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Re: [PATCH] Async signal safe TLS accesses
- From: Andrew Hunter <ahh at google dot com>
- To: Rich Felker <dalias at aerifal dot cx>
- Cc: Ian Lance Taylor <iant at google dot com>, "Joseph S. Myers" <joseph at codesourcery dot com>, "Carlos O'Donell" <carlos at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>, Paul Pluzhnikov <ppluzhnikov at google dot com>
- Date: Wed, 2 Oct 2013 16:17:04 -0700
- Subject: Re: [PATCH] Async signal safe TLS accesses
- Authentication-results: sourceware.org; auth=none
- References: <523F2ED8 dot 8090909 at redhat dot com> <1379977289-21260-1-git-send-email-ahh at google dot com> <20130924025738 dot GK20515 at brightrain dot aerifal dot cx> <524C3467 dot 2030503 at redhat dot com> <Pine dot LNX dot 4 dot 64 dot 1310022203420 dot 22120 at digraph dot polyomino dot org dot uk> <CAKOQZ8wN0ecYROnxNT5edV5yxr5jiAuoLVg4ErO9DZq3SYj4HQ at mail dot gmail dot com> <20131002223612 dot GA20515 at brightrain dot aerifal dot cx> <CADroS=6qkwBbdq8M0Lq7_k0p3oB+asnhcPnEyrrzu65MUAd0rQ at mail dot gmail dot com> <20131002225311 dot GB20515 at brightrain dot aerifal dot cx> <CADroS=4E1f2UOJa5_QCHr+9-P1ksXmrKbyXPVrWmEgL0o=diYg at mail dot gmail dot com> <20131002231443 dot GE20515 at brightrain dot aerifal dot cx>
On Wed, Oct 2, 2013 at 4:14 PM, Rich Felker <email@example.com> wrote:
> On Wed, Oct 02, 2013 at 04:03:01PM -0700, Andrew Hunter wrote:
>> On Wed, Oct 2, 2013 at 3:53 PM, Rich Felker <firstname.lastname@example.org> wrote:
>> > Since when does dlopen support initial-exec? I am not aware of any
>> > such support, and it certainly can't work in general since the needed
>> > address range might not even be available.
>> It certainly does since at least 2.15; I haven't searched the history
>> for its initial creation. It, indeed, can fail; by default glibc
>> appears to allocate 1600 bytes/thread for "surplus" initial-exec TLS
>> (that is, that which is found in dlopen'd objects); dlopen will fail
>> if that is exhausted.
> In that case, our current discussion does not apply. TLS allocated
> into the "surplus" initial TLS zone would be handled the same as it is
> now, not via anything new under present discussion.
Except that this zone has to be initialized in all threads by
dlopen--it _cannot_ be done lazily on first access as you suggest for
I agree that my patch doesn't change this meaningfully, I'm just
saying that this feature means we absolutely must iterate and update
living threads, something you wanted to avoid.