On 05/29/2014 06:47 PM, Ondrej Oprala wrote:
> On 05/29/2014 02:45 PM, Suzuki K. Poulose wrote:
>> On 05/29/2014 05:16 PM, Ondrej Oprala wrote:
>>> On 05/29/2014 01:44 PM, Janani Venkataraman wrote:
>>>> Hi,
>>>>
>>>> We have developed a tool called "gencore" which captures the core of
>>>> an application without
>>>> disrupting its process. The dump is collected non-disruptively and
>>>> this tool currently supports
>>>> s390, x86 and power systems.
>>>>
>>>> THE TOOL:
>>>>
>>>> The tool can perform non-disruptive third party dumps. The tool also
>>>> contains a library "libgencore"
>>>> which helps applicationsto trigger self dumps.
>>>>
>>>> The tool can perform:
>>>>
>>>> 1) Third party dump: The pid of the process to dumped is given along
>>>> with name of the core-file to
>>>> be created.
>>>>
>>>> eg.
>>>>
>>>> [janani@localhost]:gencore 6616 core.test
>>>>
>>>> 2) Self dump: The programs can request a self-dump using gencore()
>>>> API, provided throughlibgencore. This
>>>> is implemented through a daemon which listens on a UNIX Filesocket for
>>>> such requests. The daemon is started
>>>> immediately post installation. The program which requires the dump
>>>> makes use of the gencore() API and provides
>>>> the name of the core-file as a parameter.
>>>>
>>>> eg.
>>>>
>>>> /* Opening the library, in this case the library is present in the
>>>> /usr/lib64 */
>>>> lib = dlopen("libgencore.so", RTLD_LAZY);
>>>>
>>>> gencore = dlsym(lib, "gencore");
>>>>
>>>> Call the API:
>>>> gencore("/home/janani/core_test").
>>>>
>>>> BASIC IDEA:
>>>>
>>>> The basic idea is that the threads of the process are held using
>>>> ptrace calls and the dump is generated in the
>>>> ELF format using the /proc/pid filesystem.
>>>>
>>>> PATCH SET:
>>>> We have designed this tool based on the discussions with linux kernel
>>>> community. The patches have been posted
>>>> at: https://lkml.org/lkml/2014/3/20/138
>>>>
>>>> Do you think this can be part of the util-linux bundle? We can tweak
>>>> it to make it work as a package in util-linux.
>>>>
>>>> Let us know your reviews and comments.
>>>>
>>>> Thanks.
>>>> Janani
>>>>
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>>> Interesting,
>>> but how is this different from attaching to a process with GDB and using
>>> the gcore command? Or to automate it more, using the gcore script that
>>> comes with GDB?
>>> Cheers,
>>> Ondrej
>>>
>> There are two major issues with that.
>>
>> 1) GDB uses PTRACE_ATTACH and hence the process gets a SIGSTOP.
> I fail to see the downside to that.
>> 2) A process cannot initiate the request to dump itself, say from a
>> signal handler. (since fork() is not signal safe)
> This should be possible using libgdb. Let's say forking while in a SIGSEGV
> handler and using the libgdb API to do the dump.
Thats exactly the problem. forking within a sighandler is not safe. You
could possibly deadlock with glibc locks.
Thanks
Suzuki
>> Thanks
>> Suzuki
>>
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> Thanks,
> Ondrej
>
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