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Date:	Sun, 16 Oct 2011 20:16:46 -0400
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Subject:	Re: /proc/*/cmdline corrupted
From:	Jon Clugston <jon DOT clugston AT gmail DOT com>
To:	cygwin AT cygwin DOT com
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I've checked and on Linux (at least) xterm's command line is not
corrupted.  From looking at the xterm code, it would appear that the X
libraries would have to be what is corrupting the command line.  I
didn't look into the X library (XmParseCommand).


Jon

On Sun, Oct 16, 2011 at 5:31 PM, jan.kolar <kolar AT math DOT cas DOT cz> wrote:
>
>> jc807j    2668     1  0 08:59 tty0     00:00:00 xterm -e ssh server
> 80x72+285+0 -e ssh server
>> jc807j    3004     1  0 08:59 tty0     00:00:00 xterm -e ssh server
>> 80x72-8+0 -e ssh server
>> jc807j    2928  5852  0 09:12 ?        00:00:00 xterm  20000 +tb
>
>> The actual command lines for the 3 xterm processes are:
>> C:\cygwin\bin\xterm.exe -sl 20000 +tb -geometry 80x72+285+0 -e ssh server
>> C:\cygwin\bin\xterm.exe -sl 20000 +tb -geometry 80x72-8+0 -e ssh server
>> C:\cygwin\bin\xterm.exe -sl 20000 +tb
>
> xterm calls XrmParseCommand() that
> "parses an (argc, argv) pair according to the specified option table ... and
> modifies the (argc, argv) pair to remove all recognized options."
>
> Therefore
>         "-sl 20000 +tb -geometry 80x72+285+0"
> is properly removed
> and "-e ssh server" is moved to __argv[1 .. 3].
> Then __argv[4] (respectively __argv[1] for the shorter command) is assigned
> null pointer
> which results in the second "\0" in the od-output below.
>
>
> HOWEVER:
>
> Either XrmParseCommand() does not update argc
> or the change does not propagate (how would that be possible?) to __argc.
> Therefore the command lines appear corrupted this particular way.
>
>
> /proc/*/cmdline  uses a copy of __argc named __argc_safe
> which is hardly to be updated anyway.
> "   for (int i = 0; i < __argc_safe; i++) "
>
> Funny enough, /proc/self/cmdline is likely to contain shortened version of
> cmdline:
> "     for (char **a = __argv; *a; a++) "
> [ pinfo.cc from cygwin 1.7.9-1 ]
>
>
>
>> I have verified that the "/proc/*/cmdline" is the source of the
>> corrupted information.  "cmdline" from PID 2928 is:
>>
>> jc807j@~>od -c /proc/2928/cmdline
>> 0000000   x   t   e   r   m  \0  \0   2   0   0   0   0  \0   +   t   b
>> 0000020  \0
>> 0000021
>
>
>
>
>
>
> ----
>  What does xterm on different platforms ?
>  While concept of modifying own cmdline (In fact, __argv[0]) is used very
>  often to signal the process state down to the user,
>  I was never thinking of modifying argc:
>     main (int argc, char **argv)
>  :-)
>
>
> JK
> --
> View this message in context: http://old.nabble.com/-proc-*-cmdline-corrupted-tp32639066p32663265.html
> Sent from the Cygwin list mailing list archive at Nabble.com.
>
>
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