Re: [Matlab-emacs-discuss] How to debug MEX files (C code) from Emacs?

[Dennis O. <do...@pu...>]

You can use Python as a scripting language in gdb to find the PID of a currently running MATLAB process and attach to it. I remember doing this a while back. The code was something around the lines of:

<code>

# debugging MEX files in emacs on linux

import sys
pythondir = '/usr/share/gcc-6.2.1/python'
sys.path.append(pythondir)

from libstdcxx.v6 import register_libstdcxx_printers
from subprocess import check_output

try:
    register_libstdcxx_printers(None)
except Exception as e:
    pass

# find the PID of the MATLAB process
def get_pid(name):
    return list(map(int, check_output(["pidof", name]).split()))

# set a new breakpoint, deleting any breakpoints referring to the same location
def new_bp(loc):
    bps = gdb.breakpoints()
    if bps:
        for bp in bps:
            if bp.location == loc:
                gdb.execute("d " + str(bp.number))
    # set the dummy breakpoint
    return gdb.Breakpoint(loc)

# attach to the MATLAB process. if gdb attach fails, do
#    sudo sh -c "echo 0 > /proc/sys/kernel/yama/ptrace_scope"
pids = get_pid("MATLAB")
gdb.execute("attach {:d}".format(pids[0]))

<end code>

an alternative approach is to launch matlab from gdb:

<code>

run_matlab = True

if run_matlab:
    # spawn a new MATLAB process
    matlab_dir = "/path/to/MATLAB/R2016b/bin/glnxa64/MATLAB"
    gdb.execute("file " + matlab_dir)

    # set the MATLAB_DEBUG env
    gdb_loc = "/usr/bin/gdb"
    gdb.execute("set environment MATLAB_DEBUG = " + gdb_loc)

    # need to execute this according to
    # https://www.mathworks.com/help/matlab/matlab_external/debugging-on-linux-platforms.html
    gdb.execute("handle SIGSEGV SIGBUS nostop noprint")

    # set the breakpoint at the mexFunction
    mex_Bp = new_bp("mexFunction")

    # run matlab
    gdb.execute("run -nojvm -r debug_encoder -singleCompThread")

<end code>

Dennis

Dong Tian <ti...@me...> writes:

> Hi Eric, all,
>
> Thanks for replying.
>
> It is non-trivial to attach the matlab process to gdb.
>
> Matlab provides a command line option -Dgdb to associate the Matlab process
> for gdb debugging. Would it be easier to launch "matlab-shell" with -Dgdb
> as option? Maybe your or someone else could put lights on this approach?
>
> Thanks,
> Dong
>
> On Wed, Jul 19, 2017 at 09:01:56PM +0000, Eric Ludlam wrote:
>> Hi Dong,
>>
>> You can fire up GDB from within Emacs and "attach" to a process.   Using this to attach to a process running MATLAB inside Emacs' matlab-shell will let you debug through MATLAB code and into your C++ code.
>>
>> I haven't done this in a few years, and not with Mex (I was debugging MATLAB directly) but I'm guessing the principle is the same.
>>
>> Eric
>>
>> -----Original Message-----
>> From: Dong Tian [mailto:ti...@me...]
>> Sent: Wednesday, July 19, 2017 1:56 PM
>> To: mat...@li...
>> Subject: [Matlab-emacs-discuss] How to debug MEX files (C code) from Emacs?
>>
>> Hello,
>>
>> Could anyone provide a pointer on how to debug MEX files from Emacs?
>> E.g. using gdb?
>>
>> I am familiar with the procedure of debugging pure c/c++ code or .m code from Emacs using gdb, but I don't know a good way to debug MEX file coded in C from Emacs.
>>
>> Thanks in advance,
>> Dong
>>
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