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Date:	Sun, 16 Oct 2011 14:31:37 -0700 (PDT)
From:	"jan.kolar" <kolar AT math DOT cas DOT cz>
To:	cygwin AT cygwin DOT com
Subject:	Re: /proc/*/cmdline corrupted
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> 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
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