Shmuel wrote:

<snip>
Assuming that the caller has initialized the save area and subsequently 
used it in accordance with IBM linkage conventions, offset 4-7 will 
contain 4 EBCDIC characters ending iin SA only if it is 144 bytes long; 
</snip>
Not true. An example is the longest-existing. That's where the creator of 
the save area (the target module) identifies that it saved the caller's 
regs on the linkage stack so placed 'F1SA' at +4. 

<snip>
If the linkage conventions are followed, under what circumstances would 
you be unable to follow the forward chain with a little bit of work?
</snip>
Within your application, maybe, as long as it doesn't use F1SA. If it uses 
F1SA there is no way of knowing if the forward chain is 4 bytes at +8 or 8 
bytes at +136.. Once you get into the system, linkage conventions are not 
necessarily followed (and additional ones are used), for performance and 
integrity reasons. 

Peter Relson
z/OS Core Technology Design

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