That is almost surely it, thanks for the second pair of eyes. I had similar issues with a different type that I thought was a pointer but was actually a struct, but that one I couldn't even get a single call to work so it was much more obvious something was up.
On Sun, Sep 28, 2014 at 11:08 AM, Matthew Flatt <mfl...@cs.utah.edu> wrote: > Looking at > > http://clang.llvm.org/doxygen/CXString_8h_source.html > > it seems that CXString as returned by clang_getCursorSpelling() is not > a pointer: > > typedef struct { > const void *data; > unsigned private_flags; > } CXString; > > If that's right, I'm a little surprised that `cursor-spelling` works > --- but when you get representation wrong, strange things can happen, > including something working when it shouldn't. > > Am I looking at the right library/definitions? > > At Sun, 28 Sep 2014 10:48:06 -0700, Eric Dobson wrote: >> I'm trying to debug an FFI crash that I'm seeing, and because it is >> dealing with C code the error just presents as a segfault. I believe I >> have tracked down what is causing the problem, but don't understand >> how it could be doing so. >> >> I have two racket functions which take a "cursor" (the foreign >> libraries object) and return a string representation of it, which I'm >> trying to use for debugging. >> >> (define raw-clang-get-cstring >> (get-ffi-obj "clang_getCString" lib-clang >> (_fun _pointer -> _string))) >> >> (define raw-cursor-spelling >> (get-ffi-obj "clang_getCursorSpelling" lib-clang >> (_fun _CXCursor -> _pointer))) >> >> (define (cursor-spelling c) >> (raw-clang-get-cstring (raw-cursor-spelling c))) >> >> (define cursor-spelling2 >> (get-ffi-obj "clang_getCursorSpelling" lib-clang >> (_fun _CXCursor -> (make-ctype _pointer values (λ (v) >> (raw-clang-get-cstring v)))))) >> >> If I use cursor-spelling, I have not been able to trigger a crash. But >> if I use cursor-spelling2 I can reliably trigger a crash. >> >> Is there anything obvious on how these functions are different? >> Because they look to me like they should be doing the same thing. If >> it would be helpful I can try to get my code in a portable enough >> shape so that it will work/crash on another machine. >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
