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 #include "frame.h"              /* For enum frame_type.  */
  32
  33 /* Return the frame unwind methods for the function that contains PC,
  34    or NULL if this this unwinder can't handle this frame.  */
  35
  36 typedef const struct frame_unwind *(frame_unwind_p_ftype) (CORE_ADDR pc);
  37
  38 /* Add a frame unwinder to the list.  The predicates are polled in the
  39    order that they are appended.  The initial list contains the dummy
  40    frame's predicate.  */
  41
  42 extern void frame_unwind_append_predicate (struct gdbarch *gdbarch,
  43                                            frame_unwind_p_ftype *p);
  44
  45 /* Iterate through the list of frame unwinders until one returns an
  46    implementation.  */
  47
  48 extern const struct frame_unwind *frame_unwind_find_by_pc (struct gdbarch
  49                                                            *gdbarch,
  50                                                            CORE_ADDR pc);
  51
  52 /* The following unwind functions assume a chain of frames forming the
  53    sequence: (outer) prev <-> this <-> next (inner).  All the
  54    functions are called with called with the next frame's `struct
  55    frame_info' and and this frame's prologue cache.
  56
  57    THIS frame's register values can be obtained by unwinding NEXT
  58    frame's registers (a recursive operation).
  59
  60    THIS frame's prologue cache can be used to cache information such
  61    as where this frame's prologue stores the previous frame's
  62    registers.  */
  63
  64 /* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
  65    use the NEXT frame, and its register unwind method, to determine
  66    the frame ID of THIS frame.
  67
  68    A frame ID provides an invariant that can be used to re-identify an
  69    instance of a frame.  It is a combination of the frame's `base' and
  70    the frame's function's code address.
  71
  72    Traditionally, THIS frame's ID was determined by examining THIS
  73    frame's function's prologue, and identifying the register/offset
  74    used as THIS frame's base.
  75
  76    Example: An examination of THIS frame's prologue reveals that, on
  77    entry, it saves the PC(+12), SP(+8), and R1(+4) registers
  78    (decrementing the SP by 12).  Consequently, the frame ID's base can
  79    be determined by adding 12 to the THIS frame's stack-pointer, and
  80    the value of THIS frame's SP can be obtained by unwinding the NEXT
  81    frame's SP.
  82
  83    THIS_PROLOGUE_CACHE can be used to share any prolog analysis data
  84    with the other unwind methods.  Memory for that cache should be
  85    allocated using frame_obstack_zalloc().  */
  86
  87 typedef void (frame_this_id_ftype) (struct frame_info *next_frame,
  88                                     void **this_prologue_cache,
  89                                     struct frame_id *this_id);
  90
  91 /* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
  92    use the NEXT frame, and its register unwind method, to unwind THIS
  93    frame's registers (returning the value of the specified register
  94    REGNUM in the previous frame).
  95
  96    Traditionally, THIS frame's registers were unwound by examining
  97    THIS frame's function's prologue and identifying which registers
  98    that prolog code saved on the stack.
  99
 100    Example: An examination of THIS frame's prologue reveals that, on
 101    entry, it saves the PC(+12), SP(+8), and R1(+4) registers
 102    (decrementing the SP by 12).  Consequently, the value of the PC
 103    register in the previous frame is found in memory at SP+12, and
 104    THIS frame's SP can be obtained by unwinding the NEXT frame's SP.
 105
 106    Why not pass in THIS_FRAME?  By passing in NEXT frame and THIS
 107    cache, the supplied parameters are consistent with the sibling
 108    function THIS_ID.
 109
 110    Can the code call ``frame_register (get_prev_frame (NEXT_FRAME))''?
 111    Won't the call frame_register (THIS_FRAME) be faster?  Well,
 112    ignoring the possability that the previous frame does not yet
 113    exist, the ``frame_register (FRAME)'' function is expanded to
 114    ``frame_register_unwind (get_next_frame (FRAME)'' and hence that
 115    call will expand to ``frame_register_unwind (get_next_frame
 116    (get_prev_frame (NEXT_FRAME)))''.  Might as well call
 117    ``frame_register_unwind (NEXT_FRAME)'' directly.
 118
 119    THIS_PROLOGUE_CACHE can be used to share any prolog analysis data
 120    with the other unwind methods.  Memory for that cache should be
 121    allocated using frame_obstack_zalloc().  */
 122
 123 typedef void (frame_prev_register_ftype) (struct frame_info *next_frame,
 124                                           void **this_prologue_cache,
 125                                           int prev_regnum,
 126                                           int *optimized,
 127                                           enum lval_type * lvalp,
 128                                           CORE_ADDR *addrp,
 129                                           int *realnump, void *valuep);
 130
 131 struct frame_unwind
 132 {
 133   /* The frame's type.  Should this instead be a collection of
 134      predicates that test the frame for various attributes?  */
 135   enum frame_type type;
 136   /* Should an attribute indicating the frame's address-in-block go
 137      here?  */
 138   frame_this_id_ftype *this_id;
 139   frame_prev_register_ftype *prev_register;
 140 };
 141
 142 #endif