[Sbcl-devel] Bug & patch: load-1-foreign / get-dynamic-foreign-symbol-address

[Nikodemus S. <tsi...@cc...>]

Some time ago I reported a problem with accessing alien variables that are
visible in the runtime after foreign libraries have been loaded.

 http://www.caddr.com/macho/archives/sbcl-devel/2003-8/2504.html

I subsequently suggested a fix, using either the runtime dl-handle or
RTLD_DEFAULT to resolve all symbols. I have been given to understand that
this may not work on FreeBSD, however.

What follows is a minimal patch that both adds a test for this behaviour,
and fixes the issue by searching the dlhandles in reverse order
(the same order the system would when accessing via RTLD_DEFAULT or
global dlhandle).

Cheers,

  -- Nikodemus

Index: src/code/foreign.lisp
===================================================================
RCS file: /cvsroot/sbcl/sbcl/src/code/foreign.lisp,v
retrieving revision 1.18
diff -u -r1.18 foreign.lisp
--- src/code/foreign.lisp	29 Jul 2003 13:01:55 -0000	1.18
+++ src/code/foreign.lisp	18 Nov 2003 07:46:44 -0000
@@ -176,7 +176,7 @@
   ;; that the list isn't guaranteed to be in reverse order of loading,
   ;; at least not if a file is loaded more than once. Is this the
   ;; right thing? (In what cases does it matter?)
-  (dolist (handle *handles-from-dlopen*)
+  (dolist (handle (reverse *handles-from-dlopen*))
     ;; KLUDGE: We implicitly exclude the possibility that the variable
     ;; could actually be NULL, but the man page for dlsym(3)
     ;; recommends doing a more careful test. -- WHN 20000825
Index: tests/foreign.test.sh
===================================================================
RCS file: /cvsroot/sbcl/sbcl/tests/foreign.test.sh,v
retrieving revision 1.10
diff -u -r1.10 foreign.test.sh
--- tests/foreign.test.sh	8 May 2002 19:57:24 -0000	1.10
+++ tests/foreign.test.sh	18 Nov 2003 07:46:45 -0000
@@ -24,6 +24,8 @@

 # Test interaction with the shared object file.
 ${SBCL:-sbcl} <<EOF
+  (define-alien-variable environ (* c-string))
+  (defvar *environ* environ)
   (handler-case
       (load-foreign '("$testfilestem.so"))
     (sb-int:unsupported-operator ()
@@ -31,6 +33,10 @@
      ;; on every OS. In that case, there's nothing to test, and we
      ;; can just fall through to success.
      (sb-ext:quit :unix-status 52))) ; success convention for Lisp program
+  ;; Test that loading an object file didn't screw up our sense out
+  ;; of variables visible in runtime.
+  (assert (= (sb-sys:sap-int (alien-sap *environ*))
+             (sb-sys:sap-int (alien-sap environ))))
   (define-alien-routine summish int (x int) (y int))
   (assert (= (summish 10 20) 31))
   (sb-ext:quit :unix-status 52) ; success convention for Lisp program