src/gdb/ChangeLog:

2006-03-28  Jim Blandy  <jimb@codesourcery.com>

	* prologue-value.c, prologue-value.h: New files.
	* Makefile.in (prologue_value_h): New variable.
	(HFILES_NO_SRCDIR): List prologue-value.h.
	(SFILES): List prologue-value.c.
	(COMMON_OBS): List prologue-value.o.
	(prologue-value.o): New rule.

src/gdb/doc/ChangeLog:
2006-03-28  Jim Blandy  <jimb@codesourcery.com>

	* gdbint.texinfo (Prologue Analysis): New section.

6 files changed, 1081 insertions, 1 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d88dce2e56b..b0d3a307b72 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2006-03-28  Jim Blandy  <jimb@codesourcery.com>
+
+	* prologue-value.c, prologue-value.h: New files.
+	* Makefile.in (prologue_value_h): New variable.
+	(HFILES_NO_SRCDIR): List prologue-value.h.
+	(SFILES): List prologue-value.c.
+	(COMMON_OBS): List prologue-value.o.
+	(prologue-value.o): New rule.
+
 2006-03-27  Michael Snyder  <msnyder@redhat.com>
 
 	* xstormy16-tdep.c (xstormy16_return_value, xstormy16_push_dummy_call,
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 1ad9738eef5..ba418186e46 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -542,6 +542,7 @@ SFILES = ada-exp.y ada-lang.c ada-typeprint.c ada-valprint.c  \
 	objc-exp.y objc-lang.c \
 	objfiles.c osabi.c observer.c \
 	p-exp.y p-lang.c p-typeprint.c p-valprint.c parse.c printcmd.c \
+	prologue-value.c \
 	regcache.c reggroups.c remote.c remote-fileio.c \
 	scm-exp.c scm-lang.c scm-valprint.c \
 	sentinel-frame.c \
@@ -757,6 +758,7 @@ ppcnbsd_tdep_h = ppcnbsd-tdep.h
 ppcobsd_tdep_h = ppcobsd-tdep.h
 ppc_tdep_h = ppc-tdep.h
 proc_utils_h = proc-utils.h
+prologue_value_h = prologue-value.h
 regcache_h = regcache.h
 reggroups_h = reggroups.h
 regset_h = regset.h
@@ -867,6 +869,7 @@ HFILES_NO_SRCDIR = bcache.h buildsym.h call-cmds.h coff-solib.h defs.h \
 	symfile.h stabsread.h target.h terminal.h typeprint.h \
 	xcoffsolib.h \
 	macrotab.h macroexp.h macroscope.h \
+	prologue-value.h \
 	ada-lang.h c-lang.h f-lang.h \
 	jv-lang.h \
 	m2-lang.h  p-lang.h \
@@ -2437,6 +2440,8 @@ procfs.o: procfs.c $(defs_h) $(inferior_h) $(target_h) $(gdbcore_h) \
 proc-service.o: proc-service.c $(defs_h) $(gdb_proc_service_h) $(inferior_h) \
 	$(symtab_h) $(target_h) $(gregset_h)
 proc-why.o: proc-why.c $(defs_h) $(proc_utils_h)
+prologue-value.o: prologue-value.c $(defs_h) $(gdb_string_h) $(gdb_assert_h) \
+	$(prologue_value_h) $(regcache_h)
 p-typeprint.o: p-typeprint.c $(defs_h) $(gdb_obstack_h) $(bfd_h) $(symtab_h) \
 	$(gdbtypes_h) $(expression_h) $(value_h) $(gdbcore_h) $(target_h) \
 	$(language_h) $(p_lang_h) $(typeprint_h) $(gdb_string_h)
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 6345276ed4c..5af047593d9 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2006-03-28  Jim Blandy  <jimb@codesourcery.com>
+
+	* gdbint.texinfo (Prologue Analysis): New section.
+
 2006-03-07  Jim Blandy  <jimb@red-bean.com>
 
 	* gdb.texinfo (Connecting): Document 'target remote pipe'.
diff --git a/gdb/doc/gdbint.texinfo b/gdb/doc/gdbint.texinfo
index de3ccaae4db..2d646b8c281 100644
--- a/gdb/doc/gdbint.texinfo
+++ b/gdb/doc/gdbint.texinfo
@@ -39,7 +39,7 @@ Free Documentation License''.
 @page
 @tex
 \def\$#1${{#1}}  % Kluge: collect RCS revision info without $...$
-\xdef\manvers{\$Revision: 1.239 $}  % For use in headers, footers too
+\xdef\manvers{\$Revision: 1.240 $}  % For use in headers, footers too
 {\parskip=0pt
 \hfill Cygnus Solutions\par
 \hfill \manvers\par
@@ -287,6 +287,175 @@ used to create a new @value{GDBN} frame struct, and then
 @code{DEPRECATED_INIT_EXTRA_FRAME_INFO} and
 @code{DEPRECATED_INIT_FRAME_PC} will be called for the new frame.
 
+@section Prologue Analysis
+
+@cindex prologue analysis
+@cindex call frame information
+@cindex CFI (call frame information)
+To produce a backtrace and allow the user to manipulate older frames'
+variables and arguments, @value{GDBN} needs to find the base addresses
+of older frames, and discover where those frames' registers have been
+saved.  Since a frame's ``callee-saves'' registers get saved by
+younger frames if and when they're reused, a frame's registers may be
+scattered unpredictably across younger frames.  This means that
+changing the value of a register-allocated variable in an older frame
+may actually entail writing to a save slot in some younger frame.
+
+Modern versions of GCC emit Dwarf call frame information (``CFI''),
+which describes how to find frame base addresses and saved registers.
+But CFI is not always available, so as a fallback @value{GDBN} uses a
+technique called @dfn{prologue analysis} to find frame sizes and saved
+registers.  A prologue analyzer disassembles the function's machine
+code starting from its entry point, and looks for instructions that
+allocate frame space, save the stack pointer in a frame pointer
+register, save registers, and so on.  Obviously, this can't be done
+accurately in general, but it's tractible to do well enough to be very
+helpful.  Prologue analysis predates the GNU toolchain's support for
+CFI; at one time, prologue analysis was the only mechanism
+@value{GDBN} used for stack unwinding at all, when the function
+calling conventions didn't specify a fixed frame layout.
+
+In the olden days, function prologues were generated by hand-written,
+target-specific code in GCC, and treated as opaque and untouchable by
+optimizers.  Looking at this code, it was usually straightforward to
+write a prologue analyzer for @value{GDBN} that would accurately
+understand all the prologues GCC would generate.  However, over time
+GCC became more aggressive about instruction scheduling, and began to
+understand more about the semantics of the prologue instructions
+themselves; in response, @value{GDBN}'s analyzers became more complex
+and fragile.  Keeping the prologue analyzers working as GCC (and the
+instruction sets themselves) evolved became a substantial task.
+
+@cindex @file{prologue-value.c}
+@cindex abstract interpretation of function prologues
+@cindex pseudo-evaluation of function prologues
+To try to address this problem, the code in @file{prologue-value.h}
+and @file{prologue-value.c} provides a general framework for writing
+prologue analyzers that are simpler and more robust than ad-hoc
+analyzers.  When we analyze a prologue using the prologue-value
+framework, we're really doing ``abstract interpretation'' or
+``pseudo-evaluation'': running the function's code in simulation, but
+using conservative approximations of the values registers and memory
+would hold when the code actually runs.  For example, if our function
+starts with the instruction:
+
+@example
+addi r1, 42     # add 42 to r1
+@end example
+@noindent
+we don't know exactly what value will be in @code{r1} after executing
+this instruction, but we do know it'll be 42 greater than its original
+value.
+
+If we then see an instruction like:
+
+@example
+addi r1, 22     # add 22 to r1
+@end example
+@noindent
+we still don't know what @code{r1's} value is, but again, we can say
+it is now 64 greater than its original value.
+
+If the next instruction were:
+
+@example
+mov r2, r1      # set r2 to r1's value
+@end example
+@noindent
+then we can say that @code{r2's} value is now the original value of
+@code{r1} plus 64.
+
+It's common for prologues to save registers on the stack, so we'll
+need to track the values of stack frame slots, as well as the
+registers.  So after an instruction like this:
+
+@example
+mov (fp+4), r2
+@end example
+@noindent
+then we'd know that the stack slot four bytes above the frame pointer
+holds the original value of @code{r1} plus 64.
+
+And so on.
+
+Of course, this can only go so far before it gets unreasonable.  If we
+wanted to be able to say anything about the value of @code{r1} after
+the instruction:
+
+@example
+xor r1, r3      # exclusive-or r1 and r3, place result in r1
+@end example
+@noindent
+then things would get pretty complex.  But remember, we're just doing
+a conservative approximation; if exclusive-or instructions aren't
+relevant to prologues, we can just say @code{r1}'s value is now
+``unknown''.  We can ignore things that are too complex, if that loss of
+information is acceptable for our application.
+
+So when we say ``conservative approximation'' here, what we mean is an
+approximation that is either accurate, or marked ``unknown'', but
+never inaccurate.
+
+Using this framework, a prologue analyzer is simply an interpreter for
+machine code, but one that uses conservative approximations for the
+contents of registers and memory instead of actual values.  Starting
+from the function's entry point, you simulate instructions up to the
+current PC, or an instruction that you don't know how to simulate.
+Now you can examine the state of the registers and stack slots you've
+kept track of.
+
+@itemize @bullet
+
+@item
+To see how large your stack frame is, just check the value of the
+stack pointer register; if it's the original value of the SP
+minus a constant, then that constant is the stack frame's size.
+If the SP's value has been marked as ``unknown'', then that means
+the prologue has done something too complex for us to track, and
+we don't know the frame size.
+
+@item
+To see where we've saved the previous frame's registers, we just
+search the values we've tracked --- stack slots, usually, but
+registers, too, if you want --- for something equal to the register's
+original value.  If the calling conventions suggest a standard place
+to save a given register, then we can check there first, but really,
+anything that will get us back the original value will probably work.
+@end itemize
+
+This does take some work.  But prologue analyzers aren't
+quick-and-simple pattern patching to recognize a few fixed prologue
+forms any more; they're big, hairy functions.  Along with inferior
+function calls, prologue analysis accounts for a substantial portion
+of the time needed to stabilize a @value{GDBN} port.  So it's
+worthwhile to look for an approach that will be easier to understand
+and maintain.  In the approach described above:
+
+@itemize @bullet
+
+@item
+It's easier to see that the analyzer is correct: you just see
+whether the analyzer properly (albiet conservatively) simulates
+the effect of each instruction.
+
+@item
+It's easier to extend the analyzer: you can add support for new
+instructions, and know that you haven't broken anything that
+wasn't already broken before.
+
+@item
+It's orthogonal: to gather new information, you don't need to
+complicate the code for each instruction.  As long as your domain
+of conservative values is already detailed enough to tell you
+what you need, then all the existing instruction simulations are
+already gathering the right data for you.
+
+@end itemize
+
+The file @file{prologue-value.h} contains detailed comments explaining
+the framework and how to use it.
+
+
 @section Breakpoint Handling
 
 @cindex breakpoints
diff --git a/gdb/prologue-value.c b/gdb/prologue-value.c
new file mode 100644
index 00000000000..4ad4d6c828f
--- /dev/null
+++ b/gdb/prologue-value.c
@@ -0,0 +1,591 @@
+/* Prologue value handling for GDB.
+   Copyright 2003, 2004, 2005 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to:
+
+        Free Software Foundation, Inc.
+        51 Franklin St - Fifth Floor
+        Boston, MA 02110-1301
+        USA */
+
+#include "defs.h"
+#include "gdb_string.h"
+#include "gdb_assert.h"
+#include "prologue-value.h"
+#include "regcache.h"
+
+
+/* Constructors.  */
+
+pv_t
+pv_unknown (void)
+{
+  pv_t v = { pvk_unknown, 0, 0 };
+
+  return v;
+}
+
+
+pv_t
+pv_constant (CORE_ADDR k)
+{
+  pv_t v;
+
+  v.kind = pvk_constant;
+  v.reg = -1;                   /* for debugging */
+  v.k = k;
+
+  return v;
+}
+
+
+pv_t
+pv_register (int reg, CORE_ADDR k)
+{
+  pv_t v;
+
+  v.kind = pvk_register;
+  v.reg = reg;
+  v.k = k;
+
+  return v;
+}
+
+
+
+/* Arithmetic operations.  */
+
+/* If one of *A and *B is a constant, and the other isn't, swap the
+   values as necessary to ensure that *B is the constant.  This can
+   reduce the number of cases we need to analyze in the functions
+   below.  */
+static void
+constant_last (pv_t *a, pv_t *b)
+{
+  if (a->kind == pvk_constant
+      && b->kind != pvk_constant)
+    {
+      pv_t temp = *a;
+      *a = *b;
+      *b = temp;
+    }
+}
+
+
+pv_t
+pv_add (pv_t a, pv_t b)
+{
+  constant_last (&a, &b);
+
+  /* We can add a constant to a register.  */
+  if (a.kind == pvk_register
+      && b.kind == pvk_constant)
+    return pv_register (a.reg, a.k + b.k);
+
+  /* We can add a constant to another constant.  */
+  else if (a.kind == pvk_constant
+           && b.kind == pvk_constant)
+    return pv_constant (a.k + b.k);
+
+  /* Anything else we don't know how to add.  We don't have a
+     representation for, say, the sum of two registers, or a multiple
+     of a register's value (adding a register to itself).  */
+  else
+    return pv_unknown ();
+}
+
+
+pv_t
+pv_add_constant (pv_t v, CORE_ADDR k)
+{
+  /* Rather than thinking of all the cases we can and can't handle,
+     we'll just let pv_add take care of that for us.  */
+  return pv_add (v, pv_constant (k));
+}
+
+
+pv_t
+pv_subtract (pv_t a, pv_t b)
+{
+  /* This isn't quite the same as negating B and adding it to A, since
+     we don't have a representation for the negation of anything but a
+     constant.  For example, we can't negate { pvk_register, R1, 10 },
+     but we do know that { pvk_register, R1, 10 } minus { pvk_register,
+     R1, 5 } is { pvk_constant, <ignored>, 5 }.
+
+     This means, for example, that we could subtract two stack
+     addresses; they're both relative to the original SP.  Since the
+     frame pointer is set based on the SP, its value will be the
+     original SP plus some constant (probably zero), so we can use its
+     value just fine, too.  */
+
+  constant_last (&a, &b);
+
+  /* We can subtract two constants.  */
+  if (a.kind == pvk_constant
+      && b.kind == pvk_constant)
+    return pv_constant (a.k - b.k);
+
+  /* We can subtract a constant from a register.  */
+  else if (a.kind == pvk_register
+           && b.kind == pvk_constant)
+    return pv_register (a.reg, a.k - b.k);
+
+  /* We can subtract a register from itself, yielding a constant.  */
+  else if (a.kind == pvk_register
+           && b.kind == pvk_register
+           && a.reg == b.reg)
+    return pv_constant (a.k - b.k);
+
+  /* We don't know how to subtract anything else.  */
+  else
+    return pv_unknown ();
+}
+
+
+pv_t
+pv_logical_and (pv_t a, pv_t b)
+{
+  constant_last (&a, &b);
+
+  /* We can 'and' two constants.  */
+  if (a.kind == pvk_constant
+      && b.kind == pvk_constant)
+    return pv_constant (a.k & b.k);
+
+  /* We can 'and' anything with the constant zero.  */
+  else if (b.kind == pvk_constant
+           && b.k == 0)
+    return pv_constant (0);
+
+  /* We can 'and' anything with ~0.  */
+  else if (b.kind == pvk_constant
+           && b.k == ~ (CORE_ADDR) 0)
+    return a;
+
+  /* We can 'and' a register with itself.  */
+  else if (a.kind == pvk_register
+           && b.kind == pvk_register
+           && a.reg == b.reg
+           && a.k == b.k)
+    return a;
+
+  /* Otherwise, we don't know.  */
+  else
+    return pv_unknown ();
+}
+
+
+
+/* Examining prologue values.  */
+
+int
+pv_is_identical (pv_t a, pv_t b)
+{
+  if (a.kind != b.kind)
+    return 0;
+
+  switch (a.kind)
+    {
+    case pvk_unknown:
+      return 1;
+    case pvk_constant:
+      return (a.k == b.k);
+    case pvk_register:
+      return (a.reg == b.reg && a.k == b.k);
+    default:
+      gdb_assert (0);
+    }
+}
+
+
+int
+pv_is_constant (pv_t a)
+{
+  return (a.kind == pvk_constant);
+}
+
+
+int
+pv_is_register (pv_t a, int r)
+{
+  return (a.kind == pvk_register
+          && a.reg == r);
+}
+
+
+int
+pv_is_register_k (pv_t a, int r, CORE_ADDR k)
+{
+  return (a.kind == pvk_register
+          && a.reg == r
+          && a.k == k);
+}
+
+
+enum pv_boolean
+pv_is_array_ref (pv_t addr, CORE_ADDR size,
+                 pv_t array_addr, CORE_ADDR array_len,
+                 CORE_ADDR elt_size,
+                 int *i)
+{
+  /* Note that, since .k is a CORE_ADDR, and CORE_ADDR is unsigned, if
+     addr is *before* the start of the array, then this isn't going to
+     be negative...  */
+  pv_t offset = pv_subtract (addr, array_addr);
+
+  if (offset.kind == pvk_constant)
+    {
+      /* This is a rather odd test.  We want to know if the SIZE bytes
+         at ADDR don't overlap the array at all, so you'd expect it to
+         be an || expression: "if we're completely before || we're
+         completely after".  But with unsigned arithmetic, things are
+         different: since it's a number circle, not a number line, the
+         right values for offset.k are actually one contiguous range.  */
+      if (offset.k <= -size
+          && offset.k >= array_len * elt_size)
+        return pv_definite_no;
+      else if (offset.k % elt_size != 0
+               || size != elt_size)
+        return pv_maybe;
+      else
+        {
+          *i = offset.k / elt_size;
+          return pv_definite_yes;
+        }
+    }
+  else
+    return pv_maybe;
+}
+
+
+
+/* Areas.  */
+
+
+/* A particular value known to be stored in an area.
+
+   Entries form a ring, sorted by unsigned offset from the area's base
+   register's value.  Since entries can straddle the wrap-around point,
+   unsigned offsets form a circle, not a number line, so the list
+   itself is structured the same way --- there is no inherent head.
+   The entry with the lowest offset simply follows the entry with the
+   highest offset.  Entries may abut, but never overlap.  The area's
+   'entry' pointer points to an arbitrary node in the ring.  */
+struct area_entry
+{
+  /* Links in the doubly-linked ring.  */
+  struct area_entry *prev, *next;
+
+  /* Offset of this entry's address from the value of the base
+     register.  */
+  CORE_ADDR offset;
+
+  /* The size of this entry.  Note that an entry may wrap around from
+     the end of the address space to the beginning.  */
+  CORE_ADDR size;
+
+  /* The value stored here.  */
+  pv_t value;
+};
+
+
+struct pv_area
+{
+  /* This area's base register.  */
+  int base_reg;
+
+  /* The mask to apply to addresses, to make the wrap-around happen at
+     the right place.  */
+  CORE_ADDR addr_mask;
+
+  /* An element of the doubly-linked ring of entries, or zero if we
+     have none.  */
+  struct area_entry *entry;
+};
+
+
+struct pv_area *
+make_pv_area (int base_reg)
+{
+  struct pv_area *a = (struct pv_area *) xmalloc (sizeof (*a));
+
+  memset (a, 0, sizeof (*a));
+
+  a->base_reg = base_reg;
+  a->entry = 0;
+
+  /* Remember that shift amounts equal to the type's width are
+     undefined.  */
+  a->addr_mask = ((((CORE_ADDR) 1 << (TARGET_ADDR_BIT - 1)) - 1) << 1) | 1;
+
+  return a;
+}
+
+
+/* Delete all entries from AREA.  */
+static void
+clear_entries (struct pv_area *area)
+{
+  struct area_entry *e = area->entry;
+
+  if (e)
+    {
+      /* This needs to be a do-while loop, in order to actually
+         process the node being checked for in the terminating
+         condition.  */
+      do
+        {
+          struct area_entry *next = e->next;
+          xfree (e);
+        }
+      while (e != area->entry);
+
+      area->entry = 0;
+    }
+}
+
+
+void
+free_pv_area (struct pv_area *area)
+{
+  clear_entries (area);
+  xfree (area);
+}
+
+
+static void
+do_free_pv_area_cleanup (void *arg)
+{
+  free_pv_area ((struct pv_area *) arg);
+}
+
+
+struct cleanup *
+make_cleanup_free_pv_area (struct pv_area *area)
+{
+  return make_cleanup (do_free_pv_area_cleanup, (void *) area);
+}
+
+
+int
+pv_area_store_would_trash (struct pv_area *area, pv_t addr)
+{
+  /* It may seem odd that pvk_constant appears here --- after all,
+     that's the case where we know the most about the address!  But
+     pv_areas are always relative to a register, and we don't know the
+     value of the register, so we can't compare entry addresses to
+     constants.  */
+  return (addr.kind == pvk_unknown
+          || addr.kind == pvk_constant
+          || (addr.kind == pvk_register && addr.reg != area->base_reg));
+}
+
+
+/* Return a pointer to the first entry we hit in AREA starting at
+   OFFSET and going forward.
+
+   This may return zero, if AREA has no entries.
+
+   And since the entries are a ring, this may return an entry that
+   entirely preceeds OFFSET.  This is the correct behavior: depending
+   on the sizes involved, we could still overlap such an area, with
+   wrap-around.  */
+static struct area_entry *
+find_entry (struct pv_area *area, CORE_ADDR offset)
+{
+  struct area_entry *e = area->entry;
+
+  if (! e)
+    return 0;
+
+  /* If the next entry would be better than the current one, then scan
+     forward.  Since we use '<' in this loop, it always terminates.
+
+     Note that, even setting aside the addr_mask stuff, we must not
+     simplify this, in high school algebra fashion, to
+     (e->next->offset < e->offset), because of the way < interacts
+     with wrap-around.  We have to subtract offset from both sides to
+     make sure both things we're comparing are on the same side of the
+     discontinuity.  */
+  while (((e->next->offset - offset) & area->addr_mask)
+         < ((e->offset - offset) & area->addr_mask))
+    e = e->next;
+
+  /* If the previous entry would be better than the current one, then
+     scan backwards.  */
+  while (((e->prev->offset - offset) & area->addr_mask)
+         < ((e->offset - offset) & area->addr_mask))
+    e = e->prev;
+
+  /* In case there's some locality to the searches, set the area's
+     pointer to the entry we've found.  */
+  area->entry = e;
+
+  return e;
+}
+
+
+/* Return non-zero if the SIZE bytes at OFFSET would overlap ENTRY;
+   return zero otherwise.  AREA is the area to which ENTRY belongs.  */
+static int
+overlaps (struct pv_area *area,
+          struct area_entry *entry,
+          CORE_ADDR offset,
+          CORE_ADDR size)
+{
+  /* Think carefully about wrap-around before simplifying this.  */
+  return (((entry->offset - offset) & area->addr_mask) < size
+          || ((offset - entry->offset) & area->addr_mask) < entry->size);
+}
+
+
+void
+pv_area_store (struct pv_area *area,
+               pv_t addr,
+               CORE_ADDR size,
+               pv_t value)
+{
+  /* Remove any (potentially) overlapping entries.  */
+  if (pv_area_store_would_trash (area, addr))
+    clear_entries (area);
+  else
+    {
+      CORE_ADDR offset = addr.k;
+      struct area_entry *e = find_entry (area, offset);
+
+      /* Delete all entries that we would overlap.  */
+      while (e && overlaps (area, e, offset, size))
+        {
+          struct area_entry *next = (e->next == e) ? 0 : e->next;
+          e->prev->next = e->next;
+          e->next->prev = e->prev;
+
+          xfree (e);
+          e = next;
+        }
+
+      /* Move the area's pointer to the next remaining entry.  This
+         will also zero the pointer if we've deleted all the entries.  */
+      area->entry = e;
+    }
+
+  /* Now, there are no entries overlapping us, and area->entry is
+     either zero or pointing at the closest entry after us.  We can
+     just insert ourselves before that.
+
+     But if we're storing an unknown value, don't bother --- that's
+     the default.  */
+  if (value.kind == pvk_unknown)
+    return;
+  else
+    {
+      CORE_ADDR offset = addr.k;
+      struct area_entry *e = (struct area_entry *) xmalloc (sizeof (*e));
+      e->offset = offset;
+      e->size = size;
+      e->value = value;
+
+      if (area->entry)
+        {
+          e->prev = area->entry->prev;
+          e->next = area->entry;
+          e->prev->next = e->next->prev = e;
+        }
+      else
+        {
+          e->prev = e->next = e;
+          area->entry = e;
+        }
+    }
+}
+
+
+pv_t
+pv_area_fetch (struct pv_area *area, pv_t addr, CORE_ADDR size)
+{
+  /* If we have no entries, or we can't decide how ADDR relates to the
+     entries we do have, then the value is unknown.  */
+  if (! area->entry
+      || pv_area_store_would_trash (area, addr))
+    return pv_unknown ();
+  else
+    {
+      CORE_ADDR offset = addr.k;
+      struct area_entry *e = find_entry (area, offset);
+
+      /* If this entry exactly matches what we're looking for, then
+         we're set.  Otherwise, say it's unknown.  */
+      if (e->offset == offset && e->size == size)
+        return e->value;
+      else
+        return pv_unknown ();
+    }
+}
+
+
+int
+pv_area_find_reg (struct pv_area *area,
+                  struct gdbarch *gdbarch,
+                  int reg,
+                  CORE_ADDR *offset_p)
+{
+  struct area_entry *e = area->entry;
+
+  if (e)
+    do
+      {
+        if (e->value.kind == pvk_register
+            && e->value.reg == reg
+            && e->value.k == 0
+            && e->size == register_size (gdbarch, reg))
+          {
+            if (offset_p)
+              *offset_p = e->offset;
+            return 1;
+          }
+
+        e = e->next;
+      }
+    while (e != area->entry);
+
+  return 0;
+}
+
+
+void
+pv_area_scan (struct pv_area *area,
+              void (*func) (void *closure,
+                            pv_t addr,
+                            CORE_ADDR size,
+                            pv_t value),
+              void *closure)
+{
+  struct area_entry *e = area->entry;
+  pv_t addr;
+
+  addr.kind = pvk_register;
+  addr.reg = area->base_reg;
+
+  if (e)
+    do
+      {
+        addr.k = e->offset;
+        func (closure, addr, e->size, e->value);
+        e = e->next;
+      }
+    while (e != area->entry);
+}
diff --git a/gdb/prologue-value.h b/gdb/prologue-value.h
new file mode 100644
index 00000000000..ec44cad021f
--- /dev/null
+++ b/gdb/prologue-value.h
@@ -0,0 +1,302 @@
+/* Interface to prologue value handling for GDB.
+   Copyright 2003, 2004, 2005 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to:
+
+        Free Software Foundation, Inc.
+        51 Franklin St - Fifth Floor
+        Boston, MA 02110-1301
+        USA */
+
+#ifndef PROLOGUE_VALUE_H
+#define PROLOGUE_VALUE_H
+
+/* When we analyze a prologue, we're really doing 'abstract
+   interpretation' or 'pseudo-evaluation': running the function's code
+   in simulation, but using conservative approximations of the values
+   it would have when it actually runs.  For example, if our function
+   starts with the instruction:
+
+      addi r1, 42     # add 42 to r1
+
+   we don't know exactly what value will be in r1 after executing this
+   instruction, but we do know it'll be 42 greater than its original
+   value.
+
+   If we then see an instruction like:
+
+      addi r1, 22     # add 22 to r1
+
+   we still don't know what r1's value is, but again, we can say it is
+   now 64 greater than its original value.
+
+   If the next instruction were:
+
+      mov r2, r1      # set r2 to r1's value
+
+   then we can say that r2's value is now the original value of r1
+   plus 64.
+
+   It's common for prologues to save registers on the stack, so we'll
+   need to track the values of stack frame slots, as well as the
+   registers.  So after an instruction like this:
+
+      mov (fp+4), r2
+
+   then we'd know that the stack slot four bytes above the frame
+   pointer holds the original value of r1 plus 64.
+
+   And so on.
+
+   Of course, this can only go so far before it gets unreasonable.  If
+   we wanted to be able to say anything about the value of r1 after
+   the instruction:
+
+      xor r1, r3      # exclusive-or r1 and r3, place result in r1
+
+   then things would get pretty complex.  But remember, we're just
+   doing a conservative approximation; if exclusive-or instructions
+   aren't relevant to prologues, we can just say r1's value is now
+   'unknown'.  We can ignore things that are too complex, if that loss
+   of information is acceptable for our application.
+
+   So when I say "conservative approximation" here, what I mean is an
+   approximation that is either accurate, or marked "unknown", but
+   never inaccurate.
+
+   Once you've reached the current PC, or an instruction that you
+   don't know how to simulate, you stop.  Now you can examine the
+   state of the registers and stack slots you've kept track of.
+
+   - To see how large your stack frame is, just check the value of the
+     stack pointer register; if it's the original value of the SP
+     minus a constant, then that constant is the stack frame's size.
+     If the SP's value has been marked as 'unknown', then that means
+     the prologue has done something too complex for us to track, and
+     we don't know the frame size.
+
+   - To see where we've saved the previous frame's registers, we just
+     search the values we've tracked --- stack slots, usually, but
+     registers, too, if you want --- for something equal to the
+     register's original value.  If the ABI suggests a standard place
+     to save a given register, then we can check there first, but
+     really, anything that will get us back the original value will
+     probably work.
+
+   Sure, this takes some work.  But prologue analyzers aren't
+   quick-and-simple pattern patching to recognize a few fixed prologue
+   forms any more; they're big, hairy functions.  Along with inferior
+   function calls, prologue analysis accounts for a substantial
+   portion of the time needed to stabilize a GDB port.  So I think
+   it's worthwhile to look for an approach that will be easier to
+   understand and maintain.  In the approach used here:
+
+   - It's easier to see that the analyzer is correct: you just see
+     whether the analyzer properly (albiet conservatively) simulates
+     the effect of each instruction.
+
+   - It's easier to extend the analyzer: you can add support for new
+     instructions, and know that you haven't broken anything that
+     wasn't already broken before.
+
+   - It's orthogonal: to gather new information, you don't need to
+     complicate the code for each instruction.  As long as your domain
+     of conservative values is already detailed enough to tell you
+     what you need, then all the existing instruction simulations are
+     already gathering the right data for you.
+
+   A 'struct prologue_value' is a conservative approximation of the
+   real value the register or stack slot will have.  */
+
+struct prologue_value {
+
+  /* What sort of value is this?  This determines the interpretation
+     of subsequent fields.  */
+  enum {
+
+    /* We don't know anything about the value.  This is also used for
+       values we could have kept track of, when doing so would have
+       been too complex and we don't want to bother.  The bottom of
+       our lattice.  */
+    pvk_unknown,
+
+    /* A known constant.  K is its value.  */
+    pvk_constant,
+
+    /* The value that register REG originally had *UPON ENTRY TO THE
+       FUNCTION*, plus K.  If K is zero, this means, obviously, just
+       the value REG had upon entry to the function.  REG is a GDB
+       register number.  Before we start interpreting, we initialize
+       every register R to { pvk_register, R, 0 }.  */
+    pvk_register,
+
+  } kind;
+
+  /* The meanings of the following fields depend on 'kind'; see the
+     comments for the specific 'kind' values.  */
+  int reg;
+  CORE_ADDR k;
+};
+
+typedef struct prologue_value pv_t;
+
+
+/* Return the unknown prologue value --- { pvk_unknown, ?, ? }.  */
+pv_t pv_unknown (void);
+
+/* Return the prologue value representing the constant K.  */
+pv_t pv_constant (CORE_ADDR k);
+
+/* Return the prologue value representing the original value of
+   register REG, plus the constant K.  */
+pv_t pv_register (int reg, CORE_ADDR k);
+
+
+/* Return conservative approximations of the results of the following
+   operations.  */
+pv_t pv_add (pv_t a, pv_t b);               /* a + b */
+pv_t pv_add_constant (pv_t v, CORE_ADDR k); /* a + k */
+pv_t pv_subtract (pv_t a, pv_t b);          /* a - b */
+pv_t pv_logical_and (pv_t a, pv_t b);       /* a & b */
+
+
+/* Return non-zero iff A and B are identical expressions.
+
+   This is not the same as asking if the two values are equal; the
+   result of such a comparison would have to be a pv_boolean, and
+   asking whether two 'unknown' values were equal would give you
+   pv_maybe.  Same for comparing, say, { pvk_register, R1, 0 } and {
+   pvk_register, R2, 0}.
+
+   Instead, this function asks whether the two representations are the
+   same.  */
+int pv_is_identical (pv_t a, pv_t b);
+
+
+/* Return non-zero if A is known to be a constant.  */
+int pv_is_constant (pv_t a);
+
+/* Return non-zero if A is the original value of register number R
+   plus some constant, zero otherwise.  */
+int pv_is_register (pv_t a, int r);
+
+
+/* Return non-zero if A is the original value of register R plus the
+   constant K.  */
+int pv_is_register_k (pv_t a, int r, CORE_ADDR k);
+
+/* A conservative boolean type, including "maybe", when we can't
+   figure out whether something is true or not.  */
+enum pv_boolean {
+  pv_maybe,
+  pv_definite_yes,
+  pv_definite_no,
+};
+
+
+/* Decide whether a reference to SIZE bytes at ADDR refers exactly to
+   an element of an array.  The array starts at ARRAY_ADDR, and has
+   ARRAY_LEN values of ELT_SIZE bytes each.  If ADDR definitely does
+   refer to an array element, set *I to the index of the referenced
+   element in the array, and return pv_definite_yes.  If it definitely
+   doesn't, return pv_definite_no.  If we can't tell, return pv_maybe.
+
+   If the reference does touch the array, but doesn't fall exactly on
+   an element boundary, or doesn't refer to the whole element, return
+   pv_maybe.  */
+enum pv_boolean pv_is_array_ref (pv_t addr, CORE_ADDR size,
+                                 pv_t array_addr, CORE_ADDR array_len,
+                                 CORE_ADDR elt_size,
+                                 int *i);
+
+
+/* A 'struct pv_area' keeps track of values stored in a particular
+   region of memory.  */
+struct pv_area;
+
+/* Create a new area, tracking stores relative to the original value
+   of BASE_REG.  If BASE_REG is SP, then this effectively records the
+   contents of the stack frame: the original value of the SP is the
+   frame's CFA, or some constant offset from it.
+
+   Stores to constant addresses, unknown addresses, or to addresses
+   relative to registers other than BASE_REG will trash this area; see
+   pv_area_store_would_trash.  */
+struct pv_area *make_pv_area (int base_reg);
+
+/* Free AREA.  */
+void free_pv_area (struct pv_area *area);
+
+
+/* Register a cleanup to free AREA.  */
+struct cleanup *make_cleanup_free_pv_area (struct pv_area *area);
+
+
+/* Store the SIZE-byte value VALUE at ADDR in AREA.
+
+   If ADDR is not relative to the same base register we used in
+   creating AREA, then we can't tell which values here the stored
+   value might overlap, and we'll have to mark everything as
+   unknown.  */
+void pv_area_store (struct pv_area *area,
+                    pv_t addr,
+                    CORE_ADDR size,
+                    pv_t value);
+
+/* Return the SIZE-byte value at ADDR in AREA.  This may return
+   pv_unknown ().  */
+pv_t pv_area_fetch (struct pv_area *area, pv_t addr, CORE_ADDR size);
+
+/* Return true if storing to address ADDR in AREA would force us to
+   mark the contents of the entire area as unknown.  This could happen
+   if, say, ADDR is unknown, since we could be storing anywhere.  Or,
+   it could happen if ADDR is relative to a different register than
+   the other stores base register, since we don't know the relative
+   values of the two registers.
+
+   If you've reached such a store, it may be better to simply stop the
+   prologue analysis, and return the information you've gathered,
+   instead of losing all that information, most of which is probably
+   okay.  */
+int pv_area_store_would_trash (struct pv_area *area, pv_t addr);
+
+
+/* Search AREA for the original value of REGISTER.  If we can't find
+   it, return zero; if we can find it, return a non-zero value, and if
+   OFFSET_P is non-zero, set *OFFSET_P to the register's offset within
+   AREA.  GDBARCH is the architecture of which REGISTER is a member.
+
+   In the worst case, this takes time proportional to the number of
+   items stored in AREA.  If you plan to gather a lot of information
+   about registers saved in AREA, consider calling pv_area_scan
+   instead, and collecting all your information in one pass.  */
+int pv_area_find_reg (struct pv_area *area,
+                      struct gdbarch *gdbarch,
+                      int register,
+                      CORE_ADDR *offset_p);
+
+
+/* For every part of AREA whose value we know, apply FUNC to CLOSURE,
+   the value's address, its size, and the value itself.  */
+void pv_area_scan (struct pv_area *area,
+                   void (*func) (void *closure,
+                                 pv_t addr,
+                                 CORE_ADDR size,
+                                 pv_t value),
+                   void *closure);
+
+
+#endif /* PROLOGUE_VALUE_H */