[Info-vax] Android development Was Re: OT: Larry Ellison takes retirement as CEO of Oracle

[Stephen Hoffman]

On 2014-09-23 17:11:56 +0000, JF Mezei said:


Chapter and verse: 
<http://h71000.www7.hp.com/doc/73final/5841/5841pro_078.html#user_written_sys> 

User-written system service example code: SYS$EXAMPLES:

> On 14-09-23 09:43, John Reagan wrote:
> 
>> For such things, you write user-mode system services.

That should be "user-written system services", and not "user-mode 
system services".

> OK then. When your application does a call or a branch to and address 
> that resides in  systerm service or user written system service, what 
> causes the OS to re-evaluate what privileges become authorized (and/or 
> enabled) and what causes them to once again be re-evaluated when code 
> returns to the caller ?

System services that require these checks will typically check the 
privileges and probe argument lists and related tasks during the 
initial part of the system service code.

User-written system services acquire privileges based on the implicit 
SETPRV that is granted to inner-mode code.

The image activator and the INSTALL utility and the UWSS-specific 
Privileged Library Vector (PLV) together provide a means to allow the 
system manager to authorize the execution of inner-mode code, and the 
virtual memory management mechanisms — not privileges — are the basis 
of all VMS security.

In addition to the manuals, there are various details here 
<http://h71000.www7.hp.com/wizard/swdev/ovms-shexe-cook.html>

> When C compiler compiles my code, does it know that calling SYS$QIO 
> requires the addition of special "call" (trap or whatever) instruction 
> that it doesn't add when calling a service in another shareable image ?

The C compiler has no particular concept of access mode, nor does the 
compiler generate mode-specific code, and — beyond some C calls which 
can optionally get inlined by the compiler, and beyond some knowledge 
from scanning the C RTL entry points — the C compiler does not 
particularly differentiate RTL calls or system service calls or 
application calls.

> Are system services (and user written ones) not just a different 
> flavour of a shareable image from the compiler and linker's and perhaps 
> image actiuvator's points of view ?

Some system services are implemented via UWSS images.  Most system 
services are part of the OpenVMS executive.



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