#401 Invalid null pointer in a saved image

lisp error
closed-invalid
ffi (23)
5
2007-03-01
2007-02-14
No

When loading an image where a variable was set to a null foreign pointer, like:
(defvar null-ptr (ffi:unsigned-foreign-address 0))

access to null-ptr returns an invalid foreign pointer, instead of valid (as it was before the image was saved and stopped). Here's a sample code that demonstrates this problem:
,-----
| (asdf:operate 'asdf:load-op 'cffi)
| (asdf:operate 'asdf:load-op 'cffi-uffi-compat)
| (defvar my-null-ptr (ffi:unsigned-foreign-address 0))
| (format t "- Before loading image, null ptr is: ~A!~%" my-null-ptr)
| (ext:saveinitmem "test.exe"
| :init-function #'(lambda ()
| (format t "- After loading image, my-null-ptr yelds: ~A.~%"
my-null-ptr)
| (ext:quit))
| :NORC t
| :script t
| :executable t
| :quiet t)
`-----

The output I get when I run this code is (after the initial load messages),
,-----
| (...)
| - Before loading image, null ptr is: #<FOREIGN-ADDRESS #x00000000>!
| C:\dev\test>test
| test
| - After loading image, my-null-ptr yelds: #<INVALID FOREIGN-ADDRESS
#x00000000>.
`-----

I believe there's no point in making such null references invalid, and it breaks several code using foreign functions.

Discussion

  • Sam Steingold

    Sam Steingold - 2007-02-14

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    This is a feature, not a bug: why should we treat NULL pointers differently from all others?

    What do you need this NULL-PTR variable for?

     
  • Sam Steingold

    Sam Steingold - 2007-02-14

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    Originator: NO

    This bug report is now marked as "pending"/"invalid".
    This means that we think that the problem you report
    is not a problem with CLISP.
    Unless you - the reporter - act within 2 weeks,
    the bug will be permanently closed.
    Sorry about the inconvenience -
    we hope your silence means that
    you agree that this is not a bug in CLISP.

     
  • Sam Steingold

    Sam Steingold - 2007-02-14
    • status: open --> pending-invalid
     
  • Edgar Gonçalves

    • status: pending-invalid --> open-invalid
     
  • Edgar Gonçalves

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    user_id=816366
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    Well, I was trying to load clqsl in clisp, and it uses such a variable to either make some comparisons or to pass as (null) arguments to foreign functions. I guess it should be cheaper than having to call a function every time we need a null pointer.

    I understand why all other pointers are invalidated, but a null pointer is, and always will be, a set of zeros, so I don't see a point in making them invalid. However, if this is clisp's policy (historic reasons or others), I understand, and I'll ask clsql dev team to adapt to this issue.

     
  • Edgar Gonçalves

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    user_id=816366
    Originator: YES

    this is the standard request for more information.
    1. what is your platform?
    ("uname -a" on a Unix system)
    compiler version? libc (on Linux)?
    2. where did you get the sources? when?
    (absolute dates are prefered over the relative ones)
    3. how did you build CLISP? (what command, options &c)
    please do a clean build (remove your build directory and
    build CLISP with "./configure --build build" or at least
    do a "make distclean" before "make")
    4. if you are using pre-built binaries, the problem is likely
    to be in the incompatibilities between the platform on which
    the binary was built and yours;
    please try compiling the sources.
    5. what is the output of (lisp-implementation-version)?
    6. what is the value of *features*?
    7. please supply the full output (copy and paste)
    of all the error messages.
    If you cannot build CLISP, you can obviously skip 5 and 6,
    but then you should provide more information in 1.
    please see <http://clisp.cons.org/clisp.html#bugs>
    for more information.
    Thanks.

    PS. This bug report is now marked "pending"
    and will auto-close unless you respond
    (in which case it will auto-re-open).

     
  • Sam Steingold

    Sam Steingold - 2007-02-14

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    Originator: NO

    > it uses such a variable to either make some comparisons

    (FFI:FOREIGN-ADDRESS-NULL foreign-entity)
    This predicate returns T if the foreign-entity refers to the NULL address (and thus foreign-entity should probably not be passed to most foreign functions).
    http://clisp.podval.org/impnotes/dffi.html#fa-null

    > to pass as (null) arguments to foreign functions.

    use NIL - it is auto-converted to NULL.

     
  • Sam Steingold

    Sam Steingold - 2007-02-14
    • assigned_to: hoehle --> sds
    • status: open-invalid --> pending-invalid
     
  • SourceForge Robot

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    user_id=1312539
    Originator: NO

    This Tracker item was closed automatically by the system. It was
    previously set to a Pending status, and the original submitter
    did not respond within 14 days (the time period specified by
    the administrator of this Tracker).

     
  • SourceForge Robot

    • status: pending-invalid --> closed-invalid
     

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