[libiberty] don't demangle functions named "."

[Thiago Jung Bauermann <bauerman at br dot ibm dot com>]

Hi folks,

This patch is to stop the C++ demangler from trying to demangle a symbol
which is not a C++ mangled function.

The problem is happening in Linux/ppc64 with symbols marking the start
of function instructions in the text section, which begin with a dot.
When the function name starts with __, it's symbol will be something
like .__<function name>. If the demangler is able to derive a valid
argument list from <function name>, it will find a demangled "function"
called . with some random argument list. This is happening with several
functions in glibc:

.__frexpf -> .(float, long double,...)(long long, float *)
.__flbf -> .(float, long, bool, float)
.__ffs -> .(float, float, short)
.__ffsll -> .(float, float, short, long, long)
.__sleep -> .(short, long,...)(...)( *)
.__execve -> .(...)(long long,...)(char, void,...)
.__dup -> .(double,  *__restrict)
.__fixdfdi ->  .(float, int, long long, double, float, double, int)
.__fixsfdi -> .(float, int, long long, short, float, double, int)

This is a problem in GDB, for instance when showing a backtrace which
goes through these functions in glibc:

(gdb) bt
#0  0x000004000015edf8 in .__libc_nanosleep () from /lib64/tls/libc.so.6
#1  0x000004000015eb74 in . () from /lib64/tls/libc.so.6
#2  0x0000000010000784 in sleeping_thread (p=0x0) at libc-nanosleep.c:8
(gdb) info symbol 0x000004000015eb74
.(short, long,...)(...)( *) + 148 in section .text

With the patch applied:

(gdb) bt
#0  0x000004000015edf8 in .__libc_nanosleep () from /lib64/tls/libc.so.6
#1  0x000004000015eb74 in .__sleep () from /lib64/tls/libc.so.6
#2  0x0000000010000784 in sleeping_thread (p=0x0) at libc-nanosleep.c:8
(gdb) info symbol 0x000004000015eb74
.__sleep + 148 in section .text

All the libiberty and GDB tests related to demangling continue to pass.

Is this ok?
-- 
[]'s
Thiago Jung Bauermann
Software Engineer
IBM Linux Technology Center

2008-01-09  Thiago Jung Bauermann  <bauerman@br.ibm.com>

	* cplus-dem.c (demangle_function_name): Changed to return value
	indicating if a name was correctly demangled.
	(iterate_demangle_function): Use demangle_function_name return value.

Index: src-git.demangle-fix/libiberty/cplus-dem.c
===================================================================
--- src-git.demangle-fix.orig/libiberty/cplus-dem.c	2008-01-08 15:48:12.000000000 -0200
+++ src-git.demangle-fix/libiberty/cplus-dem.c	2008-01-08 15:48:54.000000000 -0200
@@ -414,7 +414,7 @@ static int do_type (struct work_stuff *,
 
 static int do_arg (struct work_stuff *, const char **, string *);
 
-static void
+static int
 demangle_function_name (struct work_stuff *, const char **, string *,
                         const char *);
 
@@ -2493,10 +2493,7 @@ iterate_demangle_function (struct work_s
      "__"-sequence.  This is the normal case.  */
   if (ARM_DEMANGLING || LUCID_DEMANGLING || HP_DEMANGLING || EDG_DEMANGLING
       || strstr (scan + 2, "__") == NULL)
-    {
-      demangle_function_name (work, mangled, declp, scan);
-      return 1;
-    }
+    return demangle_function_name (work, mangled, declp, scan);
 
   /* Save state so we can restart if the guess at the correct "__" was
      wrong.  */
@@ -2513,10 +2510,12 @@ iterate_demangle_function (struct work_s
 
   while (scan[2])
     {
-      demangle_function_name (work, mangled, declp, scan);
-      success = demangle_signature (work, mangled, declp);
-      if (success)
-	break;
+      if (demangle_function_name (work, mangled, declp, scan))
+	{
+	  success = demangle_signature (work, mangled, declp);
+	  if (success)
+	    break;
+	}
 
       /* Reset demangle state for the next round.  */
       *mangled = mangle_init;
@@ -4421,7 +4420,9 @@ demangle_nested_args (struct work_stuff 
   return result;
 }
 
-static void
+/* Returns 1 if a valid function name was found or 0 otherwise.  */
+
+static int 
 demangle_function_name (struct work_stuff *work, const char **mangled,
                         string *declp, const char *scan)
 {
@@ -4461,13 +4462,13 @@ demangle_function_name (struct work_stuf
 	{
 	  work -> constructor += 1;
 	  string_clear (declp);
-	  return;
+	  return 1;
 	}
       else if (strcmp (declp -> b, "__dt") == 0)
 	{
 	  work -> destructor += 1;
 	  string_clear (declp);
-	  return;
+	  return 1;
 	}
     }
 
@@ -4575,6 +4576,13 @@ demangle_function_name (struct work_stuf
 	    }
 	}
     }
+
+  /* If a function name was obtained but it's not valid, we were not
+     successful.  */
+  if (LEN_STRING (declp) == 1 && declp->b[0] == '.')
+    return 0;
+  else
+    return 1;
 }
 
 /* a mini string-handling package */