Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Re: copy_from_user() fixu | Date | Tue, 25 Aug 1998 00:49:25 -0700 (PDT) |
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> H. Peter Anvin writes: > > > > > > Well, being serious here, I have a library that is bug-free, but I > > > can't depend on application writers to sustain my level of > > > perfection. So, so help these lesser beings, I trap EFAULT in my > > > library and yield a more meaningful diagnostic than a mere EFAULT or > > > SEGV. > > > > Now you *really* convinced me that you're crazy. > > Why not insult me further while you're at it?
You claimed you have a library that's bug-free, and you're relying on undefined behaviour. Clearly, your definition of "bug-free" is something different than us "lesser beings" use.
> > Once again: if you're relying on EFAULT rather than SIGSEGV, your code > > is broken, as you're relying on details of the libc/kernel interface. > > I would argue that *IS* a bug in your "bug-free" library. > > I'm relying on what I've seen written in man pages for all varieties > of Unix I've had access to.
Yes, it says that it's a PERMITTED return value, which is fundamentally different from GUARANTEED.
> This abstract libc/kernel interface you refer to is an abstraction > you've invented. It's not Unix practice. Unix practice is to return > EFAULT on system calls. System calls are open(2), read(2), write(2) > and similar.
I didn't invent it. It has been in every single Unix spec I've ever read, and it's very explicit.
> > If you want to trap errors, you either have to sanitize the input, or > > trap SIGSEGV. > > I can't sanitise the input: I don't know what pointer the application > will pass. Trapping SEGV is a performance bugger: I have to install a > signal handler before every pseudo-syscall and restore it afterwards > (my library can't steal signals).
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