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SubjectRe: Question: livepatch failed for new fork() task stack unreliable
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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;

thanks,

Wang ShaoBo

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