I've been doing some more investigation on this bug and have tried a
couple things to isolate it. First I ran this command:
debugger.HandleCommand("memory read --outfile /tmp/mem.txt --count
512 0x####");
It worked as expected. This leads me to believe that the bug is
somewhere in the API layer. Then I tried to disable async via
"debugger.SetAsync(false);" and the ReadMemory command started working
as expected.
So, the run lock doesn't seem to get unlocked properly when a
breakpoint is hit in the async mode. I've not had a chance to narrow
it down any further yet, but I wanted to post this up in case it rings
a bell to someone more familiar with that part of the code.
Thanks,
Mike.
On Thu, Sep 25, 2014 at 5:59 PM, Greg Clayton <gclay...@apple.com> wrote:
> When the process resumes it takes a "run lock" to stop anything else that
> requires a process to stay stopped (like memory read, register read, or
> anything involving looking at the process). Only one thing can have the run
> lock at a time. When the process stops, one or more threads can take the
> "stop lock". It is like a read/write locker where the read lock can be taken
> by N threads and they will keep anyone from acquiring the write lock, and
> only one can take the write lock (process needs to run) after all readers
> have let go of the read lock (stay stopped). So somehow this isn't working on
> the system you are debugging on. That needs to be fixed.
>
> Greg
>
>> On Sep 25, 2014, at 2:42 PM, Mikhail Sosonkin <m...@nanotick.net> wrote:
>>
>> I only have one thread in operation, so I don't expect there do be any
>> race conditions unless LLDB has its own threads under the hood. So far
>> as I can tell, this lock fails for some reason:
>>
>> Process::StopLocker stop_locker;
>> if (stop_locker.TryLock(&process_sp->GetRunLock()))
>> {
>> Mutex::Locker api_locker (process_sp->GetTarget().GetAPIMutex());
>> bytes_read = process_sp->ReadMemory (addr, dst, dst_len,
>> sb_error.ref());
>> }
>> else
>> {
>> if (log)
>> log->Printf ("SBProcess(%p)::ReadMemory() => error:
>> process is running",
>> static_cast<void*>(process_sp.get()));
>> sb_error.SetErrorString("process is running");
>> }
>>
>> At the moment, I don't know why but would be happy to hear your thoughts.
>>
>> Thanks,
>> Mike.
>>
>> On Thu, Sep 25, 2014 at 1:47 PM, Greg Clayton <gclay...@apple.com> wrote:
>>> It should be easy for you to step through the SBProcess::ReadMemory() call
>>> and see what is going wrong. If the process is stopped, it should
>>> definitely be returning memory. You are sure you don't have thread race
>>> conditions where some other thread is resuming the process?
>>>
>>>
>>>> On Sep 25, 2014, at 10:34 AM, Mikhail Sosonkin <m...@nanotick.net> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I'm trying to read some memory from a stopped process. However, the
>>>> read function errors out with "process is running" message even though
>>>> SBProcess::GetState tells me that the process is stopped. The process
>>>> was stopped because it hit a breakpoint.
>>>>
>>>> SBProcess(0x7fed13981600)::GetState () => stopped
>>>> SBProcess(0x7fed13981600)::GetState () => stopped
>>>> SBProcess(0x7fed13981600)::ReadMemory (addr=0x7fff5fc34000,
>>>> dst=0x112eff900, dst_len=4096, SBError (0x0))...
>>>> SBProcess(0x7fed13981600)::ReadMemory() => error: process is running
>>>> SBProcess(0x7fed13981600)::ReadMemory (addr=0x7fff5fc34000,
>>>> dst=0x112eff900, dst_len=4096, SBError (0x7fed12621ee0): error:
>>>> process is running) => 0
>>>>
>>>> I have two questions:
>>>> - Is this a bug/known issue? I'm using lldb library that comes with
>>>> Xcode 5 version lldb-310.2.37 (though I read somewhere that these
>>>> version numbers don't help you much).
>>>>
>>>> - Is there a mechanism to read memory of a running process?
>>>>
>>>> Thanks,
>>>> Mike.
>>>> _______________________________________________
>>>> lldb-dev mailing list
>>>> lldb-dev@cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>>>
>>
>> _______________________________________________
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>
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