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/* Prologue value handling for GDB.

   Copyright 2003, 2004, 2005, 2007, 2008, 2009, 2010

   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 3 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, see <http://www.gnu.org/licenses/>. */

#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, int addr_bit)

{

  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 << (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);

          e = next;

        }

      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);

}