4 ms·

However this doesn't proove that clang produce error-free (was afar the compiklation goes) executables.

by frownie 15y ago

stingraycharles 15y ago
No one can ever prove such a thing. Neither can it be proven that gcc or any compiler for that matter produces error-free executables. What this does, however, is providing information and analysis about the quality of the clang compilation process as compared to gcc.
- ars 15y ago
  No can prove it, but at least the GCC version are actually run by people - these version and created, but never actually used. He should do some fuzz testing of these programs, with the exact same fuzz sent to the GCC versions, and then report any differences. But collecting the "results" would be hard - it's not always visible in output, you'd have to track system calls and IO.
  - rbanffy 15y ago
    The ideal scenario would be if upstream projects provided embedded test code with standardized hooks so that tests could be built, executed and results collected in an automated way. Even if we started with a small test set for some projects, it would be a huge win in the long run just to have this scaffolding in place. Any ideas on how to make a distro-agnostic testing hook?
    - johnpaulett 15y ago
      It does not necessarily have to be distro-agnostic. Debian packages can already hook the upstream's test suite (e.g. via dh_auto_test). From my (extremely limited and mostly dynamic language) Debian packaging experience, it seems that more often than not, packages do not use this existing hook. Not sure why that is though.
  - aidenn0 15y ago
    As an example, gcc generates nearly unusable code for a Via Isaiah in amd64 mode if you compile with -O1, and this has apparently been a known issue for at least 2 years.
- iso8859-1 15y ago
  It can be proven, see CompCert C compiler: http://compcert.inria.fr/compcert-C.html http://compcert.inria.fr/compcert-C.html.
  - stingraycharles 15y ago
    That only proves that a compiler behaves according to a language definition. That does not prove the executables will behave as you expect the executables to behave, and thus there is no way knowing the executables will be error free.
    - Dylan16807 15y ago
      Frownie said error-free compilation, not error-free in all possible aspects.
frownie 15y ago
Opps, type : : "(as far as the compilation goes)"
abc_lisper 15y ago
Doesn't Apple use clang for OS X? If it does, that's as good a validation as any for me.
- gtufano 15y ago
  Another (IMHO better) validation is that FreeBSD compiles the kernel with clang: http://wiki.freebsd.org/BuildingFreeBSDWithClang http://wiki.freebsd.org/BuildingFreeBSDWithClang
  - vertex-four 15y ago
    FreeBSD can compile the kernel with Clang, but at least as of 9.0-RELEASE, the default is still GCC. They're aiming to switch to Clang for as much as possible for 10.0-RELEASE, in a couple of years.
  - emaste 15y ago
    FreeBSD has made a lot of progress with clang in the base system (which consists of both the kernel and standard userland); I run a clang-compiled FreeBSD on my laptop. But that said, we have a lot more clang coverage through the work done by the ports team who have been running experimental builds with clang for more than a year. That work is documented here: http://wiki.freebsd.org/PortsAndClang http://wiki.freebsd.org/PortsAndClang
- smackfu 15y ago
  Isn't most of their code in Objective C? Does that use clang too?
  - gregheo 15y ago
    clang does support Objective C (as does gcc). Apple does look after a lot of plain old C (e.g. Core Foundation) and C++ (e.g. WebKit) too, so clang handles all three.
    - malkia 15y ago
InclinedPlane 15y ago
And? Nobody expects that gcc, or intel's reference compilers, or Microsoft's compilers produce provably correct output. How could they? The C standard contains ambiguity in several areas.

However this doesn't proove that clang produce error-free (was afar the compiklation goes) executables.

by frownie 15y ago

However this doesn't proove that clang produce error-free (was afar the compiklation goes) executables.

No one can ever prove such a thing. Neither can it be proven that gcc or any compiler for that matter produces error-free executables. What this does, however, is providing information and analysis about the quality of the clang compilation process as compared to gcc.

ars 15y ago
No can prove it, but at least the GCC version are actually run by people - these version and created, but never actually used. He should do some fuzz testing of these programs, with the exact same fuzz sent to the GCC versions, and then report any differences. But collecting the "results" would be hard - it's not always visible in output, you'd have to track system calls and IO.
- rbanffy 15y ago
  The ideal scenario would be if upstream projects provided embedded test code with standardized hooks so that tests could be built, executed and results collected in an automated way. Even if we started with a small test set for some projects, it would be a huge win in the long run just to have this scaffolding in place. Any ideas on how to make a distro-agnostic testing hook?
  - johnpaulett 15y ago
    It does not necessarily have to be distro-agnostic. Debian packages can already hook the upstream's test suite (e.g. via dh_auto_test). From my (extremely limited and mostly dynamic language) Debian packaging experience, it seems that more often than not, packages do not use this existing hook. Not sure why that is though.
- aidenn0 15y ago
  As an example, gcc generates nearly unusable code for a Via Isaiah in amd64 mode if you compile with -O1, and this has apparently been a known issue for at least 2 years.
iso8859-1 15y ago
It can be proven, see CompCert C compiler: http://compcert.inria.fr/compcert-C.html http://compcert.inria.fr/compcert-C.html.
- stingraycharles 15y ago
  That only proves that a compiler behaves according to a language definition. That does not prove the executables will behave as you expect the executables to behave, and thus there is no way knowing the executables will be error free.
  - Dylan16807 15y ago
    Frownie said error-free compilation, not error-free in all possible aspects.

frownie 15y ago

Opps, type : : "(as far as the compilation goes)"

abc_lisper 15y ago

Doesn't Apple use clang for OS X? If it does, that's as good a validation as any for me.

gtufano 15y ago
Another (IMHO better) validation is that FreeBSD compiles the kernel with clang: http://wiki.freebsd.org/BuildingFreeBSDWithClang http://wiki.freebsd.org/BuildingFreeBSDWithClang
- vertex-four 15y ago
  FreeBSD can compile the kernel with Clang, but at least as of 9.0-RELEASE, the default is still GCC. They're aiming to switch to Clang for as much as possible for 10.0-RELEASE, in a couple of years.
- emaste 15y ago
  FreeBSD has made a lot of progress with clang in the base system (which consists of both the kernel and standard userland); I run a clang-compiled FreeBSD on my laptop. But that said, we have a lot more clang coverage through the work done by the ports team who have been running experimental builds with clang for more than a year. That work is documented here: http://wiki.freebsd.org/PortsAndClang http://wiki.freebsd.org/PortsAndClang
smackfu 15y ago
Isn't most of their code in Objective C? Does that use clang too?
- gregheo 15y ago
  clang does support Objective C (as does gcc). Apple does look after a lot of plain old C (e.g. Core Foundation) and C++ (e.g. WebKit) too, so clang handles all three.
  - malkia 15y ago

InclinedPlane 15y ago

And? Nobody expects that gcc, or intel's reference compilers, or Microsoft's compilers produce provably correct output. How could they? The C standard contains ambiguity in several areas.