Re: [patch/rfa/hppa] Use frame pointer for unwinding

[Randolph Chung <randolph@tausq.org>]

> What seems to be happening is that the signal handler is triggered
> before the frame pointer is stored in func1:

so, here's my 3rd try ;-)

2004-05-16  Randolph Chung  <tausq@debian.org>

	* hppa-tdep.c (hppa_frame_cache): If a frame pointer is available, use
	it for unwinding the stack.

Index: hppa-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/hppa-tdep.c,v
retrieving revision 1.156
diff -u -p -r1.156 hppa-tdep.c
--- hppa-tdep.c	8 May 2004 03:59:34 -0000	1.156
+++ hppa-tdep.c	17 May 2004 02:29:53 -0000
@@ -1761,15 +1798,42 @@ hppa_frame_cache (struct frame_info *nex
        the current function (and is thus equivalent to the "saved"
        stack pointer.  */
     CORE_ADDR this_sp = frame_unwind_register_unsigned (next_frame, HPPA_SP_REGNUM);
+    CORE_ADDR fp;
 
    if (hppa_debug)
       fprintf_unfiltered (gdb_stdlog, " (this_sp=0x%s, pc=0x%s, "
 		          "prologue_end=0x%s) ",
 		          paddr_nz (this_sp),
 			  paddr_nz (frame_pc_unwind (next_frame)),
 			  paddr_nz (prologue_end));
 
-    if (frame_pc_unwind (next_frame) >= prologue_end)
+    /* Check to see if a frame pointer is available, and use it for
+       frame unwinding if it is.
+
+       There are some situations where we need to rely on the frame
+       pointer to do stack unwinding.  For example, if a function calls
+       alloca (), the stack pointer can get adjusted inside the body of
+       the function.  In this case, the ABI requires that the compiler
+       maintain a frame pointer for the function.
+
+       The unwind record has a flag (alloca_frame) that indicates that
+       a function has a variable frame; unfortunately, gcc/binutils 
+       does not set this flag.  Instead, whenever a frame pointer is used
+       and saved on the stack, the Save_SP flag is set.  We use this to
+       decide whether to use the frame pointer for unwinding.  */
+
+    fp = frame_unwind_register_unsigned (next_frame, HPPA_FP_REGNUM);
+
+    if (frame_pc_unwind (next_frame) >= prologue_end
+        && u->Save_SP && fp != 0)
+      {
+	cache->base = fp;
+
+	if (hppa_debug)
+	  fprintf_unfiltered (gdb_stdlog, " (base=0x%s) [frame pointer] }",
+			      paddr_nz (cache->base));
+      }
+    else if (frame_pc_unwind (next_frame) >= prologue_end)
       {
         if (u->Save_SP && trad_frame_addr_p (cache->saved_regs, HPPA_SP_REGNUM))
           {