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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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