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Re: RFC: gdbserver crash on win XP during watchpoint removal
- From: Pedro Alves <palves at redhat dot com>
- To: Joel Brobecker <brobecker at adacore dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Wed, 15 Oct 2014 01:38:23 +0100
- Subject: Re: RFC: gdbserver crash on win XP during watchpoint removal
- Authentication-results: sourceware.org; auth=none
- References: <20141014184647 dot GB8879 at adacore dot com> <543D782F dot 10506 at redhat dot com> <20141014213727 dot GA25846 at adacore dot com>
On 10/14/2014 10:37 PM, Joel Brobecker wrote:
>> dr_control_mirror is never supposed to be updated from the target. It's a
>> one way street - the state we _want_ dr7 to have on next resume. Where is this
>> 0x400 coming from then?
>>
>> Also, what's different in native GDB? This debug registers code is
>> shared between GDB and GDBserver now.
>
> It is read back in win32-i386-low.c::i386_get_thread_context:
>
> if (th->tid == current_event->dwThreadId)
> {
> /* Copy dr values from the current thread. */
> struct x86_debug_reg_state *dr = &debug_reg_state;
> dr->dr_mirror[0] = th->context.Dr0;
> dr->dr_mirror[1] = th->context.Dr1;
> dr->dr_mirror[2] = th->context.Dr2;
> dr->dr_mirror[3] = th->context.Dr3;
> dr->dr_status_mirror = th->context.Dr6;
> dr->dr_control_mirror = th->context.Dr7;
> }
>
> debug_reg_state is a global, which is passed to x86_dr_insert_watchpoint
> in win32-i386-low.c::i386_insert_point:
>
> return x86_dr_insert_watchpoint (&debug_reg_state,
> hw_type, addr, size);
>
> i386_get_thread_context gets called after we receive the watchpoint
> signal (TARGET_WAITKIND_STOPPED) in win32_wait:
>
> case TARGET_WAITKIND_STOPPED:
> case TARGET_WAITKIND_LOADED:
> OUTMSG2 (("Child Stopped with signal = %d \n",
> ourstatus->value.sig));
>
> regcache = get_thread_regcache (current_thread, 1);
> child_fetch_inferior_registers (regcache, -1);
> return debug_event_ptid (¤t_event);
>
> It looks like just removing the statement that sets dr_control_mirror
> from the thread's DR7 is sufficient to allow hardware watchpoints
> to work again.
Yes, that sounds good enough for 7.8.1. This is OK.
> I admit I could have spent a little more time trying to understand
> the bigger picture, but I'm a bit under time pressure, so I'm hoping
> this is enough. Otherwise, I'll look at a better fix.
Hmm, I've wanted to do this for a while. So... Below's is what I
think is the better fix.
------ 8< ---------
>From 64451d0e90e363c86539236aa3b1761ca2eff0a7 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Tue, 14 Oct 2014 22:52:41 +0100
Subject: [PATCH] gdbserver/win32: Rewrite debug registers handling
Don't use debug_reg_state for both:
* "intent" - what we want the debug registers to look like
* "reality" - what/which were the contents of the DR registers when
the event triggered
Reserve it for the former only, like in the GNU/Linux port.
Otherwise the core x86 debug registers code can get confused if the
inferior itself changes the debug registers since GDB last set them.
This is also a requirement for being able to set watchpoints while the
target is running, if/when we get to it on Windows. See the big
comment in x86_dr_stopped_data_address.
Seems to me this may also fixes propagating watchpoints to all threads
-- continue_one_thread only calls win32_set_thread_context (what
copies the DR registers to the thread), if something already fetched
the thread's context before. Something else may be masking this
issue, I haven't checked.
Smoke tested by running gdbserver under Wine, connecting to it from
GNU/Linux, and checking that I could trigger a watchpoint as expected.
gdb/
2014-10-14 Pedro Alves <palves@redhat.com>
* win32-arm-low.c (arm_set_thread_context): Remove current_event
parameter.
(arm_set_thread_context): Delete.
(the_low_target): Adjust.
* win32-i386-low.c (debug_registers_changed)
(debug_registers_used): Delete.
(update_debug_registers_callback): New function.
(x86_dr_low_set_addr, x86_dr_low_set_control): Mark all threads as
needing to update their debug registers.
(win32_get_current_dr): New function.
(x86_dr_low_get_addr, x86_dr_low_get_control)
(x86_dr_low_get_status): Fetch the debug register from the thread
record's context.
(i386_initial_stuff): Adjust.
(i386_get_thread_context): Remove current_event parameter. Don't
clear debug_registers_changed nor copy DR values to
debug_reg_state.
(i386_set_thread_context): Delete.
(i386_prepare_to_resume): New function.
(i386_thread_added): Mark the thread as needing to update irs
debug registers.
(the_low_target): Remove i386_set_thread_context and install
i386_prepare_to_resume.
* win32-low.c (win32_get_thread_context): Adjust.
(win32_set_thread_context): Use SetThreadContext
directly.
(win32_prepare_to_resume): New function.
(win32_require_context): New function, factored out from ...
(thread_rec): ... this.
(continue_one_thread): Call win32_prepare_to_resume on each thread
we're about to continue.
(win32_resume): Call win32_prepare_to_resume on the event thread.
* win32-low.h (struct win32_thread_info)
<debug_registers_changed>: New field.
(struct win32_target_ops): Change prototype of set_thread_context,
delete set_thread_context and add prepare_to_resume.
(win32_require_context): New declaration.
---
gdb/gdbserver/win32-arm-low.c | 10 +--
gdb/gdbserver/win32-i386-low.c | 137 ++++++++++++++++++++++-------------------
gdb/gdbserver/win32-low.c | 73 ++++++++++++++--------
gdb/gdbserver/win32-low.h | 15 +++--
4 files changed, 134 insertions(+), 101 deletions(-)
diff --git a/gdb/gdbserver/win32-arm-low.c b/gdb/gdbserver/win32-arm-low.c
index cf64514..f4667ff 100644
--- a/gdb/gdbserver/win32-arm-low.c
+++ b/gdb/gdbserver/win32-arm-low.c
@@ -27,7 +27,7 @@ void init_registers_arm (void);
extern const struct target_desc *tdesc_arm;
static void
-arm_get_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
+arm_get_thread_context (win32_thread_info *th)
{
th->context.ContextFlags = \
CONTEXT_FULL | \
@@ -36,12 +36,6 @@ arm_get_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
GetThreadContext (th->h, &th->context);
}
-static void
-arm_set_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
-{
- SetThreadContext (th->h, &th->context);
-}
-
#define context_offset(x) ((int)&(((CONTEXT *)NULL)->x))
static const int mappings[] = {
context_offset (R0),
@@ -124,7 +118,7 @@ struct win32_target_ops the_low_target = {
sizeof (mappings) / sizeof (mappings[0]),
NULL, /* initial_stuff */
arm_get_thread_context,
- arm_set_thread_context,
+ NULL, /* prepare_to_resume */
NULL, /* thread_added */
arm_fetch_inferior_register,
arm_store_inferior_register,
diff --git a/gdb/gdbserver/win32-i386-low.c b/gdb/gdbserver/win32-i386-low.c
index b4b99e8..6d6b310 100644
--- a/gdb/gdbserver/win32-i386-low.c
+++ b/gdb/gdbserver/win32-i386-low.c
@@ -40,29 +40,36 @@ extern const struct target_desc *tdesc_i386;
static struct x86_debug_reg_state debug_reg_state;
-static int debug_registers_changed = 0;
-static int debug_registers_used = 0;
+static int
+update_debug_registers_callback (struct inferior_list_entry *entry,
+ void *pid_p)
+{
+ struct thread_info *thr = (struct thread_info *) entry;
+ win32_thread_info *th = inferior_target_data (thr);
+ int pid = *(int *) pid_p;
+
+ /* Only update the threads of this process. */
+ if (pid_of (thr) == pid)
+ {
+ /* The actual update is done later just before resuming the lwp,
+ we just mark that the registers need updating. */
+ th->debug_registers_changed = 1;
+ }
+
+ return 0;
+}
/* Update the inferior's debug register REGNUM from STATE. */
static void
x86_dr_low_set_addr (int regnum, CORE_ADDR addr)
{
- gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
-
- /* debug_reg_state.dr_mirror is already set.
- Just notify i386_set_thread_context, i386_thread_added
- that the registers need to be updated. */
- debug_registers_changed = 1;
- debug_registers_used = 1;
-}
+ /* Only update the threads of this process. */
+ int pid = pid_of (current_thread);
-static CORE_ADDR
-x86_dr_low_get_addr (int regnum)
-{
gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
- return debug_reg_state.dr_mirror[regnum];
+ find_inferior (&all_threads, update_debug_registers_callback, &pid);
}
/* Update the inferior's DR7 debug control register from STATE. */
@@ -70,17 +77,53 @@ x86_dr_low_get_addr (int regnum)
static void
x86_dr_low_set_control (unsigned long control)
{
- /* debug_reg_state.dr_control_mirror is already set.
- Just notify i386_set_thread_context, i386_thread_added
- that the registers need to be updated. */
- debug_registers_changed = 1;
- debug_registers_used = 1;
+ /* Only update the threads of this process. */
+ int pid = pid_of (current_thread);
+
+ find_inferior (&all_threads, update_debug_registers_callback, &pid);
+}
+
+/* Return the current value of a DR register of the current thread's
+ context. */
+
+static DWORD64
+win32_get_current_dr (int dr)
+{
+ win32_thread_info *th = inferior_target_data (current_thread);
+
+ win32_require_context (th);
+
+#define RET_DR(DR) \
+ case DR: \
+ return th->context.Dr ## DR
+
+ switch (dr)
+ {
+ RET_DR (0);
+ RET_DR (1);
+ RET_DR (2);
+ RET_DR (3);
+ RET_DR (6);
+ RET_DR (7);
+ }
+
+#undef RET_DR
+
+ gdb_assert_not_reached ("unhandled dr");
+}
+
+static CORE_ADDR
+x86_dr_low_get_addr (int regnum)
+{
+ gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);
+
+ return win32_get_current_dr (regnum - DR_FIRSTADDR);
}
static unsigned long
x86_dr_low_get_control (void)
{
- return debug_reg_state.dr_control_mirror;
+ return win32_get_current_dr (7);
}
/* Get the value of the DR6 debug status register from the inferior
@@ -89,9 +132,7 @@ x86_dr_low_get_control (void)
static unsigned long
x86_dr_low_get_status (void)
{
- /* We don't need to do anything here, the last call to thread_rec for
- current_event.dwThreadId id has already set it. */
- return debug_reg_state.dr_status_mirror;
+ return win32_get_current_dr (6);
}
/* Low-level function vector. */
@@ -181,12 +222,10 @@ static void
i386_initial_stuff (void)
{
x86_low_init_dregs (&debug_reg_state);
- debug_registers_changed = 0;
- debug_registers_used = 0;
}
static void
-i386_get_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
+i386_get_thread_context (win32_thread_info *th)
{
/* Requesting the CONTEXT_EXTENDED_REGISTERS register set fails if
the system doesn't support extended registers. */
@@ -210,28 +249,17 @@ i386_get_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
error ("GetThreadContext failure %ld\n", (long) e);
}
-
- debug_registers_changed = 0;
-
- if (th->tid == current_event->dwThreadId)
- {
- /* Copy dr values from the current thread. */
- struct x86_debug_reg_state *dr = &debug_reg_state;
- dr->dr_mirror[0] = th->context.Dr0;
- dr->dr_mirror[1] = th->context.Dr1;
- dr->dr_mirror[2] = th->context.Dr2;
- dr->dr_mirror[3] = th->context.Dr3;
- dr->dr_status_mirror = th->context.Dr6;
- dr->dr_control_mirror = th->context.Dr7;
- }
}
static void
-i386_set_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
+i386_prepare_to_resume (win32_thread_info *th)
{
- if (debug_registers_changed)
+ if (th->debug_registers_changed)
{
struct x86_debug_reg_state *dr = &debug_reg_state;
+
+ win32_require_context (th);
+
th->context.Dr0 = dr->dr_mirror[0];
th->context.Dr1 = dr->dr_mirror[1];
th->context.Dr2 = dr->dr_mirror[2];
@@ -239,32 +267,15 @@ i386_set_thread_context (win32_thread_info *th, DEBUG_EVENT* current_event)
/* th->context.Dr6 = dr->dr_status_mirror;
FIXME: should we set dr6 also ?? */
th->context.Dr7 = dr->dr_control_mirror;
- }
- SetThreadContext (th->h, &th->context);
+ th->debug_registers_changed = 0;
+ }
}
static void
i386_thread_added (win32_thread_info *th)
{
- /* Set the debug registers for the new thread if they are used. */
- if (debug_registers_used)
- {
- struct x86_debug_reg_state *dr = &debug_reg_state;
- th->context.ContextFlags = CONTEXT_DEBUG_REGISTERS;
- GetThreadContext (th->h, &th->context);
-
- th->context.Dr0 = dr->dr_mirror[0];
- th->context.Dr1 = dr->dr_mirror[1];
- th->context.Dr2 = dr->dr_mirror[2];
- th->context.Dr3 = dr->dr_mirror[3];
- /* th->context.Dr6 = dr->dr_status_mirror;
- FIXME: should we set dr6 also ?? */
- th->context.Dr7 = dr->dr_control_mirror;
-
- SetThreadContext (th->h, &th->context);
- th->context.ContextFlags = 0;
- }
+ th->debug_registers_changed = 1;
}
static void
@@ -450,7 +461,7 @@ struct win32_target_ops the_low_target = {
sizeof (mappings) / sizeof (mappings[0]),
i386_initial_stuff,
i386_get_thread_context,
- i386_set_thread_context,
+ i386_prepare_to_resume,
i386_thread_added,
i386_fetch_inferior_register,
i386_store_inferior_register,
diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
index ee99fe4..e714933 100644
--- a/gdb/gdbserver/win32-low.c
+++ b/gdb/gdbserver/win32-low.c
@@ -129,7 +129,7 @@ static void
win32_get_thread_context (win32_thread_info *th)
{
memset (&th->context, 0, sizeof (CONTEXT));
- (*the_low_target.get_thread_context) (th, ¤t_event);
+ (*the_low_target.get_thread_context) (th);
#ifdef _WIN32_WCE
memcpy (&th->base_context, &th->context, sizeof (CONTEXT));
#endif
@@ -153,23 +153,24 @@ win32_set_thread_context (win32_thread_info *th)
it between stopping and resuming. */
if (memcmp (&th->context, &th->base_context, sizeof (CONTEXT)) != 0)
#endif
- (*the_low_target.set_thread_context) (th, ¤t_event);
+ SetThreadContext (th->h, &th->context);
}
-/* Find a thread record given a thread id. If GET_CONTEXT is set then
- also retrieve the context for this thread. */
-static win32_thread_info *
-thread_rec (ptid_t ptid, int get_context)
+/* Set the thread context of the thread associated with TH. */
+
+static void
+win32_prepare_to_resume (win32_thread_info *th)
{
- struct thread_info *thread;
- win32_thread_info *th;
+ if (the_low_target.prepare_to_resume != NULL)
+ (*the_low_target.prepare_to_resume) (th);
+}
- thread = (struct thread_info *) find_inferior_id (&all_threads, ptid);
- if (thread == NULL)
- return NULL;
+/* See win32-low.h. */
- th = inferior_target_data (thread);
- if (get_context && th->context.ContextFlags == 0)
+void
+win32_require_context (win32_thread_info *th)
+{
+ if (th->context.ContextFlags == 0)
{
if (!th->suspended)
{
@@ -185,7 +186,23 @@ thread_rec (ptid_t ptid, int get_context)
win32_get_thread_context (th);
}
+}
+/* Find a thread record given a thread id. If GET_CONTEXT is set then
+ also retrieve the context for this thread. */
+static win32_thread_info *
+thread_rec (ptid_t ptid, int get_context)
+{
+ struct thread_info *thread;
+ win32_thread_info *th;
+
+ thread = (struct thread_info *) find_inferior_id (&all_threads, ptid);
+ if (thread == NULL)
+ return NULL;
+
+ th = inferior_target_data (thread);
+ if (get_context)
+ win32_require_context (th);
return th;
}
@@ -419,22 +436,26 @@ continue_one_thread (struct inferior_list_entry *this_thread, void *id_ptr)
int thread_id = * (int *) id_ptr;
win32_thread_info *th = inferior_target_data (thread);
- if ((thread_id == -1 || thread_id == th->tid)
- && th->suspended)
+ if (thread_id == -1 || thread_id == th->tid)
{
- if (th->context.ContextFlags)
- {
- win32_set_thread_context (th);
- th->context.ContextFlags = 0;
- }
+ win32_prepare_to_resume (th);
- if (ResumeThread (th->h) == (DWORD) -1)
+ if (th->suspended)
{
- DWORD err = GetLastError ();
- OUTMSG (("warning: ResumeThread failed in continue_one_thread, "
- "(error %d): %s\n", (int) err, strwinerror (err)));
+ if (th->context.ContextFlags)
+ {
+ win32_set_thread_context (th);
+ th->context.ContextFlags = 0;
+ }
+
+ if (ResumeThread (th->h) == (DWORD) -1)
+ {
+ DWORD err = GetLastError ();
+ OUTMSG (("warning: ResumeThread failed in continue_one_thread, "
+ "(error %d): %s\n", (int) err, strwinerror (err)));
+ }
+ th->suspended = 0;
}
- th->suspended = 0;
}
return 0;
@@ -937,6 +958,8 @@ win32_resume (struct thread_resume *resume_info, size_t n)
th = thread_rec (ptid, FALSE);
if (th)
{
+ win32_prepare_to_resume (th);
+
if (th->context.ContextFlags)
{
/* Move register values from the inferior into the thread
diff --git a/gdb/gdbserver/win32-low.h b/gdb/gdbserver/win32-low.h
index 4e84957..f4422ed 100644
--- a/gdb/gdbserver/win32-low.h
+++ b/gdb/gdbserver/win32-low.h
@@ -47,6 +47,10 @@ typedef struct win32_thread_info
/* The context of the thread, including any manipulations. */
CONTEXT context;
+
+ /* Whether debug registers change since we last set CONTEXT back to
+ the thread. */
+ int debug_registers_changed;
} win32_thread_info;
struct win32_target_ops
@@ -61,12 +65,10 @@ struct win32_target_ops
void (*initial_stuff) (void);
/* Fetch the context from the inferior. */
- void (*get_thread_context) (win32_thread_info *th,
- DEBUG_EVENT *current_event);
+ void (*get_thread_context) (win32_thread_info *th);
- /* Flush the context back to the inferior. */
- void (*set_thread_context) (win32_thread_info *th,
- DEBUG_EVENT *current_event);
+ /* Called just before resuming the thread. */
+ void (*prepare_to_resume) (win32_thread_info *th);
/* Called when a thread was added. */
void (*thread_added) (win32_thread_info *th);
@@ -96,6 +98,9 @@ struct win32_target_ops
extern struct win32_target_ops the_low_target;
+/* Retrieve the context for this thread, if not already retrieved. */
+extern void win32_require_context (win32_thread_info *th);
+
/* Map the Windows error number in ERROR to a locale-dependent error
message string and return a pointer to it. Typically, the values
for ERROR come from GetLastError.
--
1.9.3