report_r_debug: handle `-z separate-code' and find more modules

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>

diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 06d85eb617c9d501e6cb6e4a406067833def32a0..76f2335462a7d493cdc8ba91371df969c97925ef 100644 (file)
--- 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,