[patch 1/2] Displaced stepping across fork/vfork

Yao Qi
2011-09-11T00:46:23Z

[-- Attachment #1: Type: text/plain, Size: 901 bytes --]

Hi,
The current displaced stepping doesn't consider the case that we set a
breakpoint on syscall insn, which will cause fork/vfork, and single step
over it with displaced stepping.

In this case, syscall insn is executed in scratch pad, and GDB will
receive TARGET_WAITKIND_FORKED and TARGET_WAITKIND_VFORKED before it
cleans up displaced stepping state. The other problem, in this case, is
that the PC of child process points to the scratch pad instead of
original program location.

This patch is to address these two problems. When GDB receives
TARGET_WAITKIND_FORKED or TARGET_WAITKIND_VFORKED, it will check whether
it has been in displaced stepping. If it is, that means GDB executed a
syscall insn in scratch pad, then, we should cleanup the displaced
stepping state, such as clean up scratch pad, and set the PC of child
process to the original location.

--
Yao (é½å°§)

[-- Attachment #2: 0014-disp-step-cross-vfork.patch --]
[-- Type: text/x-patch, Size: 6895 bytes --]

gdb/
* infrun.c (displaced_step_fixup): Move some code ...
(displaced_step_restore): ... here. New function.
(handle_inferior_event): Cleanup displaced stepping state for both
child and parent when get forked or vforked event.
* regcache.c (get_thread_arch_aspace_regcache): New function.
get_thread_arch_regcache (): Call it.
---
gdb/infrun.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-------
gdb/regcache.c | 31 +++++++++++++-------
gdb/regcache.h | 3 ++
3 files changed, 95 insertions(+), 22 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 729f148..2788b08 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1377,6 +1377,23 @@ write_memory_ptid (ptid_t ptid, CORE_ADDR memaddr,
do_cleanups (ptid_cleanup);
}

+/* Restore the contents of the copy area for thread PTID. */
+
+static void
+displaced_step_restore (struct displaced_step_inferior_state *displaced,
+ ptid_t ptid)
+{
+ ULONGEST len = gdbarch_max_insn_length (displaced->step_gdbarch);
+
+ write_memory_ptid (ptid, displaced->step_copy,
+ displaced->step_saved_copy, len);
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog, "displaced: restored %s %s\n",
+ target_pid_to_str (ptid),
+ paddress (displaced->step_gdbarch,
+ displaced->step_copy));
+}
+
static void
displaced_step_fixup (ptid_t event_ptid, enum target_signal signal)
{
@@ -1395,17 +1412,7 @@ displaced_step_fixup (ptid_t event_ptid, enum target_signal signal)

old_cleanups = make_cleanup (displaced_step_clear_cleanup, displaced);

- /* Restore the contents of the copy area. */
- {
- ULONGEST len = gdbarch_max_insn_length (displaced->step_gdbarch);
-
- write_memory_ptid (displaced->step_ptid, displaced->step_copy,
- displaced->step_saved_copy, len);
- if (debug_displaced)
- fprintf_unfiltered (gdb_stdlog, "displaced: restored %s\n",
- paddress (displaced->step_gdbarch,
- displaced->step_copy));
- }
+ displaced_step_restore (displaced, displaced->step_ptid);

/* Did the instruction complete successfully? */
if (signal == TARGET_SIGNAL_TRAP)
@@ -3407,6 +3414,60 @@ handle_inferior_event (struct execution_control_state *ecs)
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: TARGET_WAITKIND_FORKED\n");

+ /* Check inferior is in displaced stepping. */
+ {
+ struct regcache *regcache = get_thread_regcache (ecs->ptid);
+ struct gdbarch *gdbarch = get_regcache_arch (regcache);
+ struct displaced_step_inferior_state *displaced
+ = get_displaced_stepping_state (ptid_get_pid (ecs->ptid));
+
+ /* If checking displaced stepping is supported, and thread
+ ecs->ptid is being in displaced stepping. */
+ if (use_displaced_stepping (gdbarch) && displaced
+ && ptid_equal (displaced->step_ptid, ecs->ptid))
+ {
+ struct inferior *parent_inf
+ = find_inferior_pid (ptid_get_pid (ecs->ptid));
+ struct regcache *child_regcache;
+ CORE_ADDR parent_pc;
+
+ /* GDB has got TARGET_WAITKIND_FORKED or TARGET_WAITKIND_VFORKED,
+ indicating that the displaced stepping of syscall instruction
+ has been done. Perform cleanup for parent process here. Note
+ that this operation also clean up child process for vfork,
+ because their pages are shared. */
+ displaced_step_fixup (ecs->ptid, TARGET_SIGNAL_TRAP);
+
+ if (ecs->ws.kind == TARGET_WAITKIND_FORKED)
+ {
+ /* Restore scratch pad for child process. */
+ displaced_step_restore (displaced, ecs->ws.value.related_pid);
+ }
+
+ /* Since vfork/fork syscall instruction is executed in scratch pad,
+ so the PC value of child is still within the range of scratchpad.
+ Set PC of child process back to original place, that is identical
+ to father's PC value. */
+
+ child_regcache
+ = get_thread_arch_aspace_regcache (ecs->ws.value.related_pid,
+ gdbarch,
+ parent_inf->aspace);
+ /* Read PC value of father process. */
+ parent_pc = regcache_read_pc (regcache);
+
+ if (debug_displaced)
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: write child pc from %s to %s\n",
+ paddress (gdbarch,
+ regcache_read_pc (child_regcache)),
+ paddress (gdbarch, parent_pc));
+
+ regcache_write_pc (child_regcache, parent_pc);
+
+ }
+ }
+
if (!ptid_equal (ecs->ptid, inferior_ptid))
{
context_switch (ecs->ptid);
diff --git a/gdb/regcache.c b/gdb/regcache.c
index 0af93e8..c64bcb8 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -450,17 +450,34 @@ struct regcache_list
static struct regcache_list *current_regcache;

struct regcache *
-get_thread_arch_regcache (ptid_t ptid, struct gdbarch *gdbarch)
+get_thread_arch_aspace_regcache (ptid_t ptid, struct gdbarch *gdbarch,
+ struct address_space *aspace)
{
struct regcache_list *list;
struct regcache *new_regcache;
- struct address_space *aspace;

for (list = current_regcache; list; list = list->next)
if (ptid_equal (list->regcache->ptid, ptid)
&& get_regcache_arch (list->regcache) == gdbarch)
return list->regcache;

+ new_regcache = regcache_xmalloc_1 (gdbarch, aspace, 0);
+ new_regcache->ptid = ptid;
+
+ list = xmalloc (sizeof (struct regcache_list));
+ list->regcache = new_regcache;
+ list->next = current_regcache;
+ current_regcache = list;
+
+ return new_regcache;
+}
+
+struct regcache *
+get_thread_arch_regcache (ptid_t ptid, struct gdbarch *gdbarch)
+{
+
+ struct address_space *aspace;
+
/* For the benefit of "maint print registers" & co when debugging an
executable, allow dumping the regcache even when there is no
thread selected (target_thread_address_space internal-errors if
@@ -471,15 +488,7 @@ get_thread_arch_regcache (ptid_t ptid, struct gdbarch *gdbarch)
? NULL
: target_thread_address_space (ptid));

- new_regcache = regcache_xmalloc_1 (gdbarch, aspace, 0);
- new_regcache->ptid = ptid;
-
- list = xmalloc (sizeof (struct regcache_list));
- list->regcache = new_regcache;
- list->next = current_regcache;
- current_regcache = list;
-
- return new_regcache;
+ return get_thread_arch_aspace_regcache (ptid, gdbarch, aspace);
}

static ptid_t current_thread_ptid;
diff --git a/gdb/regcache.h b/gdb/regcache.h
index 7f7dc10..5531f39 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -28,6 +28,9 @@ struct address_space;
extern struct regcache *get_current_regcache (void);
extern struct regcache *get_thread_regcache (ptid_t ptid);
extern struct regcache *get_thread_arch_regcache (ptid_t, struct gdbarch *);
+extern struct regcache *get_thread_arch_aspace_regcache (ptid_t,
+ struct gdbarch *,
+ struct address_space *);

void regcache_xfree (struct regcache *regcache);
struct cleanup *make_cleanup_regcache_xfree (struct regcache *regcache);
--
1.7.0.4