1 /****************************************************************************
3 * GNAT COMPILER COMPONENTS *
7 * C Implementation File *
9 * Copyright (C) 2000-2003 Ada Core Technologies, Inc. *
11 * GNAT is free software; you can redistribute it and/or modify it under *
12 * terms of the GNU General Public License as published by the Free Soft- *
13 * ware Foundation; either version 2, or (at your option) any later ver- *
14 * sion. GNAT is distributed in the hope that it will be useful, but WITH- *
15 * OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY *
16 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License *
17 * for more details. You should have received a copy of the GNU General *
18 * Public License distributed with GNAT; see file COPYING. If not, write *
19 * to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, *
20 * MA 02111-1307, USA. *
22 * As a special exception, if you link this file with other files to *
23 * produce an executable, this file does not by itself cause the resulting *
24 * executable to be covered by the GNU General Public License. This except- *
25 * ion does not however invalidate any other reasons why the executable *
26 * file might be covered by the GNU Public License. *
28 * GNAT was originally developed by the GNAT team at New York University. *
29 * Extensive contributions were provided by Ada Core Technologies Inc. *
31 ****************************************************************************/
33 /* This file contains low level support for stack unwinding using GCC intrinsic
35 It has been tested on the following configurations:
48 #ifdef __alpha_vxworks
61 extern int __gnat_backtrace PARAMS ((void **, int, void *, void *, int));
63 /* The point is to provide an implementation of the __gnat_bactrace function
64 above, called by the default implementation of the System.Traceback
67 We first have a series of target specific implementations, each included
68 from a separate C file for readability purposes.
70 Then comes a somewhat generic implementation based on a set of macro and
71 structure definitions which may be tailored on a per target basis. The
72 presence of a definition for one of these macros (PC_ADJUST) controls
73 wether or not the generic implementation is included.
75 Finally, there is a default dummy implementation, necessary to make the
76 linker happy on platforms where the feature is not supported, but where the
77 function is still referenced by the default System.Traceback. */
79 #define Lock_Task system__soft_links__lock_task
80 extern void (*Lock_Task) PARAMS ((void));
82 #define Unlock_Task system__soft_links__unlock_task
83 extern void (*Unlock_Task) PARAMS ((void));
85 /*-------------------------------------*
86 *-- Target specific implementations --*
87 *-------------------------------------*/
89 #if defined (__alpha_vxworks)
93 #elif defined (__ALPHA) && defined (__VMS__)
98 /* No target specific implementation. */
100 /*----------------------------------------------------------------*
101 *-- Target specific definitions for the generic implementation --*
102 *----------------------------------------------------------------*/
104 /* The stack layout is specified by the target ABI. The "generic" scheme is
105 based on the following assumption:
107 The stack layout from some frame pointer is such that the information
108 required to compute the backtrace is available at static offsets.
110 For a given frame, the information we are interested in is the saved return
111 address (somewhere after the call instruction in the caller) and a pointer
112 to the caller's frame. The former is the base of the call chain information
113 we store in the tracebacks array. The latter allows us to loop over the
114 successive frames in the chain.
116 To initiate the process, we retrieve an initial frame pointer using the
117 appropriate GCC builtin (__builtin_frame_address).
119 This scheme is unfortunately not applicable on every target because the
120 stack layout is not necessarily regular (static) enough. On targets where
121 this scheme applies, the implementation relies on the following items:
123 o struct layout, describing the expected stack data layout relevant to the
124 information we are interested in,
126 o FRAME_OFFSET, the offset, from a given frame pointer, at which this
127 layout will be found,
129 o FRAME_LEVEL, controls how many frames up we get at to start with,
130 from the initial frame pointer we compute by way of the GCC builtin,
132 0 is most often the appropriate value. 1 may be necessary on targets
133 where return addresses are saved by a function in it's caller's frame
136 o PC_ADJUST, to account for the difference between a call point (address
137 of a call instruction), which is what we want in the output array, and
138 the associated return address, which is what we retrieve from the stack.
140 o STOP_FRAME, to decide wether we reached the top of the call chain, and
141 thus if the process shall stop.
147 | | | (FRAME_OFFSET) |
148 | | | : | (PC_ADJUST)
149 | | layout:| return_address ----------------+
151 +--------------- next_frame | |
154 | +----------------+ | +-----+
155 | | : |<- Base fp | | : |
156 | | (FRAME_OFFSET) | (FRAME_LEVEL) | | : |
158 | layout:| return_address --------------------> | [0]
159 | | ... | (PC_ADJUST) +-----+
160 +---------- next_frame | traceback[]
167 Since we inherently deal with return addresses, there is an implicit shift
168 by at least one for the initial point we are able to observe in the chain.
170 On some targets (e.g. sparc-solaris), the first return address we can
171 easily get without special code is even our caller's return address, so
172 there is a initial shift of two.
174 BASE_SKIP represents this initial shift, which is the minimal "skip_frames"
175 value we support. We could add special code for the skip_frames < BASE_SKIP
176 cases. This is not done currently because there is virtually no situation
177 in which this would be useful.
179 Finally, to account for some ABI specificities, a target may (but does
182 o FORCE_CALL, to force a call to a dummy function at the very beginning
183 of the computation. See the PPC AIX target for an example where this
186 o FETCH_UP_FRAME, to force an invocation of __builtin_frame_address with a
187 positive argument right after a possibly forced call even if FRAME_LEVEL
188 is 0. See the Sparc Solaris case for an example where this is useful.
192 /*------------------------------ PPC AIX -------------------------------*/
199 void *return_address;
202 #define FRAME_OFFSET 0
204 #define STOP_FRAME(CURRENT, TOP_STACK) ((void *) (CURRENT) < (TOP_STACK))
206 /* The PPC ABI has an interesting specificity: the return address saved by a
207 function is located in it's caller's frame, and the save operation only
208 takes place if the function performs a call.
210 To have __gnat_backtrace retrieve it's own return address, we then
214 #define FRAME_LEVEL 1
218 /*---------------------------- PPC VxWorks------------------------------*/
220 #elif defined (_ARCH_PPC) && defined (__vxworks)
224 void *return_address;
228 #define FRAME_LEVEL 1
229 /* See the PPC AIX case for an explanation of these values. */
231 #define FRAME_OFFSET 0
233 #define STOP_FRAME(CURRENT, TOP_STACK) ((CURRENT)->return_address == 0)
237 /*-------------------------- Sparc Solaris -----------------------------*/
239 #elif defined (sun) && defined (sparc)
241 /* These definitions are inspired from the Appendix D (Software
242 Considerations) of the SPARC V8 architecture manual. */
247 void *return_address;
250 #define FRAME_LEVEL 0
251 #define FRAME_OFFSET (14 * (sizeof (void*)))
253 #define STOP_FRAME(CURRENT, TOP_STACK) \
254 ((CURRENT)->return_address == 0|| (CURRENT)->next == 0 \
255 || (void *) (CURRENT) < (TOP_STACK))
257 /* The sparc register windows need to be flushed before we may access them
258 from the stack. This is achieved by way of builtin_frame_address only
259 when the "count" argument is positive, so force at least one such call. */
260 #define FETCH_UP_FRAME_ADDRESS
263 /* From the frame pointer of frame N, we are accessing the flushed register
264 window of frame N-1 (positive offset from fp), in which we retrieve the
265 saved return address. We then end up with our caller's return address. */
267 /*------------------------------- x86 ----------------------------------*/
273 void *return_address;
277 /* _image_base__ is the image starting address, no stack addresses should be
279 extern unsigned int _image_base__;
280 #define LOWEST_ADDR ((unsigned int) (&_image_base__))
282 #define LOWEST_ADDR 0
285 #define FRAME_LEVEL 0
286 #define FRAME_OFFSET 0
288 #define STOP_FRAME(CURRENT, TOP_STACK) \
289 ((unsigned int)(CURRENT)->return_address < LOWEST_ADDR \
290 || (CURRENT)->return_address == 0|| (CURRENT)->next == 0 \
291 || (void *) (CURRENT) < (TOP_STACK))
295 /* On i386 architecture we check that at the call point we really have a call
296 insn. Possible call instructions are:
298 call addr16 E8 xx xx xx xx
300 call off(reg) FF xx xx
301 lcall addr seg 9A xx xx xx xx xx xx
303 This check will not catch all cases but it will increase the backtrace
304 reliability on this architecture.
307 #define VALID_STACK_FRAME(ptr) \
308 (((*((ptr) - 3) & 0xff) == 0xe8) \
309 || ((*((ptr) - 5) & 0xff) == 0x9a) \
310 || ((*((ptr) - 1) & 0xff) == 0xff) \
311 || (((*(ptr) & 0xd0ff) == 0xd0ff)))
315 /*---------------------------------------*
316 *-- The generic implementation per se --*
317 *---------------------------------------*/
319 #if defined (PC_ADJUST)
321 #ifndef CURRENT_STACK_FRAME
322 # define CURRENT_STACK_FRAME ({ char __csf; &__csf; })
326 #ifndef VALID_STACK_FRAME
327 #define VALID_STACK_FRAME(ptr) 1
330 #define MAX(x,y) ((x) > (y) ? (x) : (y))
332 /* Define a dummy function to call if FORCE_CALL is defined. Don't
333 define it otherwise, as this could lead to "defined but not used"
335 #if defined (FORCE_CALL)
336 static void forced_callee () {}
340 __gnat_backtrace (array, size, exclude_min, exclude_max, skip_frames)
347 struct layout *current;
352 /* Honor FORCE_CALL when defined. */
353 #if defined (FORCE_CALL)
357 /* Force a call to builtin_frame_address with a positive argument
358 if required. This is necessary e.g. on sparc to have the register
359 windows flushed before we attempt to access them on the stack. */
360 #if defined (FETCH_UP_FRAME_ADDRESS) && (FRAME_LEVEL == 0)
361 __builtin_frame_address (1);
364 top_frame = __builtin_frame_address (FRAME_LEVEL);
365 top_stack = CURRENT_STACK_FRAME;
366 current = (struct layout *) ((size_t) top_frame + FRAME_OFFSET);
368 /* Skip the number of calls we have been requested to skip, accounting for
369 the BASE_SKIP parameter.
371 FRAME_LEVEL is meaningless for the count adjustment. It impacts where we
372 start retrieving data from, but how many frames "up" we start at is in
373 BASE_SKIP by definition. */
375 skip_frames = MAX (0, skip_frames - BASE_SKIP);
377 while (cnt < skip_frames)
379 current = (struct layout *) ((size_t) current->next + FRAME_OFFSET);
386 if (STOP_FRAME (current, top_stack) ||
387 !VALID_STACK_FRAME((char *)(current->return_address + PC_ADJUST)))
390 if (current->return_address < exclude_min
391 || current->return_address > exclude_max)
392 array[cnt++] = current->return_address + PC_ADJUST;
394 current = (struct layout *) ((size_t) current->next + FRAME_OFFSET);
401 /* No target specific implementation and PC_ADJUST not defined. */
403 /*------------------------------*
404 *-- The dummy implementation --*
405 *------------------------------*/
408 __gnat_backtrace (array, size, exclude_min, exclude_max, skip_frames)
409 void **array ATTRIBUTE_UNUSED;
410 int size ATTRIBUTE_UNUSED;
411 void *exclude_min ATTRIBUTE_UNUSED;
412 void *exclude_max ATTRIBUTE_UNUSED;
413 int skip_frames ATTRIBUTE_UNUSED;