From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cagney <cagney@gnu.org>
To: Randolph Chung <randolph@tausq.org>
Cc: gdb-patches@sources.redhat.com
Subject: Re: [patch/rfa/hppa] Use frame pointer for unwinding
Date: Mon, 17 May 2004 15:23:00 -0000
Message-id: <40A8D8E5.9000506@gnu.org>
References: <20040516020703.GZ566@tausq.org> <40A78B63.9020102@gnu.org> <20040516170257.GM566@tausq.org> <20040517001310.GO566@tausq.org> <20040517023428.GP566@tausq.org>
X-SW-Source: 2004-05/msg00489.html

+    /* 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)
fp will effectively always be non-zero here, so the ``fp != 0'' is a 
just-in-case?  Suggest adding that, and the GCC bug-number, as additions 
to the comments.

+      {
+	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)
otherwize ok

Andrew