
> common Makefile.
> 
> These tests always fail:
> selftests: per_event_excludes [FAIL]
> selftests: event_attributes_test [FAIL]
> selftests: ebb_vs_cpu_event_test [FAIL]
> selftests: cpu_event_vs_ebb_test [FAIL]
> selftests: cpu_event_pinned_vs_ebb_test [FAIL]

They shouldn't :)

Are you running as root? Bare metal or guest?

> selftests: ipc_unmuxed [FAIL]

That one is expected.

cheers