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From: Matt Dillon <dillon@FreeBSD.org>
Date: Mon, 10 Jun 2002 11:52:32 -0700 (PDT)
To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: cvs commit: src/libexec/rtld-elf/i386 reloc.c
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dillon      2002/06/10 11:52:32 PDT

  Modified files:
    libexec/rtld-elf/i386 reloc.c 
  Log:
  In tracking down an installation seg fault with then openoffice port
  Martin Blapp determined that the elf dynamic loader was at fault.  In
  particular, the loader uses alloca() to allocate a symbol cache on the
  stack.  Normally this would work just fine, but if the loader is called
  from a threaded program and the object being loaded is fairly large the
  alloca() can blow away the thread stack and effect other nearby thread
  stacks as well.  My testing showed that the symbol cache can be as large
  as 250KBytes during the openoffice port build and install sequence.  Martin
  was able to work around the problem by disabling the symbol cache
  (cache = NULL;).  However, this solution is not adequate for commit because
  it can cause an enormous cpu burden for applications which do a lot of
  dynamic loading (e.g. like konqueror).
  
  The solution is to use anonymous mmap() to temporarily allocate space to
  hold the symbol cache.  In testing I found that replacing the alloca()
  with mmap() has no observable degredation in performance.
  
  It should be noted that this bug does not necessarily cause an immediate
  crash but can instead result in long term corruption and instability in
  applications that load modules from threads.  The bug is almost certainly
  responsible for some of the instabilities found in konqueror, for example,
  and possibly netscape too.
  
  Sleuthing work by: Martin Blapp <mb@imp.ch>
  X-MFC after:    Before or after the 4.6 release depending on the release engineers
  
  Revision  Changes    Path
  1.9       +20 -8     src/libexec/rtld-elf/i386/reloc.c

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