[PHP-DEV] [Jakub Jelinek <jakub <<i>email protected</i>>>] [PATCH] (fwd) email protected>>] [PATCH] (fwd)",1); ?> From: Rasmus Lerdorf (rasmus <email protected>)
Date: 09/27/01

This came across the glibc dev list. Thought it was interesting that PHP
is stressing the dlopen code.

-Rasmus

------- Start of forwarded message -------
Date: Thu, 27 Sep 2001 15:55:40 +0200
From: Jakub Jelinek <jakub <email protected>>
To: Ulrich Drepper <drepper <email protected>>
Cc: Glibc hackers <libc-hacker <email protected>>
Subject: [PATCH]
Message-ID: <20010927155540.B3251 <email protected>>
Reply-To: Jakub Jelinek <jakub <email protected>>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii

Hi!

httpd -X -DHAVE_PHP4 crashes with current CVS glibc.
httpd basically dlopens a whole lot of modules, some of which contain many
dependencies, forks, dlcloses most of the stuff and dlopens everything
again. I've tracked the problem to the new dl-open.c code, where it assumes
that when opening new, all its freshly opened dependencies have l_opencount
0. But as the check is done after relocation processing, l_opencount might
be bumped because of relocation dependency. If this happens, dl_open_worker
adds new to the dependency's l_scope eventhough it was added there by
_dl_new_object when it was created (since new is that dependency's ultimate
loader). This is both inefficient (too long search scope) and causes the
crash (since code in dl-close.c only removes one copy from l_scope, one copy
will remain and thus l_scope[1] points to random garbage).
Here is one possible fix (for freshly loaded dependency last entry in
l_scope will be its ultimate loader and thus we can just compare that
against what we would add), another would be to alloca a old_opencount array
and save there l_opencount entries of each l_searchlist member before
relocating and check that instead of l_opencount later on when testing
whether it should be added to l_scope.
I'll try to cook up a testcase.

2001-09-27 Jakub Jelinek <jakub <email protected>>

        * elf/dl-open.c (dl_open_worker): If l_opencount of freshly loaded
        object has been bumped because of relocation dependency, avoid
        duplicates in l_scope.
        (show_scope): Fix typos.

--- libc/elf/dl-open.c.jj Thu Sep 27 09:25:14 2001
+++ libc/elf/dl-open.c Thu Sep 27 09:32:12 2001
@@ -316,6 +316,12 @@ dl_open_worker (void *a)
             ++runp;
           }

+ /* This can happen if imap was just loaded, but during relocation
+ had l_opencount bumped because of relocation dependency.
+ Avoid duplicates in l_scope. */
+ if (__builtin_expect (runp [-1] == &new->l_searchlist, 0))
+ continue;
+
         if (__builtin_expect (cnt + 1 >= imap->l_scope_max, 0))
           {
             /* The 'r_scope' array is too small. Allocate a new one
@@ -478,11 +484,11 @@ show_scope (struct link_map *new)

       for (cnt = 0; cnt < new->l_scope[scope_cnt]->r_nlist; ++cnt)
         if (*new->l_scope[scope_cnt]->r_list[cnt]->l_name)
- _dl_printf (" %s", new->l_scope[scope_cnt]->r_list[cnt]->l_name)
+ _dl_printf (" %s", new->l_scope[scope_cnt]->r_list[cnt]->l_name);
         else
- _dl_printf (" <main>", NULL);
+ _dl_printf (" <main>");

- _dl_printf ("\n", NULL);
+ _dl_printf ("\n");
     }
 }
 #endif

        Jakub

------- End of forwarded message ------- 

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