Re: [patch/rfc] signal trampoline frames

[Andrew Cagney <cagney@gnu.org>]

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see attached?

> 
>>> +static CORE_ADDR
>>> +tramp_frame_start (CORE_ADDR pc, const struct tramp_frame *tramp)
>>> +{
>>> +  int ti;
>>> +  /* Search through the trampoline for one that matches the
>>> +     instruction sequence around PC.  */
>>> +  for (ti = 0; tramp->insn[ti] != 0; ti++)
>>> +    {
>>> +      CORE_ADDR func = pc - tramp->insn_size * ti;
>>> +      int i;
>>> +      for (i = 0; 1; i++)
>>> +	{
>>> +	  bfd_byte buf[sizeof (LONGEST)];
>>> +	  CORE_ADDR insn;
> 
> 
> tramp->insn is a ULONGEST.  Both of these should probably be ULONGEST
> also.

changed to ->insn[0]

> 
>>> +	  if (tramp->insn[i] == 0)
>>> +	    return func;
> 
> 
> So zeros in tramp->insn mark the end of the sequence?  Should document
> that, zeros are valid instructions and some bizarre architecture might
> use one as a syscall trap.

Added TRAMP_SENTINEL_INSN, it _isn't_ zero.

>>> +  /* If the function has a valid symbol name, it isn't a
>>> +     trampoline.  */
>>> +  find_pc_partial_function (pc, &name, NULL, NULL);
>>> +  if (name != NULL)
>>> +    return 0;
>>> +  /* If the function lives in a valid section (even without a starting
>>> +     point) it isn't a trampoline.  */
>>> +  if (find_pc_section (pc) != NULL)
>>> +    return 0;
> 
> 
> I believe the first check is redundant to the second check; can we have
> names without sections?  I may be wrong about this, remembering the
> problem on IRIX with absolute sections.

I don't know.

Andrew


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2004-03-23  Andrew Cagney  <cagney@redhat.com>

	* tramp-frame.h (TRAMP_SENTINEL_INSN): Define, document.
	* tramp-frame.c: Include "gdb_assert.h".
	(tramp_frame_start): Use TRAMP_SENTINEL_INSN.
	(tramp_frame_append): Assert the presence of TRAMP_SENTINEL_INSN.
	* Makefile.in (tramp-frame.o): Update dependencies.

Index: Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/Makefile.in,v
retrieving revision 1.529
diff -u -r1.529 Makefile.in
--- Makefile.in	23 Mar 2004 14:12:30 -0000	1.529
+++ Makefile.in	23 Mar 2004 23:58:05 -0000
@@ -2449,7 +2449,7 @@
 	$(regcache_h)
 tramp-frame.o: tramp-frame.c $(defs_h) $(tramp_frame_h) $(frame_unwind_h) \
 	$(gdbcore_h) $(symtab_h) $(objfiles_h) $(target_h) $(trad_frame_h) \
-	$(frame_base_h)
+	$(frame_base_h) $(gdb_assert_h)
 typeprint.o: typeprint.c $(defs_h) $(gdb_obstack_h) $(bfd_h) $(symtab_h) \
 	$(gdbtypes_h) $(expression_h) $(value_h) $(gdbcore_h) $(command_h) \
 	$(gdbcmd_h) $(target_h) $(language_h) $(cp_abi_h) $(typeprint_h) \
Index: tramp-frame.c
===================================================================
RCS file: /cvs/src/src/gdb/tramp-frame.c,v
retrieving revision 1.2
diff -u -r1.2 tramp-frame.c
--- tramp-frame.c	23 Mar 2004 14:12:30 -0000	1.2
+++ tramp-frame.c	23 Mar 2004 23:58:06 -0000
@@ -28,6 +28,7 @@
 #include "target.h"
 #include "trad-frame.h"
 #include "frame-base.h"
+#include "gdb_assert.h"
 
 struct frame_data
 {
@@ -89,15 +90,15 @@
   int ti;
   /* Search through the trampoline for one that matches the
      instruction sequence around PC.  */
-  for (ti = 0; tramp->insn[ti] != 0; ti++)
+  for (ti = 0; tramp->insn[ti] != TRAMP_SENTINEL_INSN; ti++)
     {
       CORE_ADDR func = pc - tramp->insn_size * ti;
       int i;
       for (i = 0; 1; i++)
 	{
-	  bfd_byte buf[sizeof (LONGEST)];
+	  bfd_byte buf[sizeof (tramp->insn[0])];
 	  CORE_ADDR insn;
-	  if (tramp->insn[i] == 0)
+	  if (tramp->insn[i] == TRAMP_SENTINEL_INSN)
 	    return func;
 	  if (target_read_memory (func + i * tramp->insn_size, buf,
 				  tramp->insn_size) != 0)
@@ -148,6 +149,15 @@
 {
   struct frame_data *data;
   struct frame_unwind *unwinder;
+  int i;
+
+  /* Check that the instruction sequence contains a sentinel.  */
+  for (i = 0; i < ARRAY_SIZE (tramp_frame->insn); i++)
+    {
+      if (tramp_frame->insn[i] == TRAMP_SENTINEL_INSN)
+	break;
+    }
+  gdb_assert (i < ARRAY_SIZE (tramp_frame->insn));
 
   data = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_data);
   unwinder = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_unwind);
Index: tramp-frame.h
===================================================================
RCS file: /cvs/src/src/gdb/tramp-frame.h,v
retrieving revision 1.2
diff -u -r1.2 tramp-frame.h
--- tramp-frame.h	23 Mar 2004 14:12:30 -0000	1.2
+++ tramp-frame.h	23 Mar 2004 23:58:06 -0000
@@ -39,6 +39,10 @@
 
 /* A trampoline descriptor.  */
 
+/* Magic instruction that to mark the end of the signal trampoline
+   instruction sequence (zero for the moment).  */
+#define TRAMP_SENTINEL_INSN ((LONGEST) -1)
+
 struct tramp_frame
 {
   /* The trampoline's entire instruction sequence.  Search for this in
@@ -47,7 +51,8 @@
      one INSN_SIZE instruction.  It is also assumed that TRAMP[0]
      contains the first instruction of the trampoline and hence the
      address of the instruction matching TRAMP[0] is the trampoline's
-     "func" address.  */
+     "func" address.  The instruction sequence shall be terminated by
+     TRAMP_SENTINEL_INSN.  */
   int insn_size;
   ULONGEST insn[8];
   /* Initialize a trad-frame cache corresponding to the tramp-frame.