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Subject[RFC PATCH v4 0/6] uprobes: return probe implementation

RFC v4 uretprobes implementation. I'd be grateful for review.
/* Oleg, this one is more quirky than previous, don't beat me. */
These patches extending uprobes by enabling tools, such as perf(trace_event),
set a breakpoint on probed function's return address.

- get rid of area->rp_trampoline_vaddr as it always the same as ->vaddr
- preallocate slot, as the first one in xol_add_vma()
- cleanup ->return_uprobes list in uprobe_free_utask(), because the
task can exit from inside the ret-probe'd function(s).
- in find_active_uprobe(): Once we inserted "int3" we must ensure that
handle_swbp() will be called even if this uprobe goes away. We have
the reference but it only protects uprobe itself, it can't protect
agains delete_uprobe().
IOW, we must ensure that uprobe_pre_sstep_notifier() can't return 0.
- check, whether utask is not NULL in handle_uretprobe()
? do we want a printk() for this case?
- minor handle_uretprobe() fixups

v3 changes:
- removed uretprobe_bypass logic, it will be better to send it as
independent patch
- unified xol_get_trampoline_slot() and xol_get_insn_slot()
- protected uprobe with refcounter in prepare_uretprobe()
- uprobe_register() routine fails now, if neither consumer is set
- enclosed implementation into 1/6, 6/6 patches -ENOSYS bits

v2 changes:
- introduced rp_handler(), get rid of return_consumers
- get rid of uretprobe_[un]register()
- introduced arch_uretprobe_get_sp()
- removed uprobe_task->doomed, kill task immediately
- fix arch_uretprobe_hijack_return_addr()'s returns
- address the v1 minor issues

integrated patchset:

previous implementations:


Anton Arapov (6):
uretprobes: preparation patch
uretprobes/x86: hijack return address
uretprobes: generalize xol_get_insn_slot()
uretprobes: return probe entry, prepare uretprobe
uretprobes: invoke return probe handlers
uretprobes: implemented, thus remove -ENOSYS

arch/x86/include/asm/uprobes.h | 6 ++
arch/x86/kernel/uprobes.c | 29 +++++++++
include/linux/uprobes.h | 5 ++
kernel/events/uprobes.c | 134 ++++++++++++++++++++++++++++++++++++++---
4 files changed, 166 insertions(+), 8 deletions(-)

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