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From (Jens-Uwe Mager)
Subject Re: DSO and core dumps for mod_perl/mod_ssl?
Date Thu, 21 Jan 1999 17:53:29 GMT

>As you can see the modules were loaded differently this time.  Especially
>mod_ssl is now at a different address and it's always at the lowest memory
>address of all DSOs. The question is _WHY_? Seems like dynamic loader
>remembers something and knows that it has to put at the first
>address and then the remaining DSOs in the middle? What's going here?

I did some truss'ing of loading of DSO's, and the dynamic linker does
not really give that load address of the DSO. It uses mmap with a zero
argument to map the code, but it uses a mmap with the MAP_FIXED
argument to mmap the data are, probably to force it to be aligned just
with the code. Thus the kernel is giving out ranges of address space
which determine the DSO load address, not the dynamic linker. Did you
look with pmap if there are mapping holes left over after unloading all
the modules right before loading them again? I would believe if parts
of the space remain mapped (forgotten munmaps?), the address space
allocator might go a different route the second time.

Jens-Uwe Mager

HELIOS Software GmbH
Steinriede 3
30827 Garbsen

Phone:		+49 5131 709320
FAX:		+49 5131 709325

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