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binutils-gdb/gdb/target-debug.h
Your Name 21c90ca166 gdb/aarch64: restore in-order watchpoint matching
At Red Hat we have an out of tree AArch64 watchpoint test which broke
after this commit:

  commit cf16ab724a
  Date:   Tue Mar 12 17:08:18 2024 +0100

      [gdb/tdep] Fix gdb.base/watch-bitfields.exp on aarch64

The problem with AArch64 hardware watchpoints is that they (as I
understand it) are restricted to a minimum of 8 bytes.  This means
that, if the thing you are watching is less than 8-bytes, then there
is always scope for invalid watchpoint triggers caused by activity in
the part of the 8-bytes that are not being watched.

Or, as is the case in this RH test, multiple watchpoint are created
within an 8-byte region, and GDB can miss-identify which watchpoint
actually triggered.

Prior to the above commit the RH test was passing.  However, the test
was relying on, in the case of ambiguity, GDB selecting the first
created watchpoint.  That behaviour changed with the above commit.
Now GDB favours reporting non write breakpoints, and will only report
a write breakpoint if no non-write breakpoint exists in the same
region.

I originally posted a patch to try and tweak the existing logic to
restore enough of the original behaviour that the RH test would pass,
this can be found here (2 iterations):

  https://inbox.sourceware.org/gdb-patches/65e746b6394f04faa027e778f733eda95d20f368.1753115072.git.aburgess@redhat.com
  https://inbox.sourceware.org/gdb-patches/638cbe9b738c0c529f6370f90ba4a395711f63ae.1753971315.git.aburgess@redhat.com

Neither of these really resolved the problem, they fixed some cases,
but broke others.

Ultimately, the problem on AArch64 is that for a single watchpoint
trap, there could be multiple watchpoints that are potentially
responsible.  The existing API defined by the target_ops methods
stopped_by_watchpoint() and stopped_data_address() only allow for two
possible options:

  1. If stopped_by_watchpoint() is true then stopped_data_address()
     can return true and a single address which identifies all
     watchpoints at that single address, or

  2. If stopped_by_watchpoint() is true then stopped_data_address()
     can return false, in which case GDB will check all write
     watchpoints to see if any have changed, if they have, then GDB
     tells the user that that was the triggering watchpoint.

If we are in a situation where we have to choose between multiple
write and read watchpoints then the current API doesn't allow the
architecture specific code to tell GDB core about this case.

In this commit I propose that we change the target_ops API,
specifically, the method:

  bool target_ops::stopped_data_address (CORE_ADDR *);

will change to:

  std::vector<CORE_ADDR> target_ops::stopped_data_addresses ();

The architecture specific code can now return a set of watchpoint
addresses, allowing GDB to identify a set of watchpoints that might
have triggered.  GDB core can then select the most likely watchpoint,
and present that to the user.

As with the old API, target_ops::stopped_data_addresses should only be
called when target_ops::stopped_by_watchpoint is true, in which case
it's return values can be interpreted like this:

  a. An empty vector; this replaces the old case where false was
     returned.  GDB should check all the write watchpoints and select
     the one that changed as the responsible watchpoint.

  b. A single entry vector; all targets except AArch64 currently
     return at most a single entry vector.  The single address
     indicates the watchpoint(s) that triggered.

  c. A multi-entry vector; currently AArch64 only.  These addresses
     indicate the set of watchpoints that might have triggered.  GDB
     will check the write watchpoints to see which (if any) changed,
     and if no write watchpoints changed, GDB will present the first
     access watchpoint.

In the future, we might want to improve the handling of (c) so that
GDB tells the user that multiple access watchpoints might have
triggered, and then list all of them.  This might clear up some
confusion.  But I think that can be done in the future (I don't have
an immediate plan to work on this).  I think this change is already a
good improvement.

The changes for this are pretty extensive, but here's a basic summary:

  * Within gdb/ changing the API name from stopped_data_address to
    stopped_data_addresses throughout.  Comments are updated too where
    needed.

  * For targets other than AArch64, the existing code is retained with
    as few changes as possible, we only allow for a single address to
    be returned, the address is now wrapped in a vector.  Where we
    used to return false, we now return the empty vector.

  * For AArch64, the return a vector logic is pushed through to
    gdb/nat/aarch64-hw-point.{c,h}, and aarch64_stopped_data_address
    changes to aarch64_stopped_data_addresses, and is updated to
    return a vector of addresses.

  * In infrun.c there's some updates to some debug output.

  * In breakpoint.c the interesting changes are in
    watchpoints_triggered.  The existing code has three cases to
    handle:

    (i) target_stopped_by_watchpoint returns false.  This case is
        unchanged.

    (ii) target_stopped_data_address returns false.  This case is now
         calling target_stopped_data_addresses, and checks for the
	 empty vector, but otherwise is unchanged.

    (iii) target_stopped_data_address returns true, and a single
          address.  This code calls target_stopped_data_addresses, and
	  now handles the possibility of a vector containing multiple
	  entries.  We need to first loop over every watchpoint
	  setting its triggered status to 'no', then we check every
	  address in the vector setting matching watchpoint's
	  triggered status to 'yes'.  But the actual logic for if a
	  watchpoint matches an address or not is unchanged.

    The important thing to notice here is that in case (iii), before
    this patch, GDB could already set _multiple_ watchpoints to
    triggered.  For example, setting a read and write watchpoint on
    the same address would result in multiple watchpoints being marked
    as triggered.  This patch just extends this so that multiple
    watchpoints, at multiple addresses, can now be marked as
    triggered.

  * In remote.c there is an interesting change.  We need to allow
    gdbserver to pass the multiple addresses back to GDB.  To achieve
    this, I now allow multiple 'watch', 'rwatch', and 'awatch' tokens
    in a 'T' stop reply packet.  This change is largely backward
    compatible.  For old versions of GDB, GDB will just use the last
    such token as the watchpoint stop address.  For new GDBs, all of
    the addresses are collected and returned from the
    target_ops::stopped_data_addresses call.  If a new GDB connects to
    an old gdbserver then it'll only get a single watchpoint address
    in the 'T' packet, but that's no worse than we are now, and will
    not cause a GDB crash, GDB will just end up checking a restricted
    set of watchpoints (which is where we are right now).

  * In gdbserver/ the changes are pretty similar.  The API is renamed
    from ::stopped_data_address to ::stopped_data_addresses, and
    ::low_stopped_data_address to ::low_stopped_data_addresses.

  * For all targets except AArch64, the existing code is retained, we
    just wrap the single address into a vector.

  * For AArch64, we call aarch64_stopped_data_addresses, which returns
    the required vector.

For testing, I've built GDB on GNU/Linux for i386, x86-64, PPC64le,
ARM, and AArch64.  That still leaves a lot of targets possibly
impacted by this change as untested.  Which is a risk.  I certainly
wouldn't want to push this patch until after GDB 17 branches so we
have time to find and fix any regressions that are introduced.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33240
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33252
2025-08-07 14:43:49 +01:00

405 lines
11 KiB
C++

/* GDB target debugging macros
Copyright (C) 2014-2025 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/>. */
#ifndef GDB_TARGET_DEBUG_H
#define GDB_TARGET_DEBUG_H
/* Printers for the debug target. Each prints an object of a given
type to a string that needn't be freed. Most printers are macros,
for brevity, but a few are static functions where more complicated
behavior is needed.
References to these printers are automatically generated by
make-target-delegates. See the generated file target-delegates-gen.c.
In a couple cases, a special printing function is defined and then
used via the TARGET_DEBUG_PRINTER macro. See target.h.
A few methods still have some explicit targetdebug code in
target.c. In most cases this is because target delegation hasn't
been done for the method; but individual cases vary. For instance,
target_store_registers does some special register printing that is
more simply done there, and target_xfer_partial additionally
bypasses the debug target. */
#include "gdbarch.h"
#include "gdbsupport/x86-xstate.h"
#include "progspace.h"
#include "target.h"
#include "target/wait.h"
#include "target/waitstatus.h"
/* The functions defined in this header file are not marked "inline", such
that any function not used by target-delegates-gen.c (the only user of this
file) will be flagged as unused. */
static std::string
target_debug_print_target_object (target_object object)
{ return plongest (object); }
static std::string
target_debug_print_CORE_ADDR (CORE_ADDR addr)
{ return core_addr_to_string (addr); }
static std::string
target_debug_print_const_char_p (const char *s)
{ return s != nullptr ? s : "(null)"; }
static std::string
target_debug_print_int (int v)
{ return plongest (v); }
static std::string
target_debug_print_bool (bool v)
{ return v ? "true" : "false"; }
static std::string
target_debug_print_long (long v)
{ return plongest (v); }
static std::string
target_debug_print_target_xfer_status (target_xfer_status status)
{ return plongest (status); }
static std::string
target_debug_print_exec_direction_kind (exec_direction_kind kind)
{ return plongest (kind); }
static std::string
target_debug_print_trace_find_type (trace_find_type type)
{ return plongest (type); }
static std::string
target_debug_print_btrace_read_type (btrace_read_type type)
{ return plongest (type); }
static std::string
target_debug_print_btrace_error (btrace_error error)
{ return plongest (error); }
static std::string
target_debug_print_ptid_t (ptid_t ptid)
{ return plongest (ptid.pid ()); }
static std::string
target_debug_print_gdbarch_p (gdbarch *arch)
{ return gdbarch_bfd_arch_info (arch)->printable_name; }
static std::string
target_debug_print_const_gdb_byte_p (const gdb_byte *p)
{ return host_address_to_string (p); }
static std::string
target_debug_print_gdb_byte_p (gdb_byte *p)
{ return host_address_to_string (p); }
static std::string
target_debug_print_const_gdb_byte_pp (const gdb_byte **p)
{ return host_address_to_string (*p); }
static std::string
target_debug_print_gdb_signal (gdb_signal sig)
{ return gdb_signal_to_name (sig); }
static std::string
target_debug_print_ULONGEST (ULONGEST v)
{ return hex_string (v); }
static std::string
target_debug_print_ULONGEST_p (ULONGEST *p)
{ return hex_string (*p); }
static std::string
target_debug_print_LONGEST (LONGEST v)
{ return phex (v, 0); }
static std::string
target_debug_print_LONGEST_p (LONGEST *p)
{ return phex (*p, 0); }
static std::string
target_debug_print_bp_target_info_p (bp_target_info *bp)
{ return core_addr_to_string (bp->placed_address); }
static std::string
target_debug_print_expression_p (expression *exp)
{ return host_address_to_string (exp); }
static std::string
target_debug_print_CORE_ADDR_p (CORE_ADDR *p)
{ return core_addr_to_string (*p); }
static std::string
target_debug_print_CORE_ADDR_r (CORE_ADDR &p)
{ return core_addr_to_string (p); }
static std::string
target_debug_print_int_p (int *p)
{ return plongest (*p); }
static std::string
target_debug_print_regcache_p (regcache *regcache)
{ return host_address_to_string (regcache); }
static std::string
target_debug_print_thread_info_p (thread_info *thread)
{ return host_address_to_string (thread); }
static std::string
target_debug_print_ui_file_p (ui_file *file)
{ return host_address_to_string (file); }
static std::string
target_debug_print_const_std_vector_target_section_p
(const std::vector<target_section> *vec)
{ return host_address_to_string (vec->data ()); }
static std::string
target_debug_print_void_p (void *p)
{ return host_address_to_string (p); }
static std::string
target_debug_print_find_memory_region_ftype (find_memory_region_ftype func)
{ return host_address_to_string (func); }
static std::string
target_debug_print_bfd_p (bfd *bfd)
{ return host_address_to_string (bfd); }
static std::string
target_debug_print_std_vector_mem_region (const std::vector<mem_region> &vec)
{ return host_address_to_string (vec.data ()); }
static std::string
target_debug_print_std_vector_CORE_ADDR (const std::vector<CORE_ADDR> &vec)
{ return host_address_to_string (vec.data ()); }
static std::string
target_debug_print_std_vector_static_tracepoint_marker
(const std::vector<static_tracepoint_marker> &vec)
{ return host_address_to_string (vec.data ()); }
static std::string
target_debug_print_const_target_desc_p (const target_desc *tdesc)
{ return host_address_to_string (tdesc); }
static std::string
target_debug_print_bp_location_p (bp_location *loc)
{ return host_address_to_string (loc); }
static std::string
target_debug_print_const_trace_state_variable_r
(const trace_state_variable &tsv)
{ return host_address_to_string (&tsv); }
static std::string
target_debug_print_trace_status_p (trace_status *status)
{ return host_address_to_string (status); }
static std::string
target_debug_print_tracepoint_p (tracepoint *tp)
{ return host_address_to_string (tp); }
static std::string
target_debug_print_uploaded_tp_p (uploaded_tp *tp)
{ return host_address_to_string (tp); }
static std::string
target_debug_print_uploaded_tp_pp (uploaded_tp **v)
{ return host_address_to_string (*v); }
static std::string
target_debug_print_uploaded_tsv_pp (uploaded_tsv **tsv)
{ return host_address_to_string (tsv); }
static std::string
target_debug_print_static_tracepoint_marker_p (static_tracepoint_marker *marker)
{ return host_address_to_string (marker); }
static std::string
target_debug_print_btrace_target_info_p (btrace_target_info *info)
{ return host_address_to_string (info); }
static std::string
target_debug_print_const_frame_unwind_p (const frame_unwind *fu)
{ return host_address_to_string (fu); }
static std::string
target_debug_print_btrace_data_p (btrace_data *data)
{ return host_address_to_string (data); }
static std::string
target_debug_print_record_method (record_method method)
{ return plongest (method); }
static std::string
target_debug_print_const_btrace_config_p (const btrace_config *config)
{ return host_address_to_string (config); }
static std::string
target_debug_print_const_btrace_target_info_p (const btrace_target_info *info)
{ return host_address_to_string (info); }
static std::string
target_debug_print_target_hw_bp_type (target_hw_bp_type type)
{ return plongest (type); }
static std::string
target_debug_print_bptype (bptype type)
{ return plongest (type); }
static std::string
target_debug_print_inferior_p (inferior *inf)
{ return host_address_to_string (inf); }
static std::string
target_debug_print_remove_bp_reason (remove_bp_reason reason)
{ return plongest (reason); }
static std::string
target_debug_print_gdb_disassembly_flags (gdb_disassembly_flags flags)
{ return plongest (flags); }
static std::string
target_debug_print_traceframe_info_up (std::unique_ptr<traceframe_info> &info)
{ return host_address_to_string (info.get ()); }
static std::string
target_debug_print_gdb_array_view_const_int
(const gdb::array_view<const int> &view)
{ return host_address_to_string (view.data ()); }
static std::string
target_debug_print_record_print_flags (record_print_flags flags)
{ return plongest (flags); }
static std::string
target_debug_print_thread_control_capabilities (thread_control_capabilities cap)
{ return plongest (cap); }
static std::string
target_debug_print_std_string (const std::string &str)
{ return str.c_str (); }
static std::string
target_debug_print_gdb_unique_xmalloc_ptr_char
(const gdb::unique_xmalloc_ptr<char> &p)
{ return p.get (); }
static std::string
target_debug_print_target_waitkind (target_waitkind kind)
{ return pulongest (kind); }
static std::string
target_debug_print_gdb_thread_options (gdb_thread_options options)
{ return to_string (options); }
static std::string
target_debug_print_target_waitstatus_p (struct target_waitstatus *status)
{ return status->to_string (); }
static std::string
target_debug_print_const_target_waitstatus_r (const target_waitstatus &status)
{ return status.to_string (); }
/* Functions that are used via TARGET_DEBUG_PRINTER. */
static std::string
target_debug_print_step (int step)
{ return step ? "step" : "continue"; }
static std::string
target_debug_print_target_wait_flags (target_wait_flags options)
{ return target_options_to_string (options); }
static std::string
target_debug_print_signals (gdb::array_view<const unsigned char> sigs)
{
std::string s = "{";
for (size_t i = 0; i < sigs.size (); i++)
if (sigs[i] != 0)
string_appendf (s, " %s",
gdb_signal_to_name (static_cast<gdb_signal>(i)));
s += " }";
return s;
}
static std::string
target_debug_print_size_t (size_t size)
{
return pulongest (size);
}
static std::string
target_debug_print_gdb_array_view_const_gdb_byte (gdb::array_view<const gdb_byte> vector)
{
std::string s = "{";
for (const auto b : vector)
string_appendf (s, " %s", phex_nz (b, 1));
s += " }";
return s;
}
static std::string
target_debug_print_const_gdb_byte_vector_r (const gdb::byte_vector &vector)
{ return target_debug_print_gdb_array_view_const_gdb_byte (vector); }
static std::string
target_debug_print_gdb_byte_vector_r (gdb::byte_vector &vector)
{ return target_debug_print_const_gdb_byte_vector_r (vector); }
static std::string
target_debug_print_x86_xsave_layout (const x86_xsave_layout &layout)
{
std::string s = string_printf ("{ sizeof_xsave=%d", layout.sizeof_xsave);
#define POFFS(region) \
if (layout.region##_offset != 0) \
string_appendf (s, ", " #region "_offset=%d", layout.region##_offset);
POFFS(avx);
POFFS(k);
POFFS(zmm_h);
POFFS(zmm);
POFFS(pkru);
#undef POFFS
s += " }";
return s;
}
static std::string
target_debug_print_displaced_step_finish_status (displaced_step_finish_status s)
{ return displaced_step_finish_status_str (s); }
static std::string
target_debug_print_displaced_step_prepare_status
(displaced_step_prepare_status s)
{ return displaced_step_prepare_status_str (s); }
#endif /* GDB_TARGET_DEBUG_H */