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    SubjectRe: Question: livepatch failed for new fork() task stack unreliable
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    在 2020/6/4 10:40, Josh Poimboeuf 写道:
    > On Thu, Jun 04, 2020 at 09:24:55AM +0800, Wangshaobo (bobo) wrote:
    >> 在 2020/6/3 23:33, Josh Poimboeuf 写道:
    >>> On Wed, Jun 03, 2020 at 10:06:07PM +0800, Wangshaobo (bobo) wrote:
    >>> To be honest, I don't remember what I meant by sibling calls. They
    >>> don't even leave anything on the stack.
    >>>
    >>> For noreturns, the code might be laid out like this:
    >>>
    >>> func1:
    >>> ...
    >>> call noreturn_foo
    >>> func2:
    >>>
    >>> func2 is immediately after the call to noreturn_foo. So the return
    >>> address on the stack will actually be 'func2'. We want to retrieve the
    >>> ORC data for the call instruction (inside func1), instead of the
    >>> instruction at the beginning of func2.
    >>>
    >>> I should probably update that comment.
    >> So, I want to ask is there any side effects if i modify like this ? this
    >> modification is based on
    >>
    >> your fix. It looks like ok with proper test.
    >>
    >> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
    >> index e9cc182aa97e..ecce5051e8fd 100644
    >> --- a/arch/x86/kernel/unwind_orc.c
    >> +++ b/arch/x86/kernel/unwind_orc.c
    >> @@ -620,6 +620,7 @@ void __unwind_start(struct unwind_state *state, struct
    >> task_struct *task,
    >>                 state->sp = task->thread.sp;
    >>                 state->bp = READ_ONCE_NOCHECK(frame->bp);
    >>                 state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
    >> +              state->signal = ((void *)state->ip == ret_from_fork);
    >>         }
    >>
    >> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
    >> index 7f969b2d240f..d7396431261a 100644
    >> --- a/arch/x86/kernel/unwind_orc.c
    >> +++ b/arch/x86/kernel/unwind_orc.c
    >> @@ -540,7 +540,7 @@ bool unwind_next_frame(struct unwind_state *state)
    >>          state->sp = sp;
    >>          state->regs = NULL;
    >>          state->prev_regs = NULL;
    >> -        state->signal = ((void *)state->ip == ret_from_fork);
    >> +        state->signal = false;
    >>          break;
    > Yes that's correct.

    Hi, josh

    Could i ask when are you free to send the patch, all the tests are
    passed by.

    thanks for your help.

    Wang ShaoBo

    >

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