Allocate trampoline page, as the very first one in uprobed
task xol area, and fill it with breakpoint opcode.
Also introduce get_trampoline_vaddr() helper, to wrap the
trampoline address extraction from area->vaddr. That removes
confusion and eases the debug experience in case ->vaddr
notion will be changed.
v1 changes:
* rework get_trampoline_vaddr() helper.
* init xol_area->slot_count.
Signed-off-by: Anton Arapov <an...@redhat.com>
---
kernel/events/uprobes.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 27c964b..d3c8201 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1109,6 +1109,7 @@ static struct xol_area *get_xol_area(void)
{
struct mm_struct *mm = current->mm;
struct xol_area *area;
+ uprobe_opcode_t insn = UPROBE_SWBP_INSN;
area = mm->uprobes_state.xol_area;
if (area)
@@ -1126,7 +1127,12 @@ static struct xol_area *get_xol_area(void)
if (!area->page)
goto free_bitmap;
+ /* allocate first slot of task's xol_area for the return probes */
+ set_bit(0, area->bitmap);
+ copy_to_page(area->page, 0, &insn, UPROBE_SWBP_INSN_SIZE);
+ atomic_set(&area->slot_count, 1);
init_waitqueue_head(&area->wq);
+
if (!xol_add_vma(area))
return area;
@@ -1323,6 +1329,25 @@ static struct uprobe_task *get_utask(void)
return current->utask;
}
+/*
+ * Current area->vaddr notion assume the trampoline address is always
+ * equal area->vaddr.
+ *
+ * Returns -1 in case the xol_area is not allocated.
+ */
+static unsigned long get_trampoline_vaddr(void)
+{
+ struct xol_area *area;
+ unsigned long trampoline_vaddr = -1;
+
+ area = current->mm->uprobes_state.xol_area;
+ smp_read_barrier_depends();
+ if (area)
+ trampoline_vaddr = area->vaddr;
+
+ return trampoline_vaddr;
+}
+
/* Prepare to single-step probed instruction out of line. */
static int
pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
--
1.8.1.4
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