Re: [PATCH] Fix gdb1476.exp on s390*

[Andrew Cagney <cagney@gnu.org>]

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> Andrew Cagney wrote:
> 
> 
>>>> > Hello,
>>>> > 
>>>> > this patch fixes the gdb.base/gdb1476.exp test case (backtrace from NULL
>>>> > function pointer call).
>>>> > 
>>>> > When calling via an invalid function pointer, what we should do is simply
>>>> > unwind the PC from the return address register and continue.  This is
>>>> > exactly what is done to unwind from a PLT stub as well, so the patch 
>>>> > simply uses the PLT frame unwinder to handle this case as well.
>>
>>> 
>>> While that might be true, I don't know that its the job of something 
>>> called "PLTSTUB".  
> 
> 
> Yes, the name's a bit unfortunate.  What this unwinder does is basically
> unwind from any situation where we don't have a proper function prolog.
> It could in theory handle all kinds of stubs, trampolines etc.
> 
> 
>>> I can think of either:
>>> - renaming pltstub to something that matches its new purpose (just "stub"?)
> 
> 
> This would be my preferred solution.

Try the attached.

Andrew

>>> - using the default unwinder
> 
> 
> The default unwinder as it is now would handle the situation incorrectly.
> I could build the stub detection logic into the default unwinder, but that
> would make it even more complex than it already is; I would think with the
> new frame logic it is preferable to have multiple unwinders rather than a
> single one that handles everything.
> 
> Bye,
> Ulrich


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2004-03-22  Andrew Cagney  <cagney@redhat.com>

	* s390-tdep.c (struct s390_stub_unwind_cache): Rename
	s390_pltstub_unwind_cache.
	(s390_stub_frame_unwind_cache): Rename
	s390_pltstub_frame_unwind_cache.
	(s390_stub_frame_this_id): Rename s390_pltstub_frame_this_id.
	(s390_stub_frame_prev_register): Rename
	s390_pltstub_frame_prev_register.
	(s390_stub_frame_unwind): Rename s390_pltstub_frame_unwind.
	(s390_stub_frame_sniffer): Rename s390_stub_frame_sniffer.

	From Ulrich Weigand:
	* s390-tdep.c (s390_pltstub_frame_sniffer): Handle invalid function
	pointer calls like PLT calls.

Index: s390-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/s390-tdep.c,v
retrieving revision 1.129
diff -u -r1.129 s390-tdep.c
--- s390-tdep.c	26 Feb 2004 23:48:01 -0000	1.129
+++ s390-tdep.c	22 Mar 2004 21:55:33 -0000
@@ -2037,27 +2037,29 @@
 }
 
 
-/* PLT stub stack frames.  */
-
-struct s390_pltstub_unwind_cache {
+/* Code stubs and their stack frames.  For things like PLTs and NULL
+   function calls (where there is no true frame and the return address
+   is in the RETADDR register).  */
 
+struct s390_stub_unwind_cache
+{
   CORE_ADDR frame_base;
   struct trad_frame_saved_reg *saved_regs;
 };
 
-static struct s390_pltstub_unwind_cache *
-s390_pltstub_frame_unwind_cache (struct frame_info *next_frame,
-				 void **this_prologue_cache)
+static struct s390_stub_unwind_cache *
+s390_stub_frame_unwind_cache (struct frame_info *next_frame,
+			      void **this_prologue_cache)
 {
   struct gdbarch *gdbarch = get_frame_arch (next_frame);
   int word_size = gdbarch_ptr_bit (gdbarch) / 8;
-  struct s390_pltstub_unwind_cache *info;
+  struct s390_stub_unwind_cache *info;
   ULONGEST reg;
 
   if (*this_prologue_cache)
     return *this_prologue_cache;
 
-  info = FRAME_OBSTACK_ZALLOC (struct s390_pltstub_unwind_cache);
+  info = FRAME_OBSTACK_ZALLOC (struct s390_stub_unwind_cache);
   *this_prologue_cache = info;
   info->saved_regs = trad_frame_alloc_saved_regs (next_frame);
 
@@ -2072,41 +2074,47 @@
 }
 
 static void
-s390_pltstub_frame_this_id (struct frame_info *next_frame,
-			    void **this_prologue_cache,
-			    struct frame_id *this_id)
+s390_stub_frame_this_id (struct frame_info *next_frame,
+			 void **this_prologue_cache,
+			 struct frame_id *this_id)
 {
-  struct s390_pltstub_unwind_cache *info
-    = s390_pltstub_frame_unwind_cache (next_frame, this_prologue_cache);
+  struct s390_stub_unwind_cache *info
+    = s390_stub_frame_unwind_cache (next_frame, this_prologue_cache);
   *this_id = frame_id_build (info->frame_base, frame_pc_unwind (next_frame));
 }
 
 static void
-s390_pltstub_frame_prev_register (struct frame_info *next_frame,
-				  void **this_prologue_cache,
-				  int regnum, int *optimizedp,
-				  enum lval_type *lvalp, CORE_ADDR *addrp,
-				  int *realnump, void *bufferp)
+s390_stub_frame_prev_register (struct frame_info *next_frame,
+			       void **this_prologue_cache,
+			       int regnum, int *optimizedp,
+			       enum lval_type *lvalp, CORE_ADDR *addrp,
+			       int *realnump, void *bufferp)
 {
-  struct s390_pltstub_unwind_cache *info
-    = s390_pltstub_frame_unwind_cache (next_frame, this_prologue_cache);
+  struct s390_stub_unwind_cache *info
+    = s390_stub_frame_unwind_cache (next_frame, this_prologue_cache);
   trad_frame_prev_register (next_frame, info->saved_regs, regnum,
                             optimizedp, lvalp, addrp, realnump, bufferp);
 }
 
-static const struct frame_unwind s390_pltstub_frame_unwind = {
+static const struct frame_unwind s390_stub_frame_unwind = {
   NORMAL_FRAME,
-  s390_pltstub_frame_this_id,
-  s390_pltstub_frame_prev_register
+  s390_stub_frame_this_id,
+  s390_stub_frame_prev_register
 };
 
 static const struct frame_unwind *
-s390_pltstub_frame_sniffer (struct frame_info *next_frame)
+s390_stub_frame_sniffer (struct frame_info *next_frame)
 {
-  if (!in_plt_section (frame_pc_unwind (next_frame), NULL))
-    return NULL;
+  CORE_ADDR pc = frame_pc_unwind (next_frame);
+  bfd_byte insn[S390_MAX_INSTR_SIZE];
 
-  return &s390_pltstub_frame_unwind;
+  /* If the current PC points to non-readable memory, we assume we
+     have trapped due to an invalid function pointer call.  We handle
+     the non-existing current function like a PLT stub.  */
+  if (in_plt_section (pc, NULL)
+      || s390_readinstruction (insn, pc) < 0)
+    return &s390_stub_frame_unwind;
+  return NULL;
 }
 
 
@@ -3028,7 +3036,7 @@
   dwarf2_frame_set_init_reg (gdbarch, s390_dwarf2_frame_init_reg);
   frame_unwind_append_sniffer (gdbarch, dwarf2_frame_sniffer);
   frame_base_append_sniffer (gdbarch, dwarf2_frame_base_sniffer);
-  frame_unwind_append_sniffer (gdbarch, s390_pltstub_frame_sniffer);
+  frame_unwind_append_sniffer (gdbarch, s390_stub_frame_sniffer);
   frame_unwind_append_sniffer (gdbarch, s390_sigtramp_frame_sniffer);
   frame_unwind_append_sniffer (gdbarch, s390_frame_sniffer);
   frame_base_set_default (gdbarch, &s390_frame_base);