Re: Automatically use hardware watchpoints

Vladimir Prus
2006-11-08T18:55:34Z

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Vladimir Prus wrote:

>
> Hello!
>
> At the moment, gdb is not very good at debugging applications in flash:
> - you must remember to use 'hbreak' and not 'break'
> - a number of commands (like "next") want to use breakpoints
> internally. Since software breakpoints do no work, those commands
> do no work either.
>
> This patch makes insert_bp_location automatically decide what breakpoint
> type should be used if the target provides a memory map.

And here's a version of this patch that actually includes doc changes.

- Volodya

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Index: Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/Makefile.in,v
retrieving revision 1.847
diff -u -r1.847 Makefile.in
--- Makefile.in 17 Oct 2006 20:17:44 -0000 1.847
+++ Makefile.in 1 Nov 2006 11:12:53 -0000
@@ -1832,7 +1832,8 @@
$(gdb_string_h) $(demangle_h) $(annotate_h) $(symfile_h) \
$(objfiles_h) $(source_h) $(linespec_h) $(completer_h) $(gdb_h) \
$(ui_out_h) $(cli_script_h) $(gdb_assert_h) $(block_h) $(solib_h) \
- $(solist_h) $(observer_h) $(exceptions_h) $(gdb_events_h) $(mi_common_h)
+ $(solist_h) $(observer_h) $(exceptions_h) $(gdb_events_h) $(mi_common_h) \
+ $(memattr_h)
bsd-kvm.o: bsd-kvm.c $(defs_h) $(cli_cmds_h) $(command_h) $(frame_h) \
$(regcache_h) $(target_h) $(value_h) $(gdbcore_h) $(gdb_assert_h) \
$(readline_h) $(bsd_kvm_h)
Index: breakpoint.c
===================================================================
RCS file: /cvs/src/src/gdb/breakpoint.c,v
retrieving revision 1.231
diff -u -r1.231 breakpoint.c
--- breakpoint.c 19 Oct 2006 15:58:25 -0000 1.231
+++ breakpoint.c 1 Nov 2006 11:12:55 -0000
@@ -53,6 +53,7 @@
#include "solist.h"
#include "observer.h"
#include "exceptions.h"
+#include "memattr.h"

#include "gdb-events.h"
#include "mi/mi-common.h"
@@ -231,6 +232,22 @@
value);
}

+/* If 1, gdb will automatically use hardware breakpoints for breakpoints
+ set with "break" but falling in read-only memory.
+ If 0, gdb will warn about such breakpoints, but won't automatically
+ use hardware breakpoints. */
+static int automatic_hardware_breakpoints;
+static void
+show_automatic_hardware_breakpoints (struct ui_file *file, int from_tty,
+ struct cmd_list_element *c,
+ const char *value)
+{
+ fprintf_filtered (file, _("\
+Automatic usage of hardware breakpoints is %s.\n"),
+ value);
+}
+
+
void _initialize_breakpoint (void);

extern int addressprint; /* Print machine addresses? */
@@ -794,6 +811,57 @@
if (bpt->loc_type == bp_loc_software_breakpoint
|| bpt->loc_type == bp_loc_hardware_breakpoint)
{
+ if (bpt->owner->type != bp_hardware_breakpoint)
+ {
+ /* If the explicitly specified breakpoint type
+ is not hardware breakpoint, check the memory map to see
+ if the breakpoint address is in read only memory or not.
+ Two important cases are:
+ - location type is not hardware breakpoint, memory
+ is readonly. We change the type of the location to
+ hardware breakpoint.
+ - location type is hardware breakpoint, memory is read-write.
+ This means we've previously made the location hardware one, but
+ then the memory map changed, so we undo.
+
+ When breakpoints are removed, remove_breakpoints will
+ use location types we've just set here, the only possible
+ problem is that memory map has changed during running program,
+ but it's not going to work anyway with current gdb. */
+ struct mem_region *mr
+ = lookup_mem_region (bpt->target_info.placed_address);
+
+ if (mr)
+ {
+ if (automatic_hardware_breakpoints)
+ {
+ int changed = 0;
+ enum bp_loc_type new_type;
+
+ if (mr->attrib.mode != MEM_RW)
+ new_type = bp_loc_hardware_breakpoint;
+ else
+ new_type = bp_loc_software_breakpoint;
+
+ if (new_type != bpt->loc_type)
+ {
+ static int said = 0;
+ bpt->loc_type = new_type;
+ if (!said)
+ {
+ fprintf_filtered (gdb_stdout,
+ _("Note: automatically using hardware breakpoints for read-only addresses."));
+ said = 1;
+ }
+ }
+ }
+ else if (bpt->loc_type == bp_loc_software_breakpoint
+ && mr->attrib.mode != MEM_RW)
+ warning (_("cannot set software breakpoint at readonly address %s"),
+ paddr (bpt->address));
+ }
+ }
+
/* First check to see if we have to handle an overlay. */
if (overlay_debugging == ovly_off
|| bpt->section == NULL
@@ -1235,6 +1303,9 @@
if (b->inserted)
{
remove_breakpoint (b, mark_inserted);
+ /* Note: since we insert a breakpoint right after removing,
+ any decisions about automatically using hardware breakpoints
+ made in insert_bp_location are preserved. */
if (b->loc_type == bp_loc_hardware_breakpoint)
val = target_insert_hw_breakpoint (&b->target_info);
else
@@ -8127,4 +8198,18 @@
&breakpoint_show_cmdlist);

pending_break_support = AUTO_BOOLEAN_AUTO;
+
+ add_setshow_boolean_cmd ("auto-hw", no_class,
+ &automatic_hardware_breakpoints, _("\
+Set automatic usage of hardware breakpoints."), _("\
+Show automatic usage of hardware breakpoints."), _("\
+If set, the debugger will automatically use hardware breakpoints for\n\
+breakpoints set with \"break\" but falling in read-only memory. If not set,\n\
+a warning will be emitted for such breakpoints."),
+ NULL,
+ show_automatic_hardware_breakpoints,
+ &breakpoint_set_cmdlist,
+ &breakpoint_show_cmdlist);
+
+ automatic_hardware_breakpoints = 1;
}
Index: doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.366
diff -u -r1.366 gdb.texinfo
--- doc/gdb.texinfo 27 Oct 2006 22:23:20 -0000 1.366
+++ doc/gdb.texinfo 1 Nov 2006 11:13:05 -0000
@@ -3094,6 +3094,32 @@
occurred since the time the breakpoint was disabled and one or more
of these loads could resolve the location.

+@cindex automatic hardware breakpoints
+For some targets, @value{GDBN} can automatically decide if hardware or
+software breakpoints should be used, depending on whether the
+breakpoint address is read-only or read-write. This applies to
+breakpoints set with the ``break'' command as well as to internal
+breakpoints set by commands like ``next'' and ``finish''. For
+breakpoints set with ``hbreak'', @value{GDBN} will always use hardware
+breakpoints.
+
+This automatic behaviour can be controlled with the following commands::
+
+@kindex set breakpoint auto-hw
+@kindex show breakpoint auto-hw
+@table @code
+@item set breakpoint auto-hw on
+This is the default behavior. When @value{GDBN} sets a breakpoint, it
+will try to use the target memory map to decide if software or hardware
+breakpoint must be used.
+
+@item set breakpoint auto-hw off
+This indicates @value{GDBN} should not automatically select breakpoint
+type. If target provides a memory map, @value{GDBN} will warn when
+trying to set software breakpoint at a read-only address.
+@end table
+
+
@cindex negative breakpoint numbers
@cindex internal @value{GDBN} breakpoints
@value{GDBN} itself sometimes sets breakpoints in your program for