[PATCH 13/16] libdw: Make libdw_findcu thread-safe

[Mark Wielaard]

From: Heather McIntyre <h...@rice.edu>

        * libdw/libdw_findcu.c (findcu_cb): Use eu_tsearch.
        (__libdw_findcu): Use eu_tfind and next_tucu_offset_lock.
        (__libdw_findcu_addr): Use eu_tfind.
        (__libdw_find_split_dbg_addr): Likewise.

Signed-off-by: Heather S. McIntyre <h...@rice.edu>
Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 libdw/libdw_findcu.c | 54 ++++++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 19 deletions(-)

diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
index ed744231..e546fb0f 100644
--- a/libdw/libdw_findcu.c
+++ b/libdw/libdw_findcu.c
@@ -32,9 +32,13 @@
 #endif
 
 #include <assert.h>
-#include <search.h>
+#include <eu-search.h>
 #include "libdwP.h"
 
+/* __libdw_findcu modifies "&dbg->next_tu_offset : &dbg->next_cu_offset".
+   May read or write, so mutual exclusion is enforced to prevent a race. */
+rwlock_define(static, next_tucu_offset_lock);
+
 static int
 findcu_cb (const void *arg1, const void *arg2)
 {
@@ -213,7 +217,7 @@ __libdw_intern_next_unit (Dwarf *dbg, bool debug_types)
     Dwarf_Sig8_Hash_insert (&dbg->sig8_hash, unit_id8, newp);
 
   /* Add the new entry to the search tree.  */
-  if (tsearch (newp, tree, findcu_cb) == NULL)
+  if (eu_tsearch (newp, tree, findcu_cb) == NULL)
     {
       /* Something went wrong.  Undo the operation.  */
       *offsetp = oldoff;
@@ -234,28 +238,40 @@ __libdw_findcu (Dwarf *dbg, Dwarf_Off start, bool 
v4_debug_types)
 
   /* Maybe we already know that CU.  */
   struct Dwarf_CU fake = { .start = start, .end = 0 };
-  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
+  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
+  struct Dwarf_CU *result = NULL;
+
   if (found != NULL)
     return *found;
 
-  if (start < *next_offset)
-    {
-      __libdw_seterrno (DWARF_E_INVALID_DWARF);
-      return NULL;
-    }
+  rwlock_wrlock(next_tucu_offset_lock);
 
-  /* No.  Then read more CUs.  */
-  while (1)
+  if (start < *next_offset)
+    __libdw_seterrno (DWARF_E_INVALID_DWARF);
+  else
     {
-      struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg, v4_debug_types);
-      if (newp == NULL)
-       return NULL;
+      /* No.  Then read more CUs.  */
+      while (1)
+       {
+         struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg,
+                                                           v4_debug_types);
+         if (newp == NULL)
+           {
+             result = NULL;
+             break;
+           }
 
-      /* Is this the one we are looking for?  */
-      if (start < *next_offset || start == newp->start)
-       return newp;
+         /* Is this the one we are looking for?  */
+         if (start < *next_offset || start == newp->start)
+           {
+             result = newp;
+             break;
+           }
+       }
     }
-  /* NOTREACHED */
+
+  rwlock_unlock(next_tucu_offset_lock);
+  return result;
 }
 
 struct Dwarf_CU *
@@ -283,7 +299,7 @@ __libdw_findcu_addr (Dwarf *dbg, void *addr)
     return NULL;
 
   struct Dwarf_CU fake = { .start = start, .end = 0 };
-  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
+  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
 
   if (found != NULL)
     return *found;
@@ -298,7 +314,7 @@ __libdw_find_split_dbg_addr (Dwarf *dbg, void *addr)
   /* XXX Assumes split DWARF only has CUs in main IDX_debug_info.  */
   Elf_Data fake_data = { .d_buf = addr, .d_size = 0 };
   Dwarf fake = { .sectiondata[IDX_debug_info] = &fake_data };
-  Dwarf **found = tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
+  Dwarf **found = eu_tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
 
   if (found != NULL)
     return *found;
-- 
2.41.0