[PATCH] preserve base pointer for __deregister_frame [PR110956]

[Thomas Neumann via Gcc-patches]

Original bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110956
Rainer Orth successfully tested the patch on Solaris with a full bootstrap.


Some uncommon unwinding table encodings need to access the base pointer
for address computations. We do not have that information in calls to
__deregister_frame_info_bases, and previously simply used nullptr as
base pointer. That is usually fine, but for some Solaris i386 shared
libraries that results in wrong address computations.

To fix this problem we now associate the unwinding object with
the table pointer itself, which is always known, in addition to
the PC range. When deregistering a frame, we first locate the object
using the table pointer, and then use the base pointer stored within
the object to compute the PC range.

libgcc/ChangeLog:
        PR libgcc/110956
        * unwind-dw2-fde.c: Associate object with address of unwinding
        table.
---
 libgcc/unwind-dw2-fde.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/libgcc/unwind-dw2-fde.c b/libgcc/unwind-dw2-fde.c
index d7c4a467754..ae4530179f3 100644
--- a/libgcc/unwind-dw2-fde.c
+++ b/libgcc/unwind-dw2-fde.c
@@ -124,6 +124,9 @@ __register_frame_info_bases (const void *begin, struct 
object *ob,
 #endif
 
 #ifdef ATOMIC_FDE_FAST_PATH
+  // Register the object itself to know the base pointer on deregistration.
+  btree_insert (&registered_frames, (uintptr_type) begin, 1, ob);
+
   // Register the frame in the b-tree
   uintptr_type range[2];
   get_pc_range (ob, range);
@@ -175,6 +178,9 @@ __register_frame_info_table_bases (void *begin, struct 
object *ob,
   ob->s.b.encoding = DW_EH_PE_omit;
 
 #ifdef ATOMIC_FDE_FAST_PATH
+  // Register the object itself to know the base pointer on deregistration.
+  btree_insert (&registered_frames, (uintptr_type) begin, 1, ob);
+
   // Register the frame in the b-tree
   uintptr_type range[2];
   get_pc_range (ob, range);
@@ -225,22 +231,17 @@ __deregister_frame_info_bases (const void *begin)
     return ob;
 
 #ifdef ATOMIC_FDE_FAST_PATH
-  // Find the corresponding PC range
-  struct object lookupob;
-  lookupob.tbase = 0;
-  lookupob.dbase = 0;
-  lookupob.u.single = begin;
-  lookupob.s.i = 0;
-  lookupob.s.b.encoding = DW_EH_PE_omit;
-#ifdef DWARF2_OBJECT_END_PTR_EXTENSION
-  lookupob.fde_end = NULL;
-#endif
-  uintptr_type range[2];
-  get_pc_range (&lookupob, range);
+  // Find the originally registered object to get the base pointer.
+  ob = btree_remove (&registered_frames, (uintptr_type) begin);
 
-  // And remove
-  ob = btree_remove (&registered_frames, range[0]);
-  bool empty_table = (range[1] - range[0]) == 0;
+  // Remove the corresponding PC range.
+  if (ob)
+    {
+      uintptr_type range[2];
+      get_pc_range (ob, range);
+      if (range[0] != range[1])
+       btree_remove (&registered_frames, range[0]);
+    }
 
   // Deallocate the sort array if any.
   if (ob && ob->s.b.sorted)
@@ -283,12 +284,11 @@ __deregister_frame_info_bases (const void *begin)
 
  out:
   __gthread_mutex_unlock (&object_mutex);
-  const int empty_table = 0; // The non-atomic path stores all tables.
 #endif
 
   // If we didn't find anything in the lookup data structures then they
   // were either already destroyed or we tried to remove an empty range.
-  gcc_assert (in_shutdown || (empty_table || ob));
+  gcc_assert (in_shutdown || ob);
   return (void *) ob;
 }
 
--
2.39.2