Re: hbreak.exp: Test hardware breakpoints

Daniel Jacobowitz
2007-09-30T01:18:04Z

On Wed, Sep 26, 2007 at 03:03:32PM +0100, Maciej W. Rozycki wrote:
> I have applied all the changes from break.exp between 1.20 and 1.30 as
> you requested. Native run for i386-linux-gnu passes.
>
> 2007-09-26 Maciej W. Rozycki <macro@mips.com>
>
> * gdb.base/hbreak.exp: New test for "hbreak" and "thbreak".

Well, that didn't work out as well as I'd hoped.

Maciej posted a patch to test hardware breakpoints. It passes on
i386-linux, using current HEAD GDB. I wanted to see what would happen
when the test was run against gdbserver, which does not support
hardware breakpoints on i386 (yet). We encountered the long-standing
bug that nm-i386.h overrides target.h using #define; this means that
a native i386 GDB incorrectly tries to use ptrace even when connected
to a remote target.

I saw two ways to test: build a cross debugger or fix the bug. I
fixed the bug. Unfortunately that broke the test:

(gdb) hbreak main
No hardware breakpoint support in the target.
UNSUPPORTED: gdb.base/hbreak.exp: hardware breakpoints

This is "target exec", since we have not yet started the program.
While we were using #define to override GDB's defaults, this worked;
every target, even exec, claimed to support watchpoints. Now that
only "target child" supports hardware watchpoints, you can't insert
hardware breakpoints before the program is running.

This is the status quo on other targets too.

How do you all feel about leaving the hbreak-before-run problem for
another day, and adjusting the test to start the program running
before trying hbreak?

I've attached the patch I used.

--
Daniel Jacobowitz
CodeSourcery

2007-09-29 Daniel Jacobowitz <dan@codesourcery.com>

* Makefile.in (i386-nat.o): Update.
* amd64-linux-nat.c (_initialize_amd64_linux_nat): Call
i386_use_watchpoints.
* i386-linux-nat.c (_initialize_i386_linux_nat): Call
i386_use_watchpoints.
* i386-nat.c (i386_stopped_data_address): Take two arguments.
(i386_stopped_by_watchpoint): Update call.
(i386_can_use_hw_breakpoint, i386_use_watchpoints): New.
* config/i386/nm-i386.h: Conditionalize definitions on
! I386_WATCHPOINTS_IN_TARGET_VECTOR.
(i386_use_watchpoints): Declare.
(i386_stopped_data_address): Update.
(CHILD_POST_STARTUP_INFERIOR): Remove obsolete definition.
* config/i386/nm-linux.h (I386_WATCHPOINTS_IN_TARGET_VECTOR): Define.
* config/i386/nm-linux64.h (I386_WATCHPOINTS_IN_TARGET_VECTOR): Define.

Index: Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/Makefile.in,v
retrieving revision 1.939
diff -u -p -r1.939 Makefile.in
--- Makefile.in 27 Sep 2007 18:48:32 -0000 1.939
+++ Makefile.in 30 Sep 2007 01:14:52 -0000
@@ -2123,7 +2123,8 @@ i386-linux-tdep.o: i386-linux-tdep.c $(d
$(value_h) $(regcache_h) $(inferior_h) $(osabi_h) $(reggroups_h) \
$(dwarf2_frame_h) $(gdb_string_h) $(i386_tdep_h) \
$(i386_linux_tdep_h) $(glibc_tdep_h) $(solib_svr4_h) $(symtab_h)
-i386-nat.o: i386-nat.c $(defs_h) $(breakpoint_h) $(command_h) $(gdbcmd_h)
+i386-nat.o: i386-nat.c $(defs_h) $(breakpoint_h) $(command_h) $(gdbcmd_h) \
+ $(target_h)
i386nbsd-nat.o: i386nbsd-nat.c $(defs_h) $(gdbcore_h) $(regcache_h) \
$(target_h) $(i386_tdep_h) $(i386bsd_nat_h) $(nbsd_nat_h) \
$(bsd_kvm_h)
Index: amd64-linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/amd64-linux-nat.c,v
retrieving revision 1.17
diff -u -p -r1.17 amd64-linux-nat.c
--- amd64-linux-nat.c 23 Aug 2007 18:08:26 -0000 1.17
+++ amd64-linux-nat.c 30 Sep 2007 01:14:52 -0000
@@ -398,6 +398,8 @@ _initialize_amd64_linux_nat (void)
/* Fill in the generic GNU/Linux methods. */
t = linux_target ();

+ i386_use_watchpoints (t);
+
/* Override the GNU/Linux inferior startup hook. */
super_post_startup_inferior = t->to_post_startup_inferior;
t->to_post_startup_inferior = amd64_linux_child_post_startup_inferior;
Index: i386-linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-linux-nat.c,v
retrieving revision 1.82
diff -u -p -r1.82 i386-linux-nat.c
--- i386-linux-nat.c 23 Aug 2007 18:08:34 -0000 1.82
+++ i386-linux-nat.c 30 Sep 2007 01:14:52 -0000
@@ -805,6 +805,8 @@ _initialize_i386_linux_nat (void)
/* Fill in the generic GNU/Linux methods. */
t = linux_target ();

+ i386_use_watchpoints (t);
+
/* Override the default ptrace resume method. */
t->to_resume = i386_linux_resume;

Index: i386-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-nat.c,v
retrieving revision 1.16
diff -u -p -r1.16 i386-nat.c
--- i386-nat.c 23 Aug 2007 18:08:34 -0000 1.16
+++ i386-nat.c 30 Sep 2007 01:14:52 -0000
@@ -21,6 +21,7 @@
#include "breakpoint.h"
#include "command.h"
#include "gdbcmd.h"
+#include "target.h"

/* Support for hardware watchpoints and breakpoints using the i386
debug registers.
@@ -563,7 +564,7 @@ i386_region_ok_for_watchpoint (CORE_ADDR
Otherwise, return zero. */

int
-i386_stopped_data_address (CORE_ADDR *addr_p)
+i386_stopped_data_address (struct target_ops *ops, CORE_ADDR *addr_p)
{
CORE_ADDR addr = 0;
int i;
@@ -599,7 +600,7 @@ int
i386_stopped_by_watchpoint (void)
{
CORE_ADDR addr = 0;
- return i386_stopped_data_address (&addr);
+ return i386_stopped_data_address (&current_target, &addr);
}

/* Return non-zero if the inferior has some break/watchpoint that
@@ -654,6 +655,47 @@ i386_remove_hw_breakpoint (struct bp_tar
return retval;
}

+/* Returns the number of hardware watchpoints of type TYPE that we can
+ set. Value is positive if we can set CNT watchpoints, zero if
+ setting watchpoints of type TYPE is not supported, and negative if
+ CNT is more than the maximum number of watchpoints of type TYPE
+ that we can support. TYPE is one of bp_hardware_watchpoint,
+ bp_read_watchpoint, bp_write_watchpoint, or bp_hardware_breakpoint.
+ CNT is the number of such watchpoints used so far (including this
+ one). OTHERTYPE is non-zero if other types of watchpoints are
+ currently enabled.
+
+ We always return 1 here because we don't have enough information
+ about possible overlap of addresses that they want to watch. As an
+ extreme example, consider the case where all the watchpoints watch
+ the same address and the same region length: then we can handle a
+ virtually unlimited number of watchpoints, due to debug register
+ sharing implemented via reference counts in i386-nat.c. */
+
+static int
+i386_can_use_hw_breakpoint (int type, int cnt, int othertype)
+{
+ return 1;
+}
+
+void
+i386_use_watchpoints (struct target_ops *t)
+{
+ /* After a watchpoint trap, the PC points to the instruction after the
+ one that caused the trap. Therefore we don't need to step over it.
+ But we do need to reset the status register to avoid another trap. */
+ t->to_have_continuable_watchpoint = 1;
+
+ t->to_can_use_hw_breakpoint = i386_can_use_hw_breakpoint;
+ t->to_region_ok_for_hw_watchpoint = i386_region_ok_for_watchpoint;
+ t->to_stopped_by_watchpoint = i386_stopped_by_watchpoint;
+ t->to_stopped_data_address = i386_stopped_data_address;
+ t->to_insert_watchpoint = i386_insert_watchpoint;
+ t->to_remove_watchpoint = i386_remove_watchpoint;
+ t->to_insert_hw_breakpoint = i386_insert_hw_breakpoint;
+ t->to_remove_hw_breakpoint = i386_remove_hw_breakpoint;
+}
+
#endif /* I386_USE_GENERIC_WATCHPOINTS */
\f

Index: config/i386/nm-i386.h
===================================================================
RCS file: /cvs/src/src/gdb/config/i386/nm-i386.h,v
retrieving revision 1.10
diff -u -p -r1.10 nm-i386.h
--- config/i386/nm-i386.h 23 Aug 2007 18:08:48 -0000 1.10
+++ config/i386/nm-i386.h 30 Sep 2007 01:14:52 -0000
@@ -24,6 +24,11 @@
/* Targets should define this to use the generic x86 watchpoint support. */
#ifdef I386_USE_GENERIC_WATCHPOINTS

+/* Add watchpoint methods to the provided target_ops. Targets which call
+ this should also define I386_WATCHPOINTS_IN_TARGET_VECTOR. */
+struct target_ops;
+void i386_use_watchpoints (struct target_ops *);
+
/* Clear the reference counts and forget everything we knew about DRi. */
extern void i386_cleanup_dregs (void);

@@ -48,7 +53,7 @@ extern int i386_stopped_by_hwbp (void);
/* If the inferior has some break/watchpoint that triggered, set
the address associated with that break/watchpoint and return
true. Otherwise, return false. */
-extern int i386_stopped_data_address (CORE_ADDR *);
+extern int i386_stopped_data_address (struct target_ops *, CORE_ADDR *);

/* Insert a hardware-assisted breakpoint at BP_TGT->placed_address.
Return 0 on success, EBUSY on failure. */
@@ -59,6 +64,10 @@ extern int i386_insert_hw_breakpoint (st
Return 0 on success, -1 on failure. */
extern int i386_remove_hw_breakpoint (struct bp_target_info *bp_tgt);

+extern int i386_stopped_by_watchpoint (void);
+
+#ifndef I386_WATCHPOINTS_IN_TARGET_VECTOR
+
/* Returns the number of hardware watchpoints of type TYPE that we can
set. Value is positive if we can set CNT watchpoints, zero if
setting watchpoints of type TYPE is not supported, and negative if
@@ -90,11 +99,10 @@ extern int i386_remove_hw_breakpoint (s

#define HAVE_CONTINUABLE_WATCHPOINT 1

-extern int i386_stopped_by_watchpoint (void);
-
#define STOPPED_BY_WATCHPOINT(W) (i386_stopped_by_watchpoint () != 0)

-#define target_stopped_data_address(target, x) i386_stopped_data_address(x)
+#define target_stopped_data_address(target, x) \
+ i386_stopped_data_address(target, x)

/* Use these macros for watchpoint insertion/removal. */

@@ -110,9 +118,7 @@ extern int i386_stopped_by_watchpoint (v
#define target_remove_hw_breakpoint(bp_tgt) \
i386_remove_hw_breakpoint (bp_tgt)

-/* child_post_startup_inferior used to
- reset all debug registers by calling i386_cleanup_dregs (). */
-#define CHILD_POST_STARTUP_INFERIOR
+#endif /* I386_WATCHPOINTS_IN_TARGET_VECTOR */

#endif /* I386_USE_GENERIC_WATCHPOINTS */

Index: config/i386/nm-linux.h
===================================================================
RCS file: /cvs/src/src/gdb/config/i386/nm-linux.h,v
retrieving revision 1.26
diff -u -p -r1.26 nm-linux.h
--- config/i386/nm-linux.h 23 Aug 2007 18:08:48 -0000 1.26
+++ config/i386/nm-linux.h 30 Sep 2007 01:14:52 -0000
@@ -23,6 +23,7 @@

/* GNU/Linux supports the i386 hardware debugging registers. */
#define I386_USE_GENERIC_WATCHPOINTS
+#define I386_WATCHPOINTS_IN_TARGET_VECTOR

#include "i386/nm-i386.h"
#include "config/nm-linux.h"
Index: config/i386/nm-linux64.h
===================================================================
RCS file: /cvs/src/src/gdb/config/i386/nm-linux64.h,v
retrieving revision 1.6
diff -u -p -r1.6 nm-linux64.h
--- config/i386/nm-linux64.h 23 Aug 2007 18:08:48 -0000 1.6
+++ config/i386/nm-linux64.h 30 Sep 2007 01:14:52 -0000
@@ -24,6 +24,7 @@

/* GNU/Linux supports the i386 hardware debugging registers. */
#define I386_USE_GENERIC_WATCHPOINTS
+#define I386_WATCHPOINTS_IN_TARGET_VECTOR

#include "i386/nm-i386.h"
#include "config/nm-linux.h"