Re: Non disruptive application core dump infrastructure

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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.
Thanks
Suzuki

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Thanks,
Ondrej
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