>>>>> On Tue, 11 Apr 2006 23:28:08 +0400, Samium Gromoff <[EMAIL PROTECTED]> >>>>> said: > > On Tue, 2006-04-11 at 10:30 +0100, Martin Simmons wrote: > > >>>>> On Tue, 11 Apr 2006 02:42:19 +0400, Samium Gromoff <[EMAIL > > >>>>> PROTECTED]> said: > > > Delivered-To: cffi-devel@common-lisp.net > > > > > > On Tue, 2006-04-11 at 01:55 +0400, Samium Gromoff wrote: > > > > here is the scenario: > > > > > > [snip] > > > > > > > (let ((foreign-ptr (foreign-symbol-pointer > > > > "verse_send_connect_accept" :code))) > > > > (format t "foreign-ptr contents: ") > > > > (dotimes (i 16) > > > > (format t "~2,'0X " (the (unsigned-byte 8) (mem-ref > > > > foreign-ptr :uint8 i)))) > > > > (format t "~%")) > > > > > > > > This code gives different printouts on CLISP/CMUCL/SBCL backends: > > > > > > > > CLISP: > > > > foreign-ptr contents: 55 89 E5 83 EC 28 8B 45 0C 89 44 24 04 8D 45 F8 > > > > CMUCL: > > > > foreign-ptr contents: E9 26 AE C3 F9 90 00 00 00 00 00 00 00 00 00 00 > > > > SBCL: > > > > foreign-ptr contents: E9 CE A2 A1 47 90 00 00 00 00 00 00 00 00 00 00 > > > > > > > > This amounts to foreign-symbol-pointer finding different things > > > > on different lisps, in the same shared library. > > > > > > Luis Olivera suggested using (foreign-symbol-pointer ... :data) instead > > > of (foreign-symbol-pointer ... :code), and it worked just fine, now > > > providing pointers to exactly same code! > > > > > > Apparently in the CMU/SBCL case i`ve been fed pointers to proc linkage > > > table entries or some lisp-specific trampolines. > > > > Is there any problem with getting different code? Using :data for code is > > not > > portable. > > Indeed -- sometimes the C code wants to be fed back pointers to its own > functions. As markers for setting up callbacks, for example. > > Also, i guess, the principle of least astonishment is applicable here -- > that is, a pointer to the function is a pointer to the function, after > all.
OK, I see. Beware that on some OSes, functions can have an internal entrypoint and multiple external entrypoints, so different modules can see different pointers to the same function even in C code. This should be OK for function pointer comparison as long as the the old and new values are read by the same module. __Martin _______________________________________________ cffi-devel mailing list cffi-devel@common-lisp.net http://common-lisp.net/cgi-bin/mailman/listinfo/cffi-devel
