gdb/frame-unwind.h

   1 /* Definitions for a frame unwinder, for GDB, the GNU debugger.
   2
   3    Copyright 2003 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #if !defined (FRAME_UNWIND_H)
  23 #define FRAME_UNWIND_H 1
  24
  25 struct frame_info;
  26 struct frame_id;
  27 struct frame_unwind;
  28 struct gdbarch;
  29 struct regcache;
  30
  31 /* Return the frame unwind methods for the function that contains PC,
  32    or NULL if this this unwinder can't handle this frame.  */
  33
  34 typedef const struct frame_unwind *(frame_unwind_p_ftype) (CORE_ADDR pc);
  35
  36 /* Add a frame unwinder to the list.  The predicates are polled in the
  37    order that they are appended.  The initial list contains the dummy
  38    frame's predicate.  */
  39
  40 extern void frame_unwind_append_predicate (struct gdbarch *gdbarch,
  41                                            frame_unwind_p_ftype *p);
  42
  43 /* Iterate through the list of frame unwinders until one returns an
  44    implementation.  */
  45
  46 extern const struct frame_unwind *frame_unwind_find_by_pc (struct gdbarch
  47                                                            *gdbarch,
  48                                                            CORE_ADDR pc);
  49
  50 /* The following unwind functions assume a chain of frames forming the
  51    sequence: (outer) prev <-> this <-> next (inner).  All the
  52    functions are called with called with the next frame's `struct
  53    frame_info' and and this frame's prologue cache.
  54
  55    THIS frame's register values can be obtained by unwinding NEXT
  56    frame's registers (a recursive operation).
  57
  58    THIS frame's prologue cache can be used to cache information such
  59    as where this frame's prologue stores the previous frame's
  60    registers.  */
  61
  62 /* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
  63    use the NEXT frame, and its register unwind method, to determine
  64    the frame ID of THIS frame.
  65
  66    A frame ID provides an invariant that can be used to re-identify an
  67    instance of a frame.  It is a combination of the frame's `base' and
  68    the frame's function's code address.
  69
  70    Traditionally, THIS frame's ID was determined by examining THIS
  71    frame's function's prologue, and identifying the register/offset
  72    used as THIS frame's base.
  73
  74    Example: An examination of THIS frame's prologue reveals that, on
  75    entry, it saves the PC(+12), SP(+8), and R1(+4) registers
  76    (decrementing the SP by 12).  Consequently, the frame ID's base can
  77    be determined by adding 12 to the THIS frame's stack-pointer, and
  78    the value of THIS frame's SP can be obtained by unwinding the NEXT
  79    frame's SP.
  80
  81    THIS_PROLOGUE_CACHE can be used to share any prolog analysis data
  82    with the other unwind methods.  Memory for that cache should be
  83    allocated using frame_obstack_zalloc().  */
  84
  85 typedef void (frame_this_id_ftype) (struct frame_info *next_frame,
  86                                     void **this_prologue_cache,
  87                                     struct frame_id *this_id);
  88
  89 /* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
  90    use the NEXT frame, and its register unwind method, to unwind THIS
  91    frame's registers (returning the value of the specified register
  92    REGNUM in the previous frame).
  93
  94    Traditionally, THIS frame's registers were unwound by examining
  95    THIS frame's function's prologue and identifying which registers
  96    that prolog code saved on the stack.
  97
  98    Example: An examination of THIS frame's prologue reveals that, on
  99    entry, it saves the PC(+12), SP(+8), and R1(+4) registers
 100    (decrementing the SP by 12).  Consequently, the value of the PC
 101    register in the previous frame is found in memory at SP+12, and
 102    THIS frame's SP can be obtained by unwinding the NEXT frame's SP.
 103
 104    Why not pass in THIS_FRAME?  By passing in NEXT frame and THIS
 105    cache, the supplied parameters are consistent with the sibling
 106    function THIS_ID.
 107
 108    Can the code call ``frame_register (get_prev_frame (NEXT_FRAME))''?
 109    Won't the call frame_register (THIS_FRAME) be faster?  Well,
 110    ignoring the possability that the previous frame does not yet
 111    exist, the ``frame_register (FRAME)'' function is expanded to
 112    ``frame_register_unwind (get_next_frame (FRAME)'' and hence that
 113    call will expand to ``frame_register_unwind (get_next_frame
 114    (get_prev_frame (NEXT_FRAME)))''.  Might as well call
 115    ``frame_register_unwind (NEXT_FRAME)'' directly.
 116
 117    THIS_PROLOGUE_CACHE can be used to share any prolog analysis data
 118    with the other unwind methods.  Memory for that cache should be
 119    allocated using frame_obstack_zalloc().  */
 120
 121 typedef void (frame_prev_register_ftype) (struct frame_info *next_frame,
 122                                           void **this_prologue_cache,
 123                                           int prev_regnum,
 124                                           int *optimized,
 125                                           enum lval_type * lvalp,
 126                                           CORE_ADDR *addrp,
 127                                           int *realnump, void *valuep);
 128
 129 struct frame_unwind
 130 {
 131   /* Should the frame's type go here? */
 132   /* Should an attribute indicating the frame's address-in-block go
 133      here?  */
 134   frame_this_id_ftype *this_id;
 135   frame_prev_register_ftype *prev_register;
 136 };
 137
 138 #endif