On Thu, 2022-07-14 at 09:30 +0100, Szabolcs Nagy wrote: > The 07/13/2022 12:55, David Malcolm wrote: > > On Wed, 2022-07-13 at 16:01 +0200, Florian Weimer wrote: > > > * David Malcolm: > > GCC trunk's -fanalyzer implements the new warnings via a state > > machine > > for file-descriptor values; it currently has rules for handling > > "open", > > "close", "read", and "write", and these functions are currently hard- > > coded inside the analyzer. > > > > Here are some examples on Compiler Explorer of what it can/cannot > > detect: > > https://godbolt.org/z/nqPadvM4f > > > > Probably the most important one IMHO is the leak detection. > > nice. > > > Would it be helpful to have some kind of attribute for "returns a new > > open FD"? Are there other ways to close a FD other than calling > > "close" on it? (Would converting that to some kind of "closes" > > attribute be a good idea?)
Thanks, lots of good ideas here; I've filed various RFEs about these; I'm posting the details below for reference. > > dup2(oldfd, newfd) > dup3(oldfd, newfd, flags) > > closes newfd (and also opens it to be a dup of oldfd) > unless the call fails. dup and friends probably need special-casing; I've filed this as: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106298 > > close_range(first, last, flags) close_range and closefrom would need special-casing, already filed as: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106283 > > fclose(fdopen(fd, mode)) The analyzer now attempts to track both file descriptors and stdio streams, so we probably need to special-case fdopen to capture the various possible interactions between these two leak detectors; I've filed this as: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106299 with an implementation idea there. > > but users can write all sorts of wrappers around close too. Yeah. If the -fanalyzer leak detectors see a value "escape" into unknown code, then they don't report leaks; see e.g.: https://godbolt.org/z/n8fMhGTP5 where we don't report in test_2 about fd leaking due to the call to: might_close (fd); which is extern, and so we conservatively assume that fd doesn't leak. > > > > > Are there any other "magic" values for file-descriptors we should be > > aware of? > > > > mmap may require fd==-1 for anonymous maps. mmap is its own can of worms, which I've filed as: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106301 You also reminded me that we need to track other ways in which the user could obtain an fd that could leak, which I've filed as: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106300 (covering creat, pipe and friends, dup and friends, fcntl, and socket). I've added all of these to the top-level RFE for -fanalyzer tracking file descriptors: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=analyzer-fd which is now a tracker-bug: https://gcc.gnu.org/bugzilla/showdependencytree.cgi?id=analyzer-fd Thanks again for the ideas Dave
