From eec4126c312ab709df64df48fa6db99339e9ea54 Mon Sep 17 00:00:00 2001
From: kevinb <kevinb>
Date: Sat, 26 Feb 2000 09:30:30 +0000
Subject: [PATCH] Changes to skip_prologue for PPC architecture.

---
 gdb/ChangeLog     | 13 +++++++++++++
 gdb/rs6000-tdep.c | 38 +++++++++++++++++++++++++++-----------
 2 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b3b3c265d4..36dc637b17 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,16 @@
+2000-02-26  Kevin Buettner  <kevinb@redhat.com>
+
+	* ppc-linux-tdep.c (ppc_linux_memory_remove_breakpoint): Add
+	comment explaining motivation behind this function and why
+	the generic facilities won't work for this platform.
+	* rs6000-tdep.c (skip_prologue): Always test to make sure
+	that an instruction is read successfully from the target's
+	memory.  Introduce notion of instructions which may appear in
+	the prologue, but may not end the prologue.  Added explicit
+	check for nop instruction.  Use memset() to zero the frame
+	data instead of assignment from a statically allocated,
+	uninitialized structure.
+
 Sat Feb 26 17:15:16 2000  Andrew Cagney  <cagney@b1.cygnus.com>
 
 	* MAINTAINERS: Chris Faylor is responsible for all MS Windows
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index ca094c74cf..c3cd31b75e 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -305,11 +305,10 @@ rs6000_software_single_step (signal, insert_breakpoints_p)
 #define GET_SRC_REG(x) (((x) >> 21) & 0x1f)
 
 CORE_ADDR
-skip_prologue (pc, fdata)
-     CORE_ADDR pc;
-     struct rs6000_framedata *fdata;
+skip_prologue (CORE_ADDR pc, struct rs6000_framedata *fdata)
 {
   CORE_ADDR orig_pc = pc;
+  CORE_ADDR last_prologue_pc;
   char buf[4];
   unsigned long op;
   long offset = 0;
@@ -318,24 +317,31 @@ skip_prologue (pc, fdata)
   int reg;
   int framep = 0;
   int minimal_toc_loaded = 0;
-  static struct rs6000_framedata zero_frame;
+  int prev_insn_was_prologue_insn = 1;
 
-  *fdata = zero_frame;
+  memset (fdata, 0, sizeof (struct rs6000_framedata));
   fdata->saved_gpr = -1;
   fdata->saved_fpr = -1;
   fdata->alloca_reg = -1;
   fdata->frameless = 1;
   fdata->nosavedpc = 1;
 
-  if (target_read_memory (pc, buf, 4))
-    return pc;			/* Can't access it -- assume no prologue. */
-
-  /* Assume that subsequent fetches can fail with low probability.  */
   pc -= 4;
   for (;;)
     {
       pc += 4;
-      op = read_memory_integer (pc, 4);
+
+      /* Sometimes it isn't clear if an instruction is a prologue
+         instruction or not.  When we encounter one of these ambiguous
+	 cases, we'll set prev_insn_was_prologue_insn to 0 (false).
+	 Otherwise, we'll assume that it really is a prologue instruction. */
+      if (prev_insn_was_prologue_insn)
+	last_prologue_pc = pc;
+      prev_insn_was_prologue_insn = 1;
+
+      if (target_read_memory (pc, buf, 4))
+	break;
+      op = extract_signed_integer (buf, 4);
 
       if ((op & 0xfc1fffff) == 0x7c0802a6)
 	{			/* mflr Rx */
@@ -375,6 +381,16 @@ skip_prologue (pc, fdata)
 	  continue;
 
 	}
+      else if ((op & 0xffff0000) == 0x60000000)
+        {
+	  			/* nop */
+	  /* Allow nops in the prologue, but do not consider them to
+	     be part of the prologue unless followed by other prologue
+	     instructions. */
+	  prev_insn_was_prologue_insn = 0;
+	  continue;
+
+	}
       else if ((op & 0xffff0000) == 0x3c000000)
 	{			/* addis 0,0,NUM, used
 				   for >= 32k frames */
@@ -564,7 +580,7 @@ skip_prologue (pc, fdata)
 #endif /* 0 */
 
   fdata->offset = -fdata->offset;
-  return pc;
+  return last_prologue_pc;
 }
 
 
-- 
2.11.0