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[Gcl-devel] gclcvs dies at startup when run by non-root user

From: Camm Maguire
Subject: [Gcl-devel] gclcvs dies at startup when run by non-root user
Date: Wed, 07 Apr 2010 14:48:21 -0400

severity 572538 important

Greetings, and thank you for your detailed feedback.  This does appear
quite kernel/platform specific, as the default /sbin/sysctl
vm.mmap_min_addr on my system is 0, (default kernel, i386), and of
course I cannot reproduce your problem.  My guess is that this is also
the the default, (or the also working 65536, which probably means
"any") on the autobuilder which contructed your package.

The gcl binary is saved via unexec from an executing state on a
machine which successfully built the package (same as emacs).  My
guess also is that if you built from source, you would likely get a
working image dump.  gclcvs attempts to detect whether it can get more
heap room by lowering its start address at configure time.  If this
works, a linker script is constructed
(/usr/lib/gcl-2.7.0/unixport/gcl.script) with the correct
instructions, and perhaps 128Mb extra heap is available.  I think you
have found a situation in which such an "optimized" binary is not
portable across multiple kernel configurations.  

This is not new.  gcl must also work around sbrk randomization by the
kernel, which it attempts to do automatically at runtime.  It tests
segfault address recovery at first run of (si::sgc-on), and disables
the facility if broken on the running machine.  Certain arm machines
allowed certain assembly instructions that others simply ignored.
Finally, if some kernel security package prohibits execution from the
.data section, gcl will also bail.

I think that this is best addressed by a trap statement in the wrapper
script pointing to possible kernel settings needing adjustment.
Perhaps an external webpage with updated info as time goes on.  

Do you agree?

Take care,

Camm Maguire                                        address@hidden
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah

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