binutils-gdb/gdb/frame-unwind.c
Andrew Burgess 8bcb520897 gdb: Add default frame methods to gdbarch
Supply default gdbarch methods for gdbarch_dummy_id,
gdbarch_unwind_pc, and gdbarch_unwind_sp.  This patch doesn't actually
convert any targets to use these methods, and so, there will be no
user visible changes after this commit.

The implementations for default_dummy_id and default_unwind_sp are
fairly straight forward, these just take on the pattern used by most
targets.  Once these default methods are in place then most targets
will be able to switch over.

The implementation for default_unwind_pc is also fairly straight
forward, but maybe needs some explanation.

This patch has gone through a number of iterations:

  https://sourceware.org/ml/gdb-patches/2018-03/msg00165.html
  https://sourceware.org/ml/gdb-patches/2018-03/msg00306.html
  https://sourceware.org/ml/gdb-patches/2018-06/msg00090.html
  https://sourceware.org/ml/gdb-patches/2018-09/msg00127.html

and the implementation of default_unwind_pc has changed over this
time.  Originally, I took an implementation like this:

    CORE_ADDR
    default_unwind_pc (struct gdbarch *gdbarch, struct frame_info *next_frame)
    {
      int pc_regnum = gdbarch_pc_regnum (gdbarch);
      return frame_unwind_register_unsigned (next_frame, pc_regnum);
    }

This is basically a clone of default_unwind_sp, but using $pc.  It was
pointed out that we could potentially do better, and in version 2 the
implementation became:

    CORE_ADDR
    default_unwind_pc (struct gdbarch *gdbarch, struct frame_info *next_frame)
    {
      struct type *type;
      int pc_regnum;
      CORE_ADDR addr;
      struct value *value;

      pc_regnum = gdbarch_pc_regnum (gdbarch);
      value = frame_unwind_register_value (next_frame, pc_regnum);
      type = builtin_type (gdbarch)->builtin_func_ptr;
      addr = extract_typed_address (value_contents_all (value), type);
      addr = gdbarch_addr_bits_remove (gdbarch, addr);
      release_value (value);
      value_free (value);
      return addr;
    }

The idea was to try split out some of the steps of unwinding the $pc,
steps that are on some (or many) targets no-ops, and so allow targets
that do override these methods, to make use of default_unwind_pc.

This implementation remained in place for version 2, 3, and 4.

However, I realised that I'd made a mistake, most targets simply use
frame_unwind_register_unsigned to unwind the $pc, and this throws an
error if the register value is optimized out or unavailable.  My new
proposed implementation doesn't do this, I was going to end up
breaking many targets.

I considered duplicating the code from frame_unwind_register_unsigned
that throws the errors into my new default_unwind_pc, however, this
felt really overly complex.  So, what I instead went with was to
simply revert back to using frame_unwind_register_unsigned.  Almost
all existing targets already use this. Some of the ones that don't can
be converted to, which means almost all targets could end up using the
default.

One addition I have made over the version 1 implementation is to add a
call to gdbarch_addr_bits_remove.  For most targets this is a no-op,
but for a handful, having this call in place will mean that they can
use the default method.  After all this, the new default_unwind_pc now
looks like this:

    CORE_ADDR
    default_unwind_pc (struct gdbarch *gdbarch, struct frame_info *next_frame)
    {
      int pc_regnum = gdbarch_pc_regnum (gdbarch);
      CORE_ADDR pc = frame_unwind_register_unsigned (next_frame, pc_regnum);
      pc = gdbarch_addr_bits_remove (gdbarch, pc);
      return pc;
    }

gdb/ChangeLog:

	* gdb/dummy-frame.c (default_dummy_id): Defined new function.
	* gdb/dummy-frame.h (default_dummy_id): Declare new function.
	* gdb/frame-unwind.c (default_unwind_pc): Define new function.
	(default_unwind_sp): Define new function.
	* gdb/frame-unwind.h (default_unwind_pc): Declare new function.
	(default_unwind_sp): Declare new function.
	* gdb/frame.c (frame_unwind_pc): Assume gdbarch_unwind_pc is
	available.
	(get_frame_sp): Assume that gdbarch_unwind_sp is available.
	* gdb/gdbarch.c: Regenerate.
	* gdb/gdbarch.h: Regenerate.
	* gdb/gdbarch.sh: Update definition of dummy_id, unwind_pc, and
	unwind_sp.  Add additional header files to be included in
	generated file.
2018-12-19 20:59:38 +00:00

313 lines
9.4 KiB
C

/* Definitions for frame unwinder, for GDB, the GNU debugger.
Copyright (C) 2003-2018 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT 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
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
#include "frame.h"
#include "frame-unwind.h"
#include "dummy-frame.h"
#include "inline-frame.h"
#include "value.h"
#include "regcache.h"
#include "gdb_obstack.h"
#include "target.h"
static struct gdbarch_data *frame_unwind_data;
struct frame_unwind_table_entry
{
const struct frame_unwind *unwinder;
struct frame_unwind_table_entry *next;
};
struct frame_unwind_table
{
struct frame_unwind_table_entry *list;
/* The head of the OSABI part of the search list. */
struct frame_unwind_table_entry **osabi_head;
};
static void *
frame_unwind_init (struct obstack *obstack)
{
struct frame_unwind_table *table
= OBSTACK_ZALLOC (obstack, struct frame_unwind_table);
/* Start the table out with a few default sniffers. OSABI code
can't override this. */
table->list = OBSTACK_ZALLOC (obstack, struct frame_unwind_table_entry);
table->list->unwinder = &dummy_frame_unwind;
table->list->next = OBSTACK_ZALLOC (obstack,
struct frame_unwind_table_entry);
table->list->next->unwinder = &inline_frame_unwind;
/* The insertion point for OSABI sniffers. */
table->osabi_head = &table->list->next->next;
return table;
}
void
frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
const struct frame_unwind *unwinder)
{
struct frame_unwind_table *table
= (struct frame_unwind_table *) gdbarch_data (gdbarch, frame_unwind_data);
struct frame_unwind_table_entry *entry;
/* Insert the new entry at the start of the list. */
entry = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_unwind_table_entry);
entry->unwinder = unwinder;
entry->next = (*table->osabi_head);
(*table->osabi_head) = entry;
}
void
frame_unwind_append_unwinder (struct gdbarch *gdbarch,
const struct frame_unwind *unwinder)
{
struct frame_unwind_table *table
= (struct frame_unwind_table *) gdbarch_data (gdbarch, frame_unwind_data);
struct frame_unwind_table_entry **ip;
/* Find the end of the list and insert the new entry there. */
for (ip = table->osabi_head; (*ip) != NULL; ip = &(*ip)->next);
(*ip) = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_unwind_table_entry);
(*ip)->unwinder = unwinder;
}
/* Call SNIFFER from UNWINDER. If it succeeded set UNWINDER for
THIS_FRAME and return 1. Otherwise the function keeps THIS_FRAME
unchanged and returns 0. */
static int
frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
const struct frame_unwind *unwinder)
{
int res = 0;
frame_prepare_for_sniffer (this_frame, unwinder);
TRY
{
res = unwinder->sniffer (unwinder, this_frame, this_cache);
}
CATCH (ex, RETURN_MASK_ALL)
{
/* Catch all exceptions, caused by either interrupt or error.
Reset *THIS_CACHE. */
*this_cache = NULL;
frame_cleanup_after_sniffer (this_frame);
if (ex.error == NOT_AVAILABLE_ERROR)
{
/* This usually means that not even the PC is available,
thus most unwinders aren't able to determine if they're
the best fit. Keep trying. Fallback prologue unwinders
should always accept the frame. */
return 0;
}
throw_exception (ex);
}
END_CATCH
if (res)
return 1;
else
{
/* Don't set *THIS_CACHE to NULL here, because sniffer has to do
so. */
frame_cleanup_after_sniffer (this_frame);
return 0;
}
gdb_assert_not_reached ("frame_unwind_try_unwinder");
}
/* Iterate through sniffers for THIS_FRAME frame until one returns with an
unwinder implementation. THIS_FRAME->UNWIND must be NULL, it will get set
by this function. Possibly initialize THIS_CACHE. */
void
frame_unwind_find_by_frame (struct frame_info *this_frame, void **this_cache)
{
struct gdbarch *gdbarch = get_frame_arch (this_frame);
struct frame_unwind_table *table
= (struct frame_unwind_table *) gdbarch_data (gdbarch, frame_unwind_data);
struct frame_unwind_table_entry *entry;
const struct frame_unwind *unwinder_from_target;
unwinder_from_target = target_get_unwinder ();
if (unwinder_from_target != NULL
&& frame_unwind_try_unwinder (this_frame, this_cache,
unwinder_from_target))
return;
unwinder_from_target = target_get_tailcall_unwinder ();
if (unwinder_from_target != NULL
&& frame_unwind_try_unwinder (this_frame, this_cache,
unwinder_from_target))
return;
for (entry = table->list; entry != NULL; entry = entry->next)
if (frame_unwind_try_unwinder (this_frame, this_cache, entry->unwinder))
return;
internal_error (__FILE__, __LINE__, _("frame_unwind_find_by_frame failed"));
}
/* A default frame sniffer which always accepts the frame. Used by
fallback prologue unwinders. */
int
default_frame_sniffer (const struct frame_unwind *self,
struct frame_info *this_frame,
void **this_prologue_cache)
{
return 1;
}
/* The default frame unwinder stop_reason callback. */
enum unwind_stop_reason
default_frame_unwind_stop_reason (struct frame_info *this_frame,
void **this_cache)
{
struct frame_id this_id = get_frame_id (this_frame);
if (frame_id_eq (this_id, outer_frame_id))
return UNWIND_OUTERMOST;
else
return UNWIND_NO_REASON;
}
/* See frame-unwind.h. */
CORE_ADDR
default_unwind_pc (struct gdbarch *gdbarch, struct frame_info *next_frame)
{
int pc_regnum = gdbarch_pc_regnum (gdbarch);
CORE_ADDR pc = frame_unwind_register_unsigned (next_frame, pc_regnum);
pc = gdbarch_addr_bits_remove (gdbarch, pc);
return pc;
}
/* See frame-unwind.h. */
CORE_ADDR
default_unwind_sp (struct gdbarch *gdbarch, struct frame_info *next_frame)
{
int sp_regnum = gdbarch_sp_regnum (gdbarch);
return frame_unwind_register_unsigned (next_frame, sp_regnum);
}
/* Helper functions for value-based register unwinding. These return
a (possibly lazy) value of the appropriate type. */
/* Return a value which indicates that FRAME did not save REGNUM. */
struct value *
frame_unwind_got_optimized (struct frame_info *frame, int regnum)
{
struct gdbarch *gdbarch = frame_unwind_arch (frame);
struct type *type = register_type (gdbarch, regnum);
struct value *val;
/* Return an lval_register value, so that we print it as
"<not saved>". */
val = allocate_value_lazy (type);
set_value_lazy (val, 0);
mark_value_bytes_optimized_out (val, 0, TYPE_LENGTH (type));
VALUE_LVAL (val) = lval_register;
VALUE_REGNUM (val) = regnum;
VALUE_NEXT_FRAME_ID (val)
= get_frame_id (get_next_frame_sentinel_okay (frame));
return val;
}
/* Return a value which indicates that FRAME copied REGNUM into
register NEW_REGNUM. */
struct value *
frame_unwind_got_register (struct frame_info *frame,
int regnum, int new_regnum)
{
return value_of_register_lazy (frame, new_regnum);
}
/* Return a value which indicates that FRAME saved REGNUM in memory at
ADDR. */
struct value *
frame_unwind_got_memory (struct frame_info *frame, int regnum, CORE_ADDR addr)
{
struct gdbarch *gdbarch = frame_unwind_arch (frame);
struct value *v = value_at_lazy (register_type (gdbarch, regnum), addr);
set_value_stack (v, 1);
return v;
}
/* Return a value which indicates that FRAME's saved version of
REGNUM has a known constant (computed) value of VAL. */
struct value *
frame_unwind_got_constant (struct frame_info *frame, int regnum,
ULONGEST val)
{
struct gdbarch *gdbarch = frame_unwind_arch (frame);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
struct value *reg_val;
reg_val = value_zero (register_type (gdbarch, regnum), not_lval);
store_unsigned_integer (value_contents_writeable (reg_val),
register_size (gdbarch, regnum), byte_order, val);
return reg_val;
}
struct value *
frame_unwind_got_bytes (struct frame_info *frame, int regnum, gdb_byte *buf)
{
struct gdbarch *gdbarch = frame_unwind_arch (frame);
struct value *reg_val;
reg_val = value_zero (register_type (gdbarch, regnum), not_lval);
memcpy (value_contents_raw (reg_val), buf, register_size (gdbarch, regnum));
return reg_val;
}
/* Return a value which indicates that FRAME's saved version of REGNUM
has a known constant (computed) value of ADDR. Convert the
CORE_ADDR to a target address if necessary. */
struct value *
frame_unwind_got_address (struct frame_info *frame, int regnum,
CORE_ADDR addr)
{
struct gdbarch *gdbarch = frame_unwind_arch (frame);
struct value *reg_val;
reg_val = value_zero (register_type (gdbarch, regnum), not_lval);
pack_long (value_contents_writeable (reg_val),
register_type (gdbarch, regnum), addr);
return reg_val;
}
void
_initialize_frame_unwind (void)
{
frame_unwind_data = gdbarch_data_register_pre_init (frame_unwind_init);
}