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Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646

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On Fri, Apr 15, 2016 at 12:05:26PM -0700, James Bottomley wrote:
> On Fri, 2016-04-15 at 20:56 +0200, Denys Vlasenko wrote:
> > and now *many* users of qla2x00 and new-ish gcc are going to
> > very much notice it, as their kernels will start crashing reliably.
> > 
> > The commits can be reverted, sure, but they per se do not contain
> > anything unusual. They, together with not very typical construct
> > in qla2x00_get_host_fabric_name, one
> > which boils down to "swab64p(constant_array_of_8_bytes)",
> > just happen to nudge gcc in a right way to finally trigger the bug.
> > 
> > So I came with another idea how to forestall the imminent deluge of
> > qla2x00 oops reports - this patch.
> 
> There are actually a raft of checkers that run the upstream code which
> aren't seeing any problem; likely because the code is harder to trigger
> than you think.  So, lets wait until the resolution of the other thread
> before we panic, especially since we're only at -rc3.

Regardless of the outcome of the gcc bug, it seems kind of silly to
byteswap a constant value of 0xffffffffffffffff.

	uint8_t node_name[WWN_SIZE] = { 0xFF, 0xFF, 0xFF, 0xFF, \
		0xFF, 0xFF, 0xFF, 0xFF};
	u64 fabric_name = wwn_to_u64(node_name);

Similar to what Denys suggested, it can just be:

	u64 fabric_name = -1;
or
	u64 fabric_name = 0xffffffffffffffff;

Wouldn't that be an improvement to the code regardless?

-- 
Josh

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[PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 Denys Vlasenko <dvlasenk@redhat.com> - 2016-04-15 12:40 +0200
  Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 James Bottomley <James.Bottomley@HansenPartnership.com> - 2016-04-15 16:50 +0200
    Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 Denys Vlasenko <dvlasenk@redhat.com> - 2016-04-15 21:00 +0200
      Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 James Bottomley <James.Bottomley@HansenPartnership.com> - 2016-04-15 21:10 +0200
        Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-15 22:10 +0200
          Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 James Bottomley <James.Bottomley@HansenPartnership.com> - 2016-04-15 23:20 +0200
        Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 Denys Vlasenko <dvlasenk@redhat.com> - 2016-04-15 23:20 +0200
          Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 James Bottomley <James.Bottomley@HansenPartnership.com> - 2016-04-15 23:30 +0200

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