[Bug 1489560] Re: qemu-efi: hangs in kvm mode when built w/ gcc-5

[dann frazier]

On Mon, Aug 31, 2015 at 8:24 PM, Thomas Preud'homme
<thomas.preudhomme at arm.com> wrote:
> The commit mentionned in the description concern the bswap pass which is
> enabled at O2 and Os. No need to resort to -O1 though, -fno-expensive-
> optimizations should be enough to disable it.

I tested that and can confirm it is sufficient (see attached patch).


** Patch added: "fno-expensive-optimizations.patch"
   https://bugs.launchpad.net/bugs/1489560/+attachment/4456242/+files/fno-expensive-optimizations.patch

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https://bugs.launchpad.net/bugs/1489560

Title:
  qemu-efi: hangs in kvm mode when built w/ gcc-5

Status in edk2 package in Ubuntu:
  New
Status in gcc-5 package in Ubuntu:
  New

Bug description:
  When I rebuild edk2_0~20150106.5c2d456b-1build1 in wily or sid, KVM-
  accelerated arm64 VMs hang before displaying any console output. I
  bisected this down to a change in gcc (see below).

  Note that this does not impact fully emulated instances. That is, if I
  drop '-enable-kvm' and change '-cpu host' to '-cpu cortex-a57', it
  boots fine.

  Here's the gcc changeset that introduced the issue:

  From 470d5bb5a2aba04db8d9d9dce0c5a3d5efe85882 Mon Sep 17 00:00:00 2001
  From: thopre01 <thopre01 at 138bc75d-0d04-0410-961f-82ee72b054a4>
  Date: Fri, 23 May 2014 03:33:28 +0000
  Subject: [PATCH] 2014-05-23  Thomas Preud'homme  <thomas.preudhomme at arm.com>

          PR tree-optimization/54733
  gcc/
          * tree-ssa-math-opts.c (nop_stats): New "bswap_stats" structure.
          (CMPNOP): Define.
          (find_bswap_or_nop_load): New.
          (find_bswap_1): Renamed to ...
          (find_bswap_or_nop_1): This. Also add support for memory source.
          (find_bswap): Renamed to ...
          (find_bswap_or_nop): This. Also add support for memory source and
          detection of bitwise operations equivalent to load in host endianness.
          (execute_optimize_bswap): Likewise. Also move its leading comment back
          in place and split statement transformation into ...
          (bswap_replace): This.

  gcc/testsuite
          * gcc.dg/optimize-bswapdi-3.c: New test to check extension of bswap
          optimization to support memory sources and bitwise operations
          equivalent to load in host endianness.
          * gcc.dg/optimize-bswaphi-1.c: Likewise.
          * gcc.dg/optimize-bswapsi-2.c: Likewise.
          * gcc.c-torture/execute/bswap-2.c: Likewise.

  
  git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@210843 138bc75d-0d04-0410-961f-82ee72b054a4

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