Ignore __fu<digits>__ symbols from COFF symbol tables

The debugger sometimes prints strange function names for given
addresses. For instance, with the following source code...

	4    procedure Foo is
	5       A : Integer;
	6    begin
	7       Do_Nothing (A'Address);
	8    end Foo;

... we can see...

    (gdb) info line 5
    Line 5 of "foo.adb" starts at address 0x4017ca <_ada_foo+6>
       and ends at 0x4017d2 <_fu29__system__scalar_values__is_is4+7>.
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

_fu29__system__scalar_values__is_is4 is an artificial symbol
generated by the linker, and interferes with the pc-to-symbol
resolution.  There isn't much in the general minimal_symbol
data that could help us identify them, so this patch changes
the COFF reader to simply ignore them.

gdb/ChangeLog:

	* coffread.c (is_import_fixup_symbol): New function.
	(record_minimal_symbol): Use is_import_fixup_symbol to
	detect import fixup symbols, and discard them.

gdb/testsuite/ChangeLog:

        * gdb.ada/win_fu_syms: New testcase.

1 files changed, 43 insertions, 0 deletions

diff --git a/gdb/coffread.c b/gdb/coffread.c
index c390880..eff8d64 100644
--- a/gdb/coffread.c
+++ b/gdb/coffread.c
@@ -418,6 +418,39 @@ coff_end_symtab (struct objfile *objfile)
   set_last_source_file (NULL);
 }
 
+/* The linker sometimes generates some non-function symbols inside
+   functions referencing variables imported from another DLL.
+   Return nonzero if the given symbol corresponds to one of them.  */
+
+static int
+is_import_fixup_symbol (struct coff_symbol *cs,
+			enum minimal_symbol_type type)
+{
+  /* The following is a bit of a heuristic using the characterictics
+     of these fixup symbols, but should work well in practice...  */
+  int i;
+
+  /* Must be a non-static text symbol.  */
+  if (type != mst_text)
+    return 0;
+
+  /* Must be a non-function symbol.  */
+  if (ISFCN (cs->c_type))
+    return 0;
+
+  /* The name must start with "__fu<digits>__".  */
+  if (strncmp (cs->c_name, "__fu", 4) != 0)
+    return 0;
+  if (! isdigit (cs->c_name[4]))
+    return 0;
+  for (i = 5; cs->c_name[i] != '\0' && isdigit (cs->c_name[i]); i++)
+    /* Nothing, just incrementing index past all digits.  */;
+  if (cs->c_name[i] != '_' || cs->c_name[i + 1] != '_')
+    return 0;
+
+  return 1;
+}
+
 static struct minimal_symbol *
 record_minimal_symbol (struct coff_symbol *cs, CORE_ADDR address,
 		       enum minimal_symbol_type type, int section, 
@@ -429,6 +462,16 @@ record_minimal_symbol (struct coff_symbol *cs, CORE_ADDR address,
   if (cs->c_name[0] == '@')
     return NULL;
 
+  if (is_import_fixup_symbol (cs, type))
+    {
+      /* Because the value of these symbols is within a function code
+	 range, these symbols interfere with the symbol-from-address
+	 reverse lookup; this manifests itselfs in backtraces, or any
+	 other commands that prints symbolic addresses.  Just pretend
+	 these symbols do not exist.  */
+      return NULL;
+    }
+
   bfd_section = cs_to_bfd_section (cs, objfile);
   return prim_record_minimal_symbol_and_info (cs->c_name, address,
 					      type, section,