From: Szabolcs Nagy <nsz@port70.net>
To: musl@lists.openwall.com
Subject: Re: Reviving planned ldso changes
Date: Sun, 26 Feb 2017 16:34:36 +0100 [thread overview]
Message-ID: <20170226153436.GA2082@port70.net> (raw)
In-Reply-To: <20170226152016.GZ1520@brightrain.aerifal.cx>
* Rich Felker <dalias@libc.org> [2017-02-26 10:20:16 -0500]:
> On Sun, Feb 26, 2017 at 11:28:30AM +0100, Szabolcs Nagy wrote:
> > * Rich Felker <dalias@libc.org> [2017-02-25 20:39:26 -0500]:
> > > On Sun, Feb 26, 2017 at 02:04:30AM +0100, Szabolcs Nagy wrote:
> > > > * Rich Felker <dalias@libc.org> [2017-01-15 12:44:38 -0500]:
> > > > > static void do_init_fini(struct dso *p)
> > > > > {
> > > > > size_t dyn[DYN_CNT];
> > > > > - int need_locking = libc.threads_minus_1;
> > > > > - /* Allow recursive calls that arise when a library calls
> > > > > - * dlopen from one of its constructors, but block any
> > > > > - * other threads until all ctors have finished. */
> > > > > - if (need_locking) pthread_mutex_lock(&init_fini_lock);
> > > > > - for (; p; p=p->prev) {
> > > > > - if (p->constructed) continue;
> > > > > + pthread_mutex_lock(&init_fini_lock);
> > > > > + /* Construct in dependency order without any recursive state. */
> > > > > + while (p && !p->constructed) {
> > > > > + /* The following loop descends into the first dependency
> > > > > + * that is neither alredy constructed nor pending
> > > > > + * construction due to circular deps, stopping only
> > > > > + * when it reaches a dso with no remaining dependencies
> > > > > + * to descend into. */
> > > > > + while (p->deps && p->deps[p->next_dep]) {
> > > > > + if (!p->deps[p->next_dep]->constructed &&
> > > > > + !p->deps[p->next_dep]->next_dep)
> > > > > + p = p->deps[p->next_dep++];
> > > > > + else
> > > > > + p->next_dep++;
> > > > > + }
> > > > > p->constructed = 1;
> > > > > decode_vec(p->dynv, dyn, DYN_CNT);
> > > > > if (dyn[0] & ((1<<DT_FINI) | (1<<DT_FINI_ARRAY))) {
> > > > > @@ -1233,17 +1246,19 @@ static void do_init_fini(struct dso *p)
> > > > > size_t *fn = laddr(p, dyn[DT_INIT_ARRAY]);
> > > > > while (n--) ((void (*)(void))*fn++)();
> > > > > }
> > > > > - if (!need_locking && libc.threads_minus_1) {
> > > > > - need_locking = 1;
> > > > > - pthread_mutex_lock(&init_fini_lock);
> > > > > - }
> > > > > - }
> > > > > - if (need_locking) pthread_mutex_unlock(&init_fini_lock);
> > > > > + /* Revisit "parent" dso which caused the just-constructed
> > > > > + * dso to be pulled in as a dependency. On the next loop
> > > > > + * iteration we will either descend to construct a sibling
> > > > > + * of the just-constructed dso, or finish constructing the
> > > > > + * parent if no unfinished deps remain. */
> > > > > + p = p->needed_by;
> > > > > + }
> > > >
> > > > i think with
> > > >
> > > > a.deps: b c
> > > > b.deps: c d
> > > > b.needed_by: a
> > > > c.needed_by: a
> > > >
> > > > the visiting order starting from a is
> > > > a
> > > > b
> > > > c
> > > > a
> > > >
> > > > and d never gets constructed.
> > >
> > > Are you sure? My understanding of what it does is:
> > >
> > > 1. Descend a->b->c, construct c, and back up to b.
> >
> > you did not explain how you get back to b after c
> > without a stack of visited dsos or modified c->needed_by.
>
> Sorry, that should have been back up to a (c->needed_by). Then:
>
> 2. Descend a->b->d, construct d, and back up to b.
>
> The key point is that x->needed_by is always the first dso that pulled
> in x, so if we back all the way back up to x->needed_by, we'll revisit
> all later dsos which depend on x.
for that a->b transition has to happen twice,
but a.next_dep is already past b the second
time a is visited, so i still don't see why
this works.
next prev parent reply other threads:[~2017-02-26 15:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-03 5:43 Rich Felker
2017-01-04 6:06 ` Rich Felker
2017-01-04 6:22 ` Rich Felker
2017-01-04 19:36 ` Rich Felker
2017-01-14 21:30 ` A. Wilcox
2017-01-15 17:44 ` Rich Felker
2017-02-26 1:04 ` Szabolcs Nagy
2017-02-26 1:39 ` Rich Felker
2017-02-26 10:28 ` Szabolcs Nagy
2017-02-26 15:20 ` Rich Felker
2017-02-26 15:34 ` Szabolcs Nagy [this message]
2017-02-26 21:39 ` Rich Felker
2017-03-03 1:30 ` Rich Felker
2017-03-04 10:58 ` Szabolcs Nagy
2017-03-06 1:11 ` Rich Felker
2017-03-07 22:02 ` Rich Felker
2017-03-08 18:55 ` Rich Felker
2017-03-06 16:25 ` Rich Felker
2017-01-04 10:51 ` Szabolcs Nagy
2017-02-16 1:58 ` Szabolcs Nagy
2017-02-16 2:39 ` Rich Felker
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170226153436.GA2082@port70.net \
--to=nsz@port70.net \
--cc=musl@lists.openwall.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).