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    SubjectRe: [RFC PATCH 1/1] arm64: implement live patching
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    On 6/17/21 4:29 AM, nobuta.keiya@fujitsu.com wrote:
    >
    >> It's my understanding that the two pieces of work required to enable live
    >> patching on arm are in flight upstream;
    >> - Reliable stack traces as implemented by Madhavan T. Venkataraman [1]
    >> - Objtool as implemented by Julien Thierry [2]
    >>
    >> This is the remaining part required to enable live patching on arm.
    >> Based on work by Torsten Duwe [3]
    >>
    >> Allocate a task flag used to represent the patch pending state for the
    >> task. Also implement generic functions klp_arch_set_pc() &
    >> klp_get_ftrace_location().
    >>
    >> In klp_arch_set_pc() it is sufficient to set regs->pc as in
    >> ftrace_common_return() the return address is loaded from the stack.
    >>
    >> ldr x9, [sp, #S_PC]
    >> <snip>
    >> ret x9
    >>
    >> In klp_get_ftrace_location() it is necessary to advance the address by
    >> AARCH64_INSN_SIZE (4) to point to the BL in the callsite as 2 nops were
    >> placed at the start of the function, one to be patched to save the LR and
    >> another to be patched to branch to the ftrace call, and
    >> klp_get_ftrace_location() is expected to return the address of the BL. It
    >> may also be necessary to advance the address by another AARCH64_INSN_SIZE
    >> if CONFIG_ARM64_BTI_KERNEL is enabled due to the instruction placed at the
    >> branch target to satisfy BTI,
    >>
    >> Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.com>
    >>
    >> [1] https://lkml.org/lkml/2021/5/26/1212
    >> [2] https://lkml.org/lkml/2021/3/3/1135
    >> [3] https://lkml.org/lkml/2018/10/26/536
    >> ---
    >
    > AFAIU Madhavan's patch series linked in the above [1] is currently awaiting
    > review by Mark Rutland. It seems that not only this patch series but also the
    > implementation of arch_stack_walk_reliable() at the below link is required
    > to enable livepatch.
    >

    Yes. I have a patch ready for that. But I can submit that only after the previous
    series has been accepted.

    Thanks

    Madhavan

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