• Jeffrey Lee's avatar
    Improve error handling in OS_Exit · 2054b8fe
    Jeffrey Lee authored
    The poor documentation of OS_Exit in the PRMs means there could be many
    pieces of software which are using it in a dangerous way. E.g. the
    famous issue of "OS_Exit generates a garbage error if the return code is
    out of range" that's documented in the OS StrongHelp manuals - where
    people (quite rightly) assumed that the OS would generate the "return
    code out of range" error, when in reality the OS has only ever used the
    error pointer that was supplied by the caller.
    
    Try and improve on things slightly by having OS_Exit sanity check the
    supplied error pointer before it tries to use it. This doesn't alter the
    cases where OS_Exit decides to silently ignore the supplied error
    pointer / return code (if R0 isn't word aligned, or historically, if R0
    wasn't word aligned and wasn't in the low 64MB of address space), it
    just alters the logic for what error pointer gets sent to
    OS_GenerateError when it does decide to raise an error.
    
    If the error pointer looks bad (it's below &4000 or not pointing to at
    least 8 bytes of readable memory) then it will get swapped out for one
    of the "return code out of range" errors which get used when you *Set
    Sys$ReturnCode.
    
    Version 6.70. Tagged as 'Kernel-6_70'
    2054b8fe