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_dl_build_local_scope - BZ #20488
- From: Mark Hatle <mark dot hatle at windriver dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Cc: Alexander Miller <alex dot miller at gmx dot de>
- Date: Fri, 19 Aug 2016 21:01:33 -0500
- Subject: _dl_build_local_scope - BZ #20488
- Authentication-results: sourceware.org; auth=none
This is somewhat a followup to Alexander Miller's email for a few months back:
https://sourceware.org/ml/libc-alpha/2016-05/msg00034.html
Independently we identify a similar problem with the emulated rtld in the cross
prelinker. The ELF spec indicates that the symbol resolution is breadth first,
not depth first. Without doing this a failure can occur.
The current prelinker (git://git.yoctoproject.org/prelink-cross) has a specific
test case for the ordering issue. See 'order' test case.
The patch below fixes the issue in glibc and was developed independently. My
employer (Wind River) has a copyright assigned with the FSF if the change is
substantial enough to require one.
The patch is attached to BZ 20488, as well as included below.
>From 6e4ec5a3c5fe63b6458036f18d43124de4a7e724 Mon Sep 17 00:00:00 2001
From: Mark Hatle <mark.hatle@windriver.com>
Date: Thu, 18 Aug 2016 14:07:58 -0500
Subject: [PATCH] elf/dl-deps.c: Make _dl_build_local_scope breadth first
According to the ELF specification:
When resolving symbolic references, the dynamic linker examines the symbol
tables with a breadth-first search.
This function was using a depth first search. By doing so the conflict
resolution reported to the prelinker (when LD_TRACE_PRELINKING=1 is set)
was incorrect. This caused problems when their were various circular
dependencies between libraries. The problem usually manifested itself by
the wrong IFUNC being executed.
Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
---
elf/dl-deps.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/elf/dl-deps.c b/elf/dl-deps.c
index 6a82987..fc37c87 100644
--- a/elf/dl-deps.c
+++ b/elf/dl-deps.c
@@ -73,13 +73,19 @@ _dl_build_local_scope (struct link_map **list, struct
link_map *map)
{
struct link_map **p = list;
struct link_map **q;
+ struct link_map **r;
*p++ = map;
map->l_reserved = 1;
- if (map->l_initfini)
- for (q = map->l_initfini + 1; *q; ++q)
- if (! (*q)->l_reserved)
- p += _dl_build_local_scope (p, *q);
+
+ for (r = list; r < p; ++r)
+ if ((*r)->l_initfini)
+ for (q = (*r)->l_initfini + 1; *q; ++q)
+ if (! (*q)->l_reserved)
+ {
+ *p++ = *q;
+ (*q)->l_reserved = 1;
+ }
return p - list;
}
--
2.5.5