Accessing saved registers in condition handlers - VMS

This is a discussion on Accessing saved registers in condition handlers - VMS ; When a condition handler gets called due to a signal, or a trap/fault, how can the handler access the saved registers of the routine where the event happened? Some of the registers are saved in the mechanism array passed to ...

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Thread: Accessing saved registers in condition handlers

  1. Accessing saved registers in condition handlers

    When a condition handler gets called due to a signal, or a trap/fault,
    how can the handler access the saved registers of the routine where
    the event happened? Some of the registers are saved in the mechanism
    array passed to the handler, and the PC is part of the signal array,
    but some registers such as R2 aren't. The "Programming Concepts"
    manual isn't clear. All it states is "Registers R2-R15 are implicitly
    saved in the call chain". BTW, I am interested in the answer for
    Itanium. This area is rather different between VAX, Alpha and
    Itanium.

    Also, how do I access info about the routine's caller, or the caller's
    caller. This must be the call chain referred to.

  2. Re: Accessing saved registers in condition handlers

    See the calling standard manual
    http://h71000.www7.hp.com/doc/82final/5973/5973pro.html

    and the invocation context routines in the RTL
    http://h71000.www7.hp.com/doc/82fina..._invo_con_rout


  3. Re: Accessing saved registers in condition handlers

    On Oct 2, 10:47 am, IanMiller wrote:
    > See the calling standard manualhttp://h71000.www7.hp.com/doc/82final/5973/5973pro.html
    >
    > and the invocation context routines in the RTLhttp://h71000.www7.hp.com/doc/82final/5932/5932pro_023.html#get_cur_i...

    Thank you. I got what I needed.

    (they couldn't make it simple, could they?)

  4. Re: Accessing saved registers in condition handlers

    On Oct 2, 10:47 am, IanMiller wrote:
    > See the calling standard manualhttp://h71000.www7.hp.com/doc/82final/5973/5973pro.html
    >
    > and the invocation context routines in the RTLhttp://h71000.www7.hp.com/doc/82final/5932/5932pro_023.html#get_cur_i...

    OK I can call LIB$I64_GET_CURR_INVO_CONTEXT and LIB
    $I64_GET_PREV_INVO_CONTEXT and walk up the frames from a condition
    handler fine. How can I tell for sure which frame corresponds to the
    procedure that had the exception that caused the condition handler to
    be called? I match the PC from the sigargs parameter of the handler
    to the PCs in the frames and that _usually_ works. One case where it
    doesn't is if a procedure tries to call a routine at a bogus memory
    address, generating an accvio. The PC in the sigargs structure is the
    bogus address, but of course, no routine has that PC within it, so
    trying to find that PC fails. Plus I'd expect it to fail if there are
    recursive procedures, multiple frames may have the same PC.

    There seem to always be 2 frames between the faulting procedure and
    the handler. Can I assume that is _always_ the case?

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