On 3/30/2012 2:37 PM, Tony Harminc wrote:
On 30 March 2012 14:22, Steve Comstock<[email protected]> wrote:
On 3/30/2012 12:13 PM, Tony Harminc wrote:
[...]
Is it not generally the case that LE assembler can make itself non-LE
for purposes of calling something, just by not passing the appropriate
value in R12?
Whoa! That's news to me!!
I don't think so.
R12 points to the Common Anchor Area; being LE-conforming
means, among other things, that an ESTAE (and usually an
ESPIE) is established; a heap and a stack have been acquired,
and other infrastructure put into place.
Sure. I am not claiming that simply clearing R12 deletes the LE
environment - certainly not. But how does a called program determine
that its caller does have an LE environment set up? Is it not a
requirement that a valid R12 be passed in, and if it is not, what does
a called LE (main) program do?
Well, HLLs have built in checking: if they are a subroutine,
they expect LE to be established; if they are main, they are
responsible for setting up the environment.
So if you call an LE main program from a program that is not
LE (or is pretending to not be LE), the main program will go
ahead and establish an LE environment.
You can actually follow some control block chains to quickly
find out if an LE environment has been established.
That being said, LE Assembler can call non-LE programs (usually
Assembler themselves) with no problem (well, there are a few
sticky situations), with no need to change R12 contents.
Sure - but that's a quite different situation. We are talking about LE
assembler calling LE assembler when it may be desirable that the
called program not perceive that the caller is LE enabled.
I guess I just don't see the scenario where you want to do this.
Tony H.
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