[PATCH] Fixing get_builder() function in dwarf2/read.c

watashiwaher
2020-06-14T16:49:33Z

Explanation
I found that some binaries with debug symbols halt gdb. And the problem was
in the get_builder() function inside dwarf2/read.c file. The function
recursively called itself until infinity. So I tried to fix this issue by
eliminating recursion and adding the check for cycle detection, and
returning nullptr if cycle detected.

ChangeLog
2020-06-15 Slava Mitin <watashiwaher@gmail.com>

* dwarf2/read.c (get_builder): Added check for cycles

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index e3073fe43c..e8c6d3bec3 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -594,15 +594,51 @@ struct dwarf2_cu
/* Get the buildsym_compunit for this CU. */
buildsym_compunit *get_builder ()
{
- /* If this CU has a builder associated with it, use that. */
- if (m_builder != nullptr)
- return m_builder.get ();
+ /* Number of iterations before the updating of
+ the recursion_check_cu pointer */
+ const int RECURSION_CHECK_UPDATE_INTERVAL = 2;

- /* Otherwise, search ancestors for a valid builder. */
- if (ancestor != nullptr)
- return ancestor->get_builder ();
+ /* Replacing recursion calls of get_builder
+ to the loop */
+ dwarf2_cu *current_cu = this;

- return nullptr;
+ /* Sometimes CUs can include each other recuresively,
+ so we need to stop iterating some day, if they do */
+ dwarf2_cu *recursion_check_cu = nullptr;
+
+ /* Counter of intervals */
+ int recursion_check_counter = 1;
+
+ while (true) {
+ /* If this CU has a builder associated with it, use that. */
+ if (current_cu->m_builder != nullptr) {
+ return current_cu->m_builder.get();
+ }
+
+ /* Otherwise, search ancestors for a valid builder. */
+ if (current_cu->ancestor != nullptr) {
+ current_cu = current_cu->ancestor;
+ } else {
+ return nullptr;
+ }
+
+ /* If CU was seen already, return. */
+ if (recursion_check_cu == current_cu) {
+ return nullptr;
+ }
+
+ /* Update the variable used to check the recursion */
+ if (recursion_check_counter == RECURSION_CHECK_UPDATE_INTERVAL) {
+ if (recursion_check_cu == nullptr) {
+ recursion_check_cu = this;
+ } else {
+ recursion_check_cu = recursion_check_cu->ancestor;
+ }
+ recursion_check_counter = 1;
+ } else {
+ recursion_check_counter++;
+ }
+ }
}
};