Hi David! On Mon, Apr 16, 2012 at 06:28:55PM +0100, Dr. David Alan Gilbert wrote: >* Steve McIntyre ([email protected]) wrote: >> Hi, >> >> I'm looking through the archive for packages using libffi. There's a >> problem with libffi and variadic functions that has been recently >> fixed - see >> >> http://lists.debian.org/debian-arm/2012/03/msg00108.html >> >> for more information. So far, we only expect symptoms to show up on >> armhf *but* it might be more widespread. Until recently, libffi didn't >> support variadic functions properly. That's now been fixed in libffi, >> but there's an extra API call necessary in places where variadics are >> used. > >Ah, you've picked up this fun one :-)
Yup, Marcus pointed it out to me and I've started tracking it again. :-) >As I remember most other archs 'get away with it' often >because they do silly things like pass values in registers and >on the stack and still offset the stack for the ones passed in >registers. I don't know if anyone has got around to doing >other backends other than armhf since I touched it, but >I think we knew there were some of the MIPS varients that could >do with it. Right. Are these the newer mips ABI variants like n32/n64, do you know? If so, I'm not so worried just yet! >> Looking at gcc-4.6 and gcc-4.7, I can see that the embedded copies of >> libffi are too old for this fix. I don't see a build-dep on >> libffi-dev, whish suggests that they're using these embedded copies >> rather than the system version. A couple of questions here: I'm >> curious why this is? If it's definitely necessary, could we update >> those embedded copies to a more recent libffi with the change >> included? >> >> Even beyond that, there are quite likely to be changes that would need >> to be made in the gcc source to use the new ffi_prep_cif_var() >> function. My scan of the archive shows ffi_prep_cif() shows up / is >> used in: >> >> gcc-4.6 >> gcc-snapshot >> gcj-4.[467] >> >> at least. Can you help please? > >However, it's pretty rare for things to actually use variadics with >libffi, it's even rarer for them to pass floats; although someone had >asked for libffi to be fixed for armhf, I could never find someone to >say what app was broken; there were some mumblings about Java, but even >there I didn't actually find someone with a test. I think some Python >ctype examples looked broken. Yes, I've seen that too. >The other nasty to keep in mind is that where the libffi >calls come from some scripting language glue, it's not clear >that the languages/glue have the syntax to express that they're calling >a variadic function, so it might need language changes. >(I never managed to get any response out of the CType list). Yes. I looked for a response to your original mail there and couldn't find any in list archives; I'm guessing that's because you didn't get one? The Haskell packages that showed up in my scan of the Debian archive are apparently all OK; ghc has a habit of embedding large chunks of the core in everything it builds, and the ffi calls there are expected to be safe (no variadics). Otherwise, as you say: I'm looking at a number of language implementations where it's (a) not clear if they'll ever do variadics (b) if they *might* use variadics, it'll be because somebody is calling through a generic helper function with no current way of determining if the callee is variadic or not. Yay... :-/ -- Steve McIntyre, Cambridge, UK. [email protected] Who needs computer imagery when you've got Brian Blessed? -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: http://lists.debian.org/[email protected]
