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Date: Fri, 24 Aug 2012 09:34:29 -0600
From: John Hein <jhein@symmetricom.com>
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Cc: 
Subject: Re: LD_PRELOADed code before or after exec - different behavior
	after 6.x
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John Hein wrote at 09:17 -0600 on Aug 24, 2012:
 > 
 > head sl.cc pe.c
 > ==> sl.cc <==
 > #include <cstdio>
 > #include <cstdlib>
 > class C
 > {
 > public:
 >  C(){
 >   printf("C\n");
 >   unsetenv("XXX");
 >  }
 > };
 > static C c;
 > 
 > ==> pe.c <==
 > #include <stdio.h>
 > #include <stdlib.h>
 > int
 > main()
 > {
 >   char *p=getenv("XXX");
 >   if (p != NULL)
 >    printf("XXX=%s\n",p);
 >   return 0;
 > }
 > 
 > 
 > % g++ -fpic -shared sl.cc -o sl.so
 > % gcc pe.c -o pe
 > 
 > 7.x & 8.x ...
 > % sh -c 'XXX=1 LD_PRELOAD=$(pwd)/sl.so pe'
 > C
 > XXX=1

I meant to write:

7.x & 8.x ...
% sh -c 'XXX=1 LD_PRELOAD=$(pwd)/sl.so pe'
C
% sh -c 'XXX=1 LD_PRELOAD=$(pwd)/sl.so exec pe'
C
XXX=1

 > 6.x & 4.x ...
 > % sh -c 'XXX=1 LD_PRELOAD=$(pwd)/sl.so pe'
 > C

and
6.x & 4.x ...
% sh -c 'XXX=1 LD_PRELOAD=$(pwd)/sl.so pe'
C
% sh -c 'XXX=1 LD_PRELOAD=$(pwd)/sl.so exec pe'
C


 > In 6.x and earlier (fedora 16, too), the unsetenv clears the XXX env
 > var apparently in time to affect the exec'd process.  In 8.x & 9.x, it
 > seems the environment is set and passed to the exec'd process and the
 > LD_PRELOADed code does not affect that despite its best efforts.
 > 
 > It seems to me that 6.x behavior is more correct, but I'm seeking
 > opinions before contemplating if / how to put together a fix.
 >