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* *
* *
* T R A C E B A C K *
* *
* C Implementation File *
* *
* Copyright (C) 2000-2003 Ada Core Technologies, Inc. *
* *
* GNAT is free software; you can redistribute it and/or modify it under *
* terms of the GNU General Public License as published by the Free Soft- *
* ware Foundation; either version 2, or (at your option) any later ver- *
* sion. GNAT is distributed in the hope that it will be useful, but WITH- *
* OUT 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 distributed with GNAT; see file COPYING. If not, write *
* to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, *
* MA 02111-1307, USA. *
* *
* As a special exception, if you link this file with other files to *
* produce an executable, this file does not by itself cause the resulting *
* executable to be covered by the GNU General Public License. This except- *
* ion does not however invalidate any other reasons why the executable *
* file might be covered by the GNU Public License. *
* *
* GNAT was originally developed by the GNAT team at New York University. *
* Extensive contributions were provided by Ada Core Technologies Inc. *
* *
/* This file contains low level support for stack unwinding using GCC intrinsic
It has been tested on the following configurations:
#ifdef __alpha_vxworks
#include "vxWorks.h"
#ifdef IN_RTS
#define POSIX
#include "tconfig.h"
#include "tsystem.h"
#include "config.h"
#include "system.h"
extern int __gnat_backtrace (void **, int, void *, void *, int);
/* The point is to provide an implementation of the __gnat_bactrace function
above, called by the default implementation of the System.Traceback
We first have a series of target specific implementations, each included
from a separate C file for readability purposes.
Then comes a somewhat generic implementation based on a set of macro and
structure definitions which may be tailored on a per target basis. The
presence of a definition for one of these macros (PC_ADJUST) controls
wether or not the generic implementation is included.
Finally, there is a default dummy implementation, necessary to make the
linker happy on platforms where the feature is not supported, but where the
function is still referenced by the default System.Traceback. */
#define Lock_Task system__soft_links__lock_task
extern void (*Lock_Task) (void);
#define Unlock_Task system__soft_links__unlock_task
extern void (*Unlock_Task) (void);
*-- Target specific implementations --*
#if defined (__alpha_vxworks)
#include "tb-alvxw.c"
#elif defined (__ALPHA) && defined (__VMS__)
#include "tb-alvms.c"
/* No target specific implementation. */
*-- Target specific definitions for the generic implementation --*
/* The stack layout is specified by the target ABI. The "generic" scheme is
based on the following assumption:
The stack layout from some frame pointer is such that the information
required to compute the backtrace is available at static offsets.
For a given frame, the information we are interested in is the saved return
address (somewhere after the call instruction in the caller) and a pointer
to the caller's frame. The former is the base of the call chain information
we store in the tracebacks array. The latter allows us to loop over the
successive frames in the chain.
To initiate the process, we retrieve an initial frame pointer using the
appropriate GCC builtin (__builtin_frame_address).
This scheme is unfortunately not applicable on every target because the
stack layout is not necessarily regular (static) enough. On targets where
this scheme applies, the implementation relies on the following items:
o struct layout, describing the expected stack data layout relevant to the
information we are interested in,
o FRAME_OFFSET, the offset, from a given frame pointer, at which this
layout will be found,
o FRAME_LEVEL, controls how many frames up we get at to start with,
from the initial frame pointer we compute by way of the GCC builtin,
0 is most often the appropriate value. 1 may be necessary on targets
where return addresses are saved by a function in it's caller's frame
(e.g. PPC).
o PC_ADJUST, to account for the difference between a call point (address
of a call instruction), which is what we want in the output array, and
the associated return address, which is what we retrieve from the stack.
o STOP_FRAME, to decide wether we reached the top of the call chain, and
thus if the process shall stop.
: stack
| +----------------+
| +-------->| : |
| | | (FRAME_OFFSET) |
| | | : | (PC_ADJUST)
| | layout:| return_address ----------------+
| | | .... | |
+--------------- next_frame | |
| | .... | |
| | | |
| +----------------+ | +-----+
| | : |<- Base fp | | : |
| | (FRAME_OFFSET) | (FRAME_LEVEL) | | : |
| | : | +---> | [1]
| layout:| return_address --------------------> | [0]
| | ... | (PC_ADJUST) +-----+
+---------- next_frame | traceback[]
| ... |
| |
Since we inherently deal with return addresses, there is an implicit shift
by at least one for the initial point we are able to observe in the chain.
On some targets (e.g. sparc-solaris), the first return address we can
easily get without special code is even our caller's return address, so
there is a initial shift of two.
BASE_SKIP represents this initial shift, which is the minimal "skip_frames"
value we support. We could add special code for the skip_frames < BASE_SKIP
cases. This is not done currently because there is virtually no situation
in which this would be useful.
Finally, to account for some ABI specificities, a target may (but does
not have to) define:
o FORCE_CALL, to force a call to a dummy function at the very beginning
of the computation. See the PPC AIX target for an example where this
is useful.
o FETCH_UP_FRAME, to force an invocation of __builtin_frame_address with a
positive argument right after a possibly forced call even if FRAME_LEVEL
is 0. See the Sparc Solaris case for an example where this is useful.
/*------------------------------ PPC AIX -------------------------------*/
#if defined (_AIX)
struct layout
struct layout *next;
void *pad;
void *return_address;
#define FRAME_OFFSET 0
#define PC_ADJUST -4
/* The PPC ABI has an interesting specificity: the return address saved by a
function is located in it's caller's frame, and the save operation only
takes place if the function performs a call.
To have __gnat_backtrace retrieve it's own return address, we then
define ... */
#define FORCE_CALL
#define FRAME_LEVEL 1
#define BASE_SKIP 1
/*---------------------------- PPC VxWorks------------------------------*/
#elif defined (_ARCH_PPC) && defined (__vxworks)
struct layout
struct layout *next;
void *return_address;
#define FORCE_CALL
#define FRAME_LEVEL 1
/* See the PPC AIX case for an explanation of these values. */
#define FRAME_OFFSET 0
#define PC_ADJUST -4
#define STOP_FRAME(CURRENT, TOP_STACK) ((CURRENT)->return_address == 0)
#define BASE_SKIP 1
/*-------------------------- Sparc Solaris -----------------------------*/
#elif defined (sun) && defined (sparc)
/* These definitions are inspired from the Appendix D (Software
Considerations) of the SPARC V8 architecture manual. */
struct layout
struct layout *next;
void *return_address;
#define FRAME_LEVEL 0
#define FRAME_OFFSET (14 * (sizeof (void*)))
#define PC_ADJUST 0
((CURRENT)->return_address == 0|| (CURRENT)->next == 0 \
|| (void *) (CURRENT) < (TOP_STACK))
/* The sparc register windows need to be flushed before we may access them
from the stack. This is achieved by way of builtin_frame_address only
when the "count" argument is positive, so force at least one such call. */
#define BASE_SKIP 2
/* From the frame pointer of frame N, we are accessing the flushed register
window of frame N-1 (positive offset from fp), in which we retrieve the
saved return address. We then end up with our caller's return address. */
/*------------------------------- x86 ----------------------------------*/
#elif defined (i386)
struct layout
struct layout *next;
void *return_address;
#ifdef _WIN32
/* _image_base__ is the image starting address, no stack addresses should be
under this value */
extern unsigned int _image_base__;
#define LOWEST_ADDR ((unsigned int) (&_image_base__))
#define LOWEST_ADDR 0
#define FRAME_LEVEL 0
#define FRAME_OFFSET 0
#define PC_ADJUST -2
((unsigned int)(CURRENT)->return_address < LOWEST_ADDR \
|| (CURRENT)->return_address == 0|| (CURRENT)->next == 0 \
|| (void *) (CURRENT) < (TOP_STACK))
#define BASE_SKIP 1
/* On i386 architecture we check that at the call point we really have a call
insn. Possible call instructions are:
call addr16 E8 xx xx xx xx
call reg FF Dx
call off(reg) FF xx xx
lcall addr seg 9A xx xx xx xx xx xx
This check will not catch all cases but it will increase the backtrace
reliability on this architecture.
#define VALID_STACK_FRAME(ptr) \
(((*((ptr) - 3) & 0xff) == 0xe8) \
|| ((*((ptr) - 5) & 0xff) == 0x9a) \
|| ((*((ptr) - 1) & 0xff) == 0xff) \
|| (((*(ptr) & 0xd0ff) == 0xd0ff)))
*-- The generic implementation per se --*
#if defined (PC_ADJUST)
# define CURRENT_STACK_FRAME ({ char __csf; &__csf; })
#define VALID_STACK_FRAME(ptr) 1
#ifndef MAX
#define MAX(x,y) ((x) > (y) ? (x) : (y))
/* Define a dummy function to call if FORCE_CALL is defined. Don't
define it otherwise, as this could lead to "defined but not used"
warnings. */
#if defined (FORCE_CALL)
static void forced_callee () {}
__gnat_backtrace (void **array,
int size,
void *exclude_min,
void *exclude_max,
int skip_frames)
struct layout *current;
void *top_frame;
void *top_stack;
int cnt = 0;
/* Honor FORCE_CALL when defined. */
#if defined (FORCE_CALL)
forced_callee ();
/* Force a call to builtin_frame_address with a positive argument
if required. This is necessary e.g. on sparc to have the register
windows flushed before we attempt to access them on the stack. */
#if defined (FETCH_UP_FRAME_ADDRESS) && (FRAME_LEVEL == 0)
__builtin_frame_address (1);
top_frame = __builtin_frame_address (FRAME_LEVEL);
current = (struct layout *) ((size_t) top_frame + FRAME_OFFSET);
/* Skip the number of calls we have been requested to skip, accounting for
the BASE_SKIP parameter.
FRAME_LEVEL is meaningless for the count adjustment. It impacts where we
start retrieving data from, but how many frames "up" we start at is in
BASE_SKIP by definition. */
skip_frames = MAX (0, skip_frames - BASE_SKIP);
while (cnt < skip_frames)
current = (struct layout *) ((size_t) current->next + FRAME_OFFSET);
cnt = 0;
while (cnt < size)
if (STOP_FRAME (current, top_stack) ||
!VALID_STACK_FRAME((char *)(current->return_address + PC_ADJUST)))
if (current->return_address < exclude_min
|| current->return_address > exclude_max)
array[cnt++] = current->return_address + PC_ADJUST;
current = (struct layout *) ((size_t) current->next + FRAME_OFFSET);
return cnt;
/* No target specific implementation and PC_ADJUST not defined. */
*-- The dummy implementation --*
__gnat_backtrace (array, size, exclude_min, exclude_max, skip_frames)
void **array ATTRIBUTE_UNUSED;
void *exclude_min ATTRIBUTE_UNUSED;
void *exclude_max ATTRIBUTE_UNUSED;
int skip_frames ATTRIBUTE_UNUSED;
return 0;