[PATCH 6/6] S390: Hardware breakpoint support

Andreas Arnez
2016-09-15T12:02:06Z

Add hardware breakpoint support for S390 targets.

gdb/ChangeLog:

* s390-linux-nat.c (PER_BIT, PER_EVENT_BRANCH, PER_EVENT_IFETCH)
(PER_EVENT_STORE, PER_EVENT_NULLIFICATION)
(PER_CONTROL_BRANCH_ADDRESS, PER_CONTROL_SUSPENSION)
(PER_CONTROL_ALTERATION): New macros.
(struct s390_debug_reg_state) <break_areas>: New member.
(s390_forget_process): Free break_areas as well.
(s390_linux_new_fork): Copy break_areas as well.
(s390_prepare_to_resume): Install hardware breakpoints.
(s390_can_use_hw_breakpoint): Indicate support for hardware
breakpoints.
(s390_insert_hw_breakpoint, s390_remove_hw_breakpoint): New
linux_nat target methods.
(_initialize_s390_nat): Register them.

gdb/testsuite/ChangeLog:

* lib/gdb.exp: No longer skip hardware breakpoint tests on s390.
---
gdb/s390-linux-nat.c | 131 ++++++++++++++++++++++++++++++++++++++++++----
gdb/testsuite/lib/gdb.exp | 3 +-
2 files changed, 124 insertions(+), 10 deletions(-)

diff --git a/gdb/s390-linux-nat.c b/gdb/s390-linux-nat.c
index c5d9bd3..26c56f8 100644
--- a/gdb/s390-linux-nat.c
+++ b/gdb/s390-linux-nat.c
@@ -93,6 +93,18 @@ static const struct regset s390_64_gregset =
#define S390_PSWA_OFFSET 8
#endif

+/* PER-event mask bits and PER control bits (CR9). */
+
+#define PER_BIT(n) (1UL << (63 - (n)))
+#define PER_EVENT_BRANCH PER_BIT (32)
+#define PER_EVENT_IFETCH PER_BIT (33)
+#define PER_EVENT_STORE PER_BIT (34)
+#define PER_EVENT_NULLIFICATION PER_BIT (39)
+#define PER_CONTROL_BRANCH_ADDRESS PER_BIT (40)
+#define PER_CONTROL_SUSPENSION PER_BIT (41)
+#define PER_CONTROL_ALTERATION PER_BIT (42)
+
+
/* Fill GDB's register array with the general-purpose register values
in *REGP.

@@ -450,6 +462,7 @@ DEF_VEC_O (s390_watch_area);
struct s390_debug_reg_state
{
VEC_s390_watch_area *watch_areas;
+ VEC_s390_watch_area *break_areas;
};

/* Per-process data. */
@@ -531,6 +544,7 @@ s390_forget_process (pid_t pid)
if (proc->pid == pid)
{
VEC_free (s390_watch_area, proc->state.watch_areas);
+ VEC_free (s390_watch_area, proc->state.break_areas);
*proc_link = proc->next;
xfree (proc);
return;
@@ -564,6 +578,8 @@ s390_linux_new_fork (struct lwp_info *parent, pid_t child_pid)

child_state->watch_areas = VEC_copy (s390_watch_area,
parent_state->watch_areas);
+ child_state->break_areas = VEC_copy (s390_watch_area,
+ parent_state->break_areas);
}

/* Dump PER state. */
@@ -649,10 +665,20 @@ s390_prepare_to_resume (struct lwp_info *lp)
s390_watch_area *area;
struct arch_lwp_info *lp_priv = lwp_arch_private_info (lp);
struct s390_debug_reg_state *state = s390_get_debug_reg_state (pid);
+ int step = lwp_is_stepping (lp);

- if (lp_priv == NULL || !lp_priv->per_info_changed)
+ /* Nothing to do if there was never any PER info for this thread. */
+ if (lp_priv == NULL)
return;

+ /* If PER info has changed, update it. When single-stepping, disable
+ hardware breakpoints (if any). Otherwise we're done. */
+ if (!lp_priv->per_info_changed)
+ {
+ if (!step || VEC_empty (s390_watch_area, state->break_areas))
+ return;
+ }
+
lp_priv->per_info_changed = 0;

tid = ptid_get_lwp (ptid_of_lwp (lp));
@@ -662,8 +688,11 @@ s390_prepare_to_resume (struct lwp_info *lp)
parea.len = sizeof (per_info);
parea.process_addr = (addr_t) & per_info;
parea.kernel_addr = offsetof (struct user_regs_struct, per_info);
- if (ptrace (PTRACE_PEEKUSR_AREA, tid, &parea, 0) < 0)
- perror_with_name (_("Couldn't retrieve watchpoint status"));
+
+ /* Clear PER info, but adjust the single_step field (used by older
+ kernels only). */
+ memset (&per_info, 0, sizeof (per_info));
+ per_info.single_step = (step != 0);

if (!VEC_empty (s390_watch_area, state->watch_areas))
{
@@ -675,13 +704,45 @@ s390_prepare_to_resume (struct lwp_info *lp)
watch_hi_addr = max (watch_hi_addr, area->hi_addr);
}

- per_info.control_regs.bits.em_storage_alteration = 1;
- per_info.control_regs.bits.storage_alt_space_ctl = 1;
+ /* Enable storage-alteration events. */
+ per_info.control_regs.words.cr[0] |= (PER_EVENT_STORE
+ | PER_CONTROL_ALTERATION);
}
- else
+
+ if (!VEC_empty (s390_watch_area, state->break_areas))
{
- per_info.control_regs.bits.em_storage_alteration = 0;
- per_info.control_regs.bits.storage_alt_space_ctl = 0;
+ /* Don't install hardware breakpoints while single-stepping. But
+ re-install them afterwards. */
+ if (step)
+ lp_priv->per_info_changed = 1;
+ else
+ {
+ for (ix = 0;
+ VEC_iterate (s390_watch_area, state->break_areas, ix, area);
+ ix++)
+ {
+ watch_lo_addr = min (watch_lo_addr, area->lo_addr);
+ watch_hi_addr = max (watch_hi_addr, area->hi_addr);
+ }
+
+ /* If there's just one breakpoint, enable instruction-fetching
+ nullification events for the breakpoint address (fast).
+ Otherwise stop after any instruction within the PER area and
+ after any branch into it (slow). */
+ if (watch_hi_addr == watch_lo_addr)
+ per_info.control_regs.words.cr[0] |= (PER_EVENT_NULLIFICATION
+ | PER_EVENT_IFETCH);
+ else
+ {
+ /* The PER area must include the instruction before the
+ first breakpoint address. */
+ watch_lo_addr = watch_lo_addr > 6 ? watch_lo_addr - 6 : 0;
+ per_info.control_regs.words.cr[0]
+ |= (PER_EVENT_BRANCH
+ | PER_EVENT_IFETCH
+ | PER_CONTROL_BRANCH_ADDRESS);
+ }
+ }
}
per_info.starting_addr = watch_lo_addr;
per_info.ending_addr = watch_hi_addr;
@@ -777,11 +838,61 @@ s390_remove_watchpoint (struct target_ops *self,
return -1;
}

+/* Implement the "can_use_hw_breakpoint" target_ops method. */
+
static int
s390_can_use_hw_breakpoint (struct target_ops *self,
enum bptype type, int cnt, int othertype)
{
- return type == bp_hardware_watchpoint;
+ if (type == bp_hardware_watchpoint || type == bp_hardware_breakpoint)
+ return 1;
+ return 0;
+}
+
+/* Implement the "insert_hw_breakpoint" target_ops method. */
+
+static int
+s390_insert_hw_breakpoint (struct target_ops *self,
+ struct gdbarch *gdbarch,
+ struct bp_target_info *bp_tgt)
+{
+ s390_watch_area area;
+ struct s390_debug_reg_state *state;
+
+ area.lo_addr = bp_tgt->placed_address = bp_tgt->reqstd_address;
+ area.hi_addr = area.lo_addr;
+ state = s390_get_debug_reg_state (ptid_get_pid (inferior_ptid));
+ VEC_safe_push (s390_watch_area, state->break_areas, &area);
+
+ return s390_refresh_per_info ();
+}
+
+/* Implement the "remove_hw_breakpoint" target_ops method. */
+
+static int
+s390_remove_hw_breakpoint (struct target_ops *self,
+ struct gdbarch *gdbarch,
+ struct bp_target_info *bp_tgt)
+{
+ unsigned ix;
+ struct watch_area *area;
+ struct s390_debug_reg_state *state;
+
+ state = s390_get_debug_reg_state (ptid_get_pid (inferior_ptid));
+ for (ix = 0;
+ VEC_iterate (s390_watch_area, state->break_areas, ix, area);
+ ix++)
+ {
+ if (area->lo_addr == bp_tgt->placed_address)
+ {
+ VEC_unordered_remove (s390_watch_area, state->break_areas, ix);
+ return s390_refresh_per_info ();
+ }
+ }
+
+ fprintf_unfiltered (gdb_stderr,
+ "Attempt to remove nonexistent breakpoint.\n");
+ return -1;
}

static int
@@ -904,6 +1015,8 @@ _initialize_s390_nat (void)

/* Add our watchpoint methods. */
t->to_can_use_hw_breakpoint = s390_can_use_hw_breakpoint;
+ t->to_insert_hw_breakpoint = s390_insert_hw_breakpoint;
+ t->to_remove_hw_breakpoint = s390_remove_hw_breakpoint;
t->to_region_ok_for_hw_watchpoint = s390_region_ok_for_hw_watchpoint;
t->to_have_continuable_watchpoint = 1;
t->to_stopped_by_watchpoint = s390_stopped_by_watchpoint;
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index e538812..758db46 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -2953,7 +2953,8 @@ proc skip_hw_breakpoint_tests {} {
|| [istarget "x86_64-*-*"]
|| [istarget "ia64-*-*"]
|| [istarget "arm*-*-*"]
- || [istarget "aarch64*-*-*"]} {
+ || [istarget "aarch64*-*-*"]
+ || [istarget "s390*-*-*"] } {
return 0
}

--
2.5.0