From: Luke Diamand <ldiamand@roku.com>
To: elfutils-devel@sourceware.org
Cc: Florian Weimer <fweimer@redhat.com>,
Mark Wielaard <mark@klomp.org>, Luke Diamand <ldiamand@roku.com>
Subject: [PATCHv2 1/1] report_r_debug: handle `-z separate-code' and find more modules
Date: Fri, 12 May 2023 20:11:45 +0100 [thread overview]
Message-ID: <20230512191145.936984-2-ldiamand@roku.com> (raw)
In-Reply-To: <20230512191145.936984-1-ldiamand@roku.com>
Looking at some cores in eu-stack, I found that they were not being
backtraced.
This was because elfutils had not found some modules (e.g. libc-2.22.so)
in report_r_debug.
That is because it has a limit on the number of link map entries it will
look at, to avoid loops in corrupted core files.
The example I found had:
- 36 elements
- 109 iterations
See also discussion here:
https://sourceware.org/pipermail/elfutils-devel/2023q2/006149.html
Signed-off-by: Luke Diamand <ldiamand@roku.com>
---
libdwfl/link_map.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 06d85eb6..76f23354 100644
--- a/libdwfl/link_map.c
+++ b/libdwfl/link_map.c
@@ -331,11 +331,17 @@ report_r_debug (uint_fast8_t elfclass, uint_fast8_t elfdata,
int result = 0;
/* There can't be more elements in the link_map list than there are
- segments. DWFL->lookup_elts is probably twice that number, so it
- is certainly above the upper bound. If we iterate too many times,
- there must be a loop in the pointers due to link_map clobberation. */
+ segments. A segment is created for each PT_LOAD and there can be
+ up to 5 per module (-z separate-code, tends to create four LOAD
+ segments, gold has -z text-unlikely-segment, which might result
+ in creating that number of load segments) DWFL->lookup_elts is
+ probably twice the number of modules, so that multiplied by max
+ PT_LOADs is certainly above the upper bound. If we iterate too
+ many times, there must be a loop in the pointers due to link_map
+ clobberation. */
+#define MAX_PT_LOAD 5
size_t iterations = 0;
- while (next != 0 && ++iterations < dwfl->lookup_elts)
+ while (next != 0 && ++iterations < dwfl->lookup_elts * MAX_PT_LOAD)
{
if (read_addrs (&memory_closure, elfclass, elfdata,
&buffer, &buffer_available, next, &read_vaddr,
--
2.40.1
next prev parent reply other threads:[~2023-05-12 19:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-12 19:11 [PATCHv2 0/1] In report_r_debug, iterate more segments Luke Diamand
2023-05-12 19:11 ` Luke Diamand [this message]
2023-05-12 20:08 ` [PATCHv2 1/1] report_r_debug: handle `-z separate-code' and find more modules Mark Wielaard
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