7 ms·

Demangling C++ Symbols in Rust

245 points by andrew3726 10y ago

kbenson 10y ago
Tom Tromey, a GNU hacker and buddy of mine, mentioned that historically, the canonical C++ demangler in libiberty (used by c++filt and gdb) has had tons of classic C bugs: use-after-free, out-of-bounds array accesses, etc, and that it falls over immediately when faced with a fuzzer. In fact, there were so many of these issues that gdb went so far as to install a signal handler to catch SIGSEGVs during demangling. It “recovered” from the segfaults by longjmping out of the signal handler and printing a warning message before moving along and pretending that nothing happened. My ears perked up. Those are the exact kinds of things Rust protects us from at compile time! A robust alternative might actually be a boon not just for the Rust community, but everybody who wants to demangle C++ symbols. Then, later: Additionally, I’ve been running American Fuzzy Lop (with afl.rs) on cpp_demangle overnight. It found a panic involving unhandled integer overflow, which I fixed. Since then, AFL hasn’t triggered any panics, and its never been able to find a crash (thanks Rust!) so I think cpp_demangle is fairly solid and robust. That's what I like to see. Targeted useful reimplementations in Rust that play well to its strengths. In this case, as a double benefit to both the Rust ecosystem and to anyone that wants a robust demangling library.
problems 10y ago
How bad are the rules for MSVC compared to the Itanium ones and would you consider adding support for it too? Not that I have a use case in mind or anything, just curious.
- kryptiskt 10y ago
  The Microsoft name mangling scheme is explained in Agner Fog's PDF on calling conventions: http://www.agner.org/optimize/calling_conventions.pdf http://www.agner.org/optimize/calling_conventions.pdf
  - cokernel_hacker 10y ago
    That's really only a fraction of it. The only definitive documentation that I know of is clang's implementation of its mangling scheme: https://github.com/llvm-mirror/clang/blob/master/lib/AST/MicrosoftMangle.cpp https://github.com/llvm-mirror/clang/blob/master/lib/AST/Mic...
- jcranmer 10y ago
  Pretty bad, actually. There is no official documentation of the name mangling, so everything that is known is reverse engineered. In particular, there are outright bugs in the name mangling scheme, and one of the rules appears to rely on hashing the function body to produce a result. I'd give you examples, but, I don't have any of them on hand (I'm mostly relying on recollection from conversations with David Majnemer).
  - twoodfin 10y ago
    one of the rules appears to rely on hashing the function body to produce a result Gross! I wonder what that's for. Somebody's hack to allow same-name/same-interface header inline functions to coexist?
jjoonathan 10y ago
> These days, almost every C++ compiler uses the Itanium C++ ABI’s name mangling rules. The notable exception is MSVC, which uses a completely different format. You stay classy, Microsoft. > Its not just the grammar that’s huge, the symbols themselves are too. Here is a pretty big mangled C++ symbol from SpiderMonkey [...] That’s 355 bytes! Here's a >4kB symbol I encountered while liberating some ebooks from an abandoned DRM app: tetraphilia::transient_ptrs<tetraphilia::imaging_model::PixelProducer<T3AppTraits> >::ptr_type tetraphilia::imaging_model::MakeIdealPixelProducer<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 0ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> > > >, tetraphilia::Terminal> >, T3AppTraits, tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, tetraphilia::imaging_model::SeparableOperation<tetraphilia::imaging_model::ClipOperation<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > > >(tetraphilia::ArgType<tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 0ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> > > >, tetraphilia::Terminal> > > >, T3AppTraits::context_type&, tetraphilia::imaging_model::Constraints<T3AppTraits> const&, tetraphilia::imaging_model::SeparableOperation<tetraphilia::imaging_model::ClipOperation<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > >, tetraphilia::imaging_model::const_GraphicYWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > const*, tetraphilia::imaging_model::const_GraphicYWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > const*, tetraphilia::imaging_model::const_GraphicYWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > const*, tetraphilia::imaging_model::SegmentFactory<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >*)
pjmlp 10y ago
> Linkers only support C identifiers for symbol names. This is only true of UNIX system linkers, before the FOSS and UNIX clones wave, it was common for each compiler to have its own language specific linker.
- Rusky 10y ago
  Kind of a blessing and a curse- reduces links to a common subset of functionality, but also makes it trivial to link together code from any languages that support the platform's C ABI.
nly 10y ago
LLVMs libcxxabi has a demangler which doesn't have the worst looking code in the world[0], has no external dependencies (outside of the C++ standard library), has lately been fuzzed[1] and is tested[2]. Switching languages is cool, but the Rust code is actually longer and still uses a hand written parser, so how can you be sure it is any more correct or won't eat all your memory? [0] http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_demangle.cpp?revision=293638&view=markup http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_... [1] http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/fuzz/cxa_demangle_fuzzer.cpp?revision=290650&view=markup http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/fuzz/cxa... [2] http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/test_demangle.pass.cpp?revision=293638&view=markup http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/tes...
- simcop2387 10y ago
  The best way is to make sure it's correct to every test case you can find. I.e. include the test s you point to there along with the tests from libiberty etc. That'll at least let you say that's it's as provably correct as the others. The next advantage is going to be that Rust helps prevent certain classes of bugs (in this case memory issues) as long as you're not doing unsafe{} things. And while that rests on Rust's ability to prove that it's a step up from not having that. The handwritten parser doesn't mean much in the advent of testing against a wide array of inputs, if it was parsing incorrectly then it's not going to pass the tests. Sure there might be an edge case where it just recurses but that's also the case of libcxxabi and the others. The code being longer also means basically nothing. It just means that either the code is more verbose or could be shortened somehow it says nothing about it's correctness or viability.
- roca 10y ago
  It's true that one can't be sure the Rust version is "any more correct and won't eat all your memory". However, an even more important question is how many exploitable bugs remain in the LLVM library vs the Rust library. The data suggests that the answer for Rust is zero but the answer for LLVM is greater than zero.
  - 10y ago
shmerl 10y ago
Can it help to implement C++ bindings for Rust?
- steveklabnik 10y ago
  My understanding is that yes, this is part of that puzzle. The author of this post works on https://crates.io/crates/bindgen https://crates.io/crates/bindgen
sfink 10y ago
Coincidentally, I recently discovered that code I landed in the mozilla repo a couple of weeks ago crashes gdb when it tries to demangle (and c++filt on the command line). Looks to be infinite recursion. It's still in the current Nightly binary. _ZN2js18CompartmentChecker5checkIN2JS8GCVectorI4jsidLm0ENS_15TempAllocPolicyEEEEEN7mozilla8EnableIfIXsrNS7_6IsSameIDTclptcvPT_LDn0E5beginEEDTclptcvSB_LDn0E3endEEEE5valueEvE4TypeERKSA_ coming from template <typename Container> typename mozilla::EnableIf< mozilla::IsSame< decltype(((Container*)nullptr)->begin()), decltype(((Container*)nullptr)->end()) >::value >::Type check(const Container& container) { ... }
- ayosec 10y ago
  Out of curiosity, what version of c++filt are you using? I tried with 2.27.51 (Debian), and it works: mozilla::EnableIf<mozilla::IsSame<decltype ((((JS::GCVector<jsid, 0ul, js::TempAllocPolicy>*)((decltype(nullptr))0))->begin)()), decltype ((((JS::GCVector<jsid, 0ul, js::TempAllocPolicy>*)((decltype(nullptr))0))->end)())>::value, void>::Type js::CompartmentChecker::check<JS::GCVector<jsid, 0ul, js::TempAllocPolicy> >(JS::GCVector<jsid, 0ul, js::TempAllocPolicy> const&)
  - sfink 10y ago
    2.26.1-1.fc25 from Fedora 25
bassamtabbara 10y ago
There's also this one https://github.com/ianlancetaylor/demangle https://github.com/ianlancetaylor/demangle
phkahler 10y ago
I really enjoy reading these pieces where someone rewrites something in rust and it turns out better than the old C version due to rusts safety features. Usually those kinds of projects are just a rewrite to someones favorite language of the month, for little tangible benefit other than their own satisfaction or education. These rust ones seem to show tangible benefits to the language itself.

245 points by andrew3726 10y ago

Tom Tromey, a GNU hacker and buddy of mine, mentioned that historically, the canonical C++ demangler in libiberty (used by c++filt and gdb) has had tons of classic C bugs: use-after-free, out-of-bounds array accesses, etc, and that it falls over immediately when faced with a fuzzer. In fact, there were so many of these issues that gdb went so far as to install a signal handler to catch SIGSEGVs during demangling. It “recovered” from the segfaults by longjmping out of the signal handler and printing a warning message before moving along and pretending that nothing happened. My ears perked up. Those are the exact kinds of things Rust protects us from at compile time! A robust alternative might actually be a boon not just for the Rust community, but everybody who wants to demangle C++ symbols. Then, later: Additionally, I’ve been running American Fuzzy Lop (with afl.rs) on cpp_demangle overnight. It found a panic involving unhandled integer overflow, which I fixed. Since then, AFL hasn’t triggered any panics, and its never been able to find a crash (thanks Rust!) so I think cpp_demangle is fairly solid and robust. That's what I like to see. Targeted useful reimplementations in Rust that play well to its strengths. In this case, as a double benefit to both the Rust ecosystem and to anyone that wants a robust demangling library.

problems 10y ago

How bad are the rules for MSVC compared to the Itanium ones and would you consider adding support for it too? Not that I have a use case in mind or anything, just curious.

kryptiskt 10y ago
The Microsoft name mangling scheme is explained in Agner Fog's PDF on calling conventions: http://www.agner.org/optimize/calling_conventions.pdf http://www.agner.org/optimize/calling_conventions.pdf
- cokernel_hacker 10y ago
  That's really only a fraction of it. The only definitive documentation that I know of is clang's implementation of its mangling scheme: https://github.com/llvm-mirror/clang/blob/master/lib/AST/MicrosoftMangle.cpp https://github.com/llvm-mirror/clang/blob/master/lib/AST/Mic...
jcranmer 10y ago
Pretty bad, actually. There is no official documentation of the name mangling, so everything that is known is reverse engineered. In particular, there are outright bugs in the name mangling scheme, and one of the rules appears to rely on hashing the function body to produce a result. I'd give you examples, but, I don't have any of them on hand (I'm mostly relying on recollection from conversations with David Majnemer).
- twoodfin 10y ago
  one of the rules appears to rely on hashing the function body to produce a result Gross! I wonder what that's for. Somebody's hack to allow same-name/same-interface header inline functions to coexist?

jjoonathan 10y ago

> These days, almost every C++ compiler uses the Itanium C++ ABI’s name mangling rules. The notable exception is MSVC, which uses a completely different format. You stay classy, Microsoft. > Its not just the grammar that’s huge, the symbols themselves are too. Here is a pretty big mangled C++ symbol from SpiderMonkey [...] That’s 355 bytes! Here's a >4kB symbol I encountered while liberating some ebooks from an abandoned DRM app: tetraphilia::transient_ptrs<tetraphilia::imaging_model::PixelProducer<T3AppTraits> >::ptr_type tetraphilia::imaging_model::MakeIdealPixelProducer<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 0ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> > > >, tetraphilia::Terminal> >, T3AppTraits, tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, tetraphilia::imaging_model::SeparableOperation<tetraphilia::imaging_model::ClipOperation<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > > >(tetraphilia::ArgType<tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 0ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::OneXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 0ul> > > >, tetraphilia::TypeList<tetraphilia::imaging_model::XWalkerCluster<tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalkerList3<tetraphilia::imaging_model::const_UnifiedGraphicXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits>, 0ul, 0, 1ul, 0ul, 0, 0ul, 0ul, 0, 0ul, 1ul>, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> >, tetraphilia::imaging_model::GraphicXWalker<tetraphilia::imaging_model::const_IgnoredRasterXWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 0ul, 0, 1ul, 1ul>, tetraphilia::imaging_model::const_SpecializedRasterXWalker<unsigned char, 2ul, -1, 3ul, 3ul> > > >, tetraphilia::Terminal> > > >, T3AppTraits::context_type&, tetraphilia::imaging_model::Constraints<T3AppTraits> const&, tetraphilia::imaging_model::SeparableOperation<tetraphilia::imaging_model::ClipOperation<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > >, tetraphilia::imaging_model::const_GraphicYWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > const*, tetraphilia::imaging_model::const_GraphicYWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > const*, tetraphilia::imaging_model::const_GraphicYWalker<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> > const*, tetraphilia::imaging_model::SegmentFactory<tetraphilia::imaging_model::ByteSignalTraits<T3AppTraits> >*)

pjmlp 10y ago

> Linkers only support C identifiers for symbol names. This is only true of UNIX system linkers, before the FOSS and UNIX clones wave, it was common for each compiler to have its own language specific linker.

Rusky 10y ago
Kind of a blessing and a curse- reduces links to a common subset of functionality, but also makes it trivial to link together code from any languages that support the platform's C ABI.

nly 10y ago

LLVMs libcxxabi has a demangler which doesn't have the worst looking code in the world[0], has no external dependencies (outside of the C++ standard library), has lately been fuzzed[1] and is tested[2]. Switching languages is cool, but the Rust code is actually longer and still uses a hand written parser, so how can you be sure it is any more correct or won't eat all your memory? [0] http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_demangle.cpp?revision=293638&view=markup http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_... [1] http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/fuzz/cxa_demangle_fuzzer.cpp?revision=290650&view=markup http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/fuzz/cxa... [2] http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/test_demangle.pass.cpp?revision=293638&view=markup http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/test/tes...

simcop2387 10y ago
The best way is to make sure it's correct to every test case you can find. I.e. include the test s you point to there along with the tests from libiberty etc. That'll at least let you say that's it's as provably correct as the others. The next advantage is going to be that Rust helps prevent certain classes of bugs (in this case memory issues) as long as you're not doing unsafe{} things. And while that rests on Rust's ability to prove that it's a step up from not having that. The handwritten parser doesn't mean much in the advent of testing against a wide array of inputs, if it was parsing incorrectly then it's not going to pass the tests. Sure there might be an edge case where it just recurses but that's also the case of libcxxabi and the others. The code being longer also means basically nothing. It just means that either the code is more verbose or could be shortened somehow it says nothing about it's correctness or viability.
roca 10y ago
It's true that one can't be sure the Rust version is "any more correct and won't eat all your memory". However, an even more important question is how many exploitable bugs remain in the LLVM library vs the Rust library. The data suggests that the answer for Rust is zero but the answer for LLVM is greater than zero.
- 10y ago

shmerl 10y ago

Can it help to implement C++ bindings for Rust?

steveklabnik 10y ago
My understanding is that yes, this is part of that puzzle. The author of this post works on https://crates.io/crates/bindgen https://crates.io/crates/bindgen

sfink 10y ago

Coincidentally, I recently discovered that code I landed in the mozilla repo a couple of weeks ago crashes gdb when it tries to demangle (and c++filt on the command line). Looks to be infinite recursion. It's still in the current Nightly binary. _ZN2js18CompartmentChecker5checkIN2JS8GCVectorI4jsidLm0ENS_15TempAllocPolicyEEEEEN7mozilla8EnableIfIXsrNS7_6IsSameIDTclptcvPT_LDn0E5beginEEDTclptcvSB_LDn0E3endEEEE5valueEvE4TypeERKSA_ coming from template <typename Container> typename mozilla::EnableIf< mozilla::IsSame< decltype(((Container*)nullptr)->begin()), decltype(((Container*)nullptr)->end()) >::value >::Type check(const Container& container) { ... }

ayosec 10y ago
Out of curiosity, what version of c++filt are you using? I tried with 2.27.51 (Debian), and it works: mozilla::EnableIf<mozilla::IsSame<decltype ((((JS::GCVector<jsid, 0ul, js::TempAllocPolicy>*)((decltype(nullptr))0))->begin)()), decltype ((((JS::GCVector<jsid, 0ul, js::TempAllocPolicy>*)((decltype(nullptr))0))->end)())>::value, void>::Type js::CompartmentChecker::check<JS::GCVector<jsid, 0ul, js::TempAllocPolicy> >(JS::GCVector<jsid, 0ul, js::TempAllocPolicy> const&)
- sfink 10y ago
  2.26.1-1.fc25 from Fedora 25

bassamtabbara 10y ago

There's also this one https://github.com/ianlancetaylor/demangle https://github.com/ianlancetaylor/demangle

phkahler 10y ago

I really enjoy reading these pieces where someone rewrites something in rust and it turns out better than the old C version due to rusts safety features. Usually those kinds of projects are just a rewrite to someones favorite language of the month, for little tangible benefit other than their own satisfaction or education. These rust ones seem to show tangible benefits to the language itself.