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 /* For compatibility with the old frame code.  See end of header for
  34    new methods.  */
  35 typedef const struct frame_unwind *(frame_unwind_p_ftype) (CORE_ADDR pc);
  36 extern void frame_unwind_append_predicate (struct gdbarch *gdbarch,
  37                                            frame_unwind_p_ftype *p);
  38
  39 /* The following unwind functions assume a chain of frames forming the
  40    sequence: (outer) prev <-> this <-> next (inner).  All the
  41    functions are called with called with the next frame's `struct
  42    frame_info' and and this frame's prologue cache.
  43
  44    THIS frame's register values can be obtained by unwinding NEXT
  45    frame's registers (a recursive operation).
  46
  47    THIS frame's prologue cache can be used to cache information such
  48    as where this frame's prologue stores the previous frame's
  49    registers.  */
  50
  51 /* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
  52    use the NEXT frame, and its register unwind method, to determine
  53    the frame ID of THIS frame.
  54
  55    A frame ID provides an invariant that can be used to re-identify an
  56    instance of a frame.  It is a combination of the frame's `base' and
  57    the frame's function's code address.
  58
  59    Traditionally, THIS frame's ID was determined by examining THIS
  60    frame's function's prologue, and identifying the register/offset
  61    used as THIS frame's base.
  62
  63    Example: An examination of THIS frame's prologue reveals that, on
  64    entry, it saves the PC(+12), SP(+8), and R1(+4) registers
  65    (decrementing the SP by 12).  Consequently, the frame ID's base can
  66    be determined by adding 12 to the THIS frame's stack-pointer, and
  67    the value of THIS frame's SP can be obtained by unwinding the NEXT
  68    frame's SP.
  69
  70    THIS_PROLOGUE_CACHE can be used to share any prolog analysis data
  71    with the other unwind methods.  Memory for that cache should be
  72    allocated using frame_obstack_zalloc().  */
  73
  74 typedef void (frame_this_id_ftype) (struct frame_info *next_frame,
  75                                     void **this_prologue_cache,
  76                                     struct frame_id *this_id);
  77
  78 /* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
  79    use the NEXT frame, and its register unwind method, to unwind THIS
  80    frame's registers (returning the value of the specified register
  81    REGNUM in the previous frame).
  82
  83    Traditionally, THIS frame's registers were unwound by examining
  84    THIS frame's function's prologue and identifying which registers
  85    that prolog code saved on the stack.
  86
  87    Example: An examination of THIS frame's prologue reveals that, on
  88    entry, it saves the PC(+12), SP(+8), and R1(+4) registers
  89    (decrementing the SP by 12).  Consequently, the value of the PC
  90    register in the previous frame is found in memory at SP+12, and
  91    THIS frame's SP can be obtained by unwinding the NEXT frame's SP.
  92
  93    Why not pass in THIS_FRAME?  By passing in NEXT frame and THIS
  94    cache, the supplied parameters are consistent with the sibling
  95    function THIS_ID.
  96
  97    Can the code call ``frame_register (get_prev_frame (NEXT_FRAME))''?
  98    Won't the call frame_register (THIS_FRAME) be faster?  Well,
  99    ignoring the possability that the previous frame does not yet
 100    exist, the ``frame_register (FRAME)'' function is expanded to
 101    ``frame_register_unwind (get_next_frame (FRAME)'' and hence that
 102    call will expand to ``frame_register_unwind (get_next_frame
 103    (get_prev_frame (NEXT_FRAME)))''.  Might as well call
 104    ``frame_register_unwind (NEXT_FRAME)'' directly.
 105
 106    THIS_PROLOGUE_CACHE can be used to share any prolog analysis data
 107    with the other unwind methods.  Memory for that cache should be
 108    allocated using frame_obstack_zalloc().  */
 109
 110 typedef void (frame_prev_register_ftype) (struct frame_info *next_frame,
 111                                           void **this_prologue_cache,
 112                                           int prev_regnum,
 113                                           int *optimized,
 114                                           enum lval_type * lvalp,
 115                                           CORE_ADDR *addrp,
 116                                           int *realnump, void *valuep);
 117
 118 struct frame_unwind
 119 {
 120   /* The frame's type.  Should this instead be a collection of
 121      predicates that test the frame for various attributes?  */
 122   enum frame_type type;
 123   /* Should an attribute indicating the frame's address-in-block go
 124      here?  */
 125   frame_this_id_ftype *this_id;
 126   frame_prev_register_ftype *prev_register;
 127 };
 128
 129 /* Given the NEXT frame, take a wiff of THIS frame's registers (namely
 130    the PC and attributes) and if it is the applicable unwinder return
 131    the unwind methods, or NULL if it is not.  */
 132
 133 typedef const struct frame_unwind *(frame_unwind_sniffer_ftype) (struct frame_info *next_frame);
 134
 135 /* Add a frame sniffer to the list.  The predicates are polled in the
 136    order that they are appended.  The initial list contains the dummy
 137    frame sniffer.  */
 138
 139 extern void frame_unwind_append_sniffer (struct gdbarch *gdbarch,
 140                                          frame_unwind_sniffer_ftype *sniffer);
 141
 142 /* Iterate through the next frame's sniffers until one returns with an
 143    unwinder implementation.  */
 144
 145 extern const struct frame_unwind *frame_unwind_find_by_frame (struct frame_info *next_frame);
 146
 147 #endif