* Anton Arapov <an...@redhat.com> [2013-04-03 18:00:32]:
> 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>
Acked-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
(one small check below:)
> ---
> 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();
check: do we need this barrier?
> + 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
>
--
Thanks and Regards
Srikar Dronamraju
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