From: Jonathan Wakely <jwakely@redhat.com>
To: Richard Henderson <rth@redhat.com>
Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: Re: [libstdc++/65033] Give alignment info to libatomic
Date: Wed, 18 Feb 2015 12:15:00 -0000 [thread overview]
Message-ID: <20150218121512.GI3360@redhat.com> (raw)
In-Reply-To: <54DD19B7.6060401@redhat.com>
On 12/02/15 13:23 -0800, Richard Henderson wrote:
>When we fixed PR54005, making sure that atomic_is_lock_free returns the same
>value for all objects of a given type, we probably should have changed the
>interface so that we would pass size and alignment rather than size and object
>pointer.
>
>Instead, we decided that passing null for the object pointer would be
>sufficient. But as this PR shows, we really do need to take alignment into
>account.
>
>The following patch constructs a fake object pointer that is maximally
>misaligned. This allows the interface to both the builtin and to libatomic to
>remain unchanged. Which probably makes this back-portable to maintenance
>releases as well.
Am I right in thinking that another option would be to ensure that
std::atomic<> objects are always suitably aligned? Would that make
std::atomic<> slightly more compatible with a C11 atomic_int, where
the _Atomic qualifier affects alignment?
https://gcc.gnu.org/PR62259 suggests we might need to enforce
alignment on std::atomic anyway, or am I barking up the wrong tree?
next prev parent reply other threads:[~2015-02-18 12:15 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-12 21:23 Richard Henderson
2015-02-18 12:15 ` Jonathan Wakely [this message]
2015-03-25 16:22 ` Jonathan Wakely
2015-03-25 18:36 ` Richard Henderson
2015-03-25 18:49 ` Jonathan Wakely
2015-03-25 19:04 ` Richard Henderson
2015-03-26 13:21 ` Jonathan Wakely
2015-03-31 13:41 ` Jonathan Wakely
2015-03-31 14:54 ` Richard Henderson
2015-03-31 15:03 ` Jonathan Wakely
2015-03-31 15:13 ` Richard Henderson
2015-03-31 15:41 ` Jonathan Wakely
2015-04-06 22:59 ` Hans-Peter Nilsson
2015-04-13 4:45 ` patch fix issue 1 with "[libstdc++/65033] Give alignment info to libatomic" Hans-Peter Nilsson
2015-04-13 11:59 ` Jonathan Wakely
2015-04-13 5:59 ` Issue 2 " Hans-Peter Nilsson
2015-04-13 17:53 ` Joseph Myers
2015-03-25 18:39 ` [libstdc++/65033] Give alignment info to libatomic Richard Henderson
2015-04-03 3:04 ` Hans-Peter Nilsson
2015-03-26 11:54 ` Jonathan Wakely
2015-04-03 3:57 ` Hans-Peter Nilsson
2015-04-03 9:25 ` Hans-Peter Nilsson
2015-04-03 14:13 ` Jonathan Wakely
2015-04-03 19:13 ` Richard Henderson
2015-04-07 13:14 ` Jonathan Wakely
2015-04-09 11:17 ` Jonathan Wakely
2015-04-06 1:07 ` Hans-Peter Nilsson
2015-04-07 9:45 ` Jonathan Wakely
2015-04-07 10:52 ` Hans-Peter Nilsson
2015-04-07 13:12 ` Jonathan Wakely
2015-04-07 14:51 ` Hans-Peter Nilsson
2015-04-07 15:06 ` Jonathan Wakely
2015-04-08 3:58 ` Hans-Peter Nilsson
2015-04-08 9:35 ` Jonathan Wakely
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