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To: postgres@postgres.Berkeley.EDU
cc: Shreeniwas N Sapre <sns@asterix.cs.unipune.ernet.in>
Subject: Re: putenv in postmaster.c
In-reply-to: Shreeniwas N Sapre's message of Sat, 08 Jul 1995 16:13:07 -53000
Date: Mon, 10 Jul 95 13:09:25 -0400
From: rp2y@methi.ndim.edrc.cmu.edu
Resent-To: postgres-redist@postgres.Berkeley.EDU
Resent-Date: Mon, 10 Jul 95 10:10:44 -0700
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> The use of putenv in postmaster.c (sample below) has crashed
> postmaster on our system (DGUX 5.4R2.10). The symptom is its inability
> to find "template1" after servicing the first 2 or 3 requests. My
> diagnosis is the use of envEntry ( which is on stack) for putenv
> causing corrupted environment entries, as putenv keeps a pointer to
> the string and not a copy of the string. This problem surfaced after
> we made a few changes (unrelated to this problem) to postmaster. We
> have made envEntry as "static" as a solution.
> 
> Sample Code: 
> BackendStartup(packet, port)
> ...
> {
>     char		envEntry[4][2 * ARGV_SIZE];
>     
> ......
>     sprintf(envEntry[0], "POSTPORT=%d", PostPortName);
>     putenv(envEntry[0]);
> ...... Similar code here.
> ......
> }

First, I'm confused by the code that you posted, this obviously isn't
right since the memory allocated for envEntry is allocated on the
stack when this function is called and released when the function
returns.  I am assuming that this is the "bad" example.

Second, I'm not sure where you got this code because both Postgres V4.2
and Postgres95 actually declare envEntry as an array of pointers and
call calloc() to allocate the memory (which is probably a cleaner
solution that using a "static" array of character arrays).

BackendStartup looks like this in Postgres V4.2:

BackendStartup(packet, port)
...
{
...
    char	*envEntry[4];
    

    for (i = 0; i < 4; ++i) {
	envEntry[i] = calloc(2 * ARGV_SIZE, 1);
    }
    sprintf(envEntry[0], "POSTPORT=%d", PostPortName);
    putenv(envEntry[0]);

...
}


Robert

--
+------------------------------------------------------------------------+
| Robert Patrick (rp2y+@edrc.cmu.edu) Engineering Design Research Center |
| n-dim Group                                 Carnegie Mellon University |
| World Wide Web: http://tika.ndim.edrc.cmu.edu/~rp2y/Home.html          |
+------------------------------------------------------------------------+


--
+------------------------------------------------------------------------+
| Robert Patrick (rp2y+@edrc.cmu.edu) Engineering Design Research Center |
| n-dim Group                                 Carnegie Mellon University |
| World Wide Web: http://tika.ndim.edrc.cmu.edu/~rp2y/Home.html          |
+------------------------------------------------------------------------+


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