Path: utzoo!attcan!uunet!mcvax!cernvax!ethz!pasche
From: pasche@ethz.UUCP (Stephan Pasche)
Newsgroups: comp.os.os9
Subject: Re: loading executable modules
Message-ID: <567@ethz.UUCP>
Date: 6 Aug 88 14:02:30 GMT
References: <8808031814.AA27853@jade.berkeley.edu>
Reply-To: pasche@bernina.UUCP (Stephan Paschedag)
Organization: ETH Zuerich, Switzerland
Lines: 41


Hi,
The OS-9 utility 'load' just executes the system call F$Load to get the
module to memory. F$Load has the following function :

  1. open the file
  2. check permissions
  3. allocate memory for the module
  4. load modules from file to memory
  5. add a new entry to the module directory

If the file contains more than one module, all modules are loaded into memory.
The file must belong to the user or must have public read permission, if
the file is located in the execution directory it must have execution
permission.
The module you want to load must belong to you or its module permissions
be set for legal access for you.
The memory is allocated at the highest possible physical address.
The module directory entry contains the following informations :

MD$MPtr    do.l 1  module pointer
MD$Group   do.l 1  Grp.Usr of owner
MD$Static  do.l 1  module group memory size
MD$Link    do.w 1  module link count
MD$MChk    do.w 1  module header checksum

If the header checksum in module directory and in the module do not
match, the module can not be linked/executed !
If you have a protected system, you can't write to the module directory
from user state, only from supervisor state !
The first module in the file has a link count of 1.
If the file contained more than one module, the modules can not be removed
from memory and module directory, because they are not loaded to memory
each at 16byte boundary (minimum memory allocation size).

==============================================================================
OS/2 & PS/2 : half an operating system for half a computer

Stephan Paschedag             paschedag@strati.ethz.ch or pasche@ifi.ethz.ch
Federal Institute Of Technology Zurich
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