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> First of all, it is the OS ABI, in operating systems that happened to be written in C. It may be per-OS (I wouldn't try linking Linux and NT object files eve

> First of all, it is the OS ABI, in operating systems that happened to be written in C. It may be per-OS (I wouldn't try linking Linux and NT object files even if they were both compiled from C by GCC with matching versions and everything), but enough details come from C that I think it's fair to call it a C ABI. Like, I can write unix software in pascal, but in order to write to stdout that code is gonna have to convert pascal strings into C strings. OTOH, pascal binaries using pascal libraries can use pascal semantics even on an OS that uses C ABIs.

pjmlp 1y ago
Strings is the easy part. Try to link two binary libraries in Linux, both compiled with GCC, while not using exactly the same compiler flags, or the same data padding, for example things like structures. Since committee people can explain it even better, "To Save C, We Must Save ABI" https://thephd.dev/to-save-c-we-must-save-abi-fixing-c-function-abi https://thephd.dev/to-save-c-we-must-save-abi-fixing-c-funct...
- uecker 1y ago
  Sorry, this is nonsense. Binaries link just fine on Linux. If you use a compiler flag that changes the ABI, then you are on your own, of course, but the GCC docu makes it very clear which specific flags those are. There is some corner cases with problems where you get problems if you use different compilers, e.g. atomic alignment (by adopting the broken C++ design into C) and some other corner cases where compilers did things slightly different.
  - RossBencina 1y ago
    > e.g. atomic alignment (by adopting the broken C++ design into C) I would like to learn more about that. Do you mean this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65146 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65146
    - uecker 1y ago
      Things like this resulting in differnt alignment between Clang and GCC on x86_64 for _Atomic struct { char a[3]; }; See: https://godbolt.org/z/v5hsjhzj9 https://godbolt.org/z/v5hsjhzj9 The problem is that in C++ these atomics are library types, but in C they are built-in types which should have a clearly specified ABI. But the goal was to make them compatibility with C++ library types, which is a rather stupid idea, which pulls in even more problems.
  - pjmlp 1y ago
    Assuming you have control over all binaries. Exactly because one gets issues with multiple compilers is yet another prof why there isn't such thing as official C ABI.
    - uecker 1y ago
      There official platform ABIs. There are not called C ABIs though.

pjmlp 1y ago

Strings is the easy part. Try to link two binary libraries in Linux, both compiled with GCC, while not using exactly the same compiler flags, or the same data padding, for example things like structures. Since committee people can explain it even better, "To Save C, We Must Save ABI" https://thephd.dev/to-save-c-we-must-save-abi-fixing-c-function-abi https://thephd.dev/to-save-c-we-must-save-abi-fixing-c-funct...

uecker 1y ago
Sorry, this is nonsense. Binaries link just fine on Linux. If you use a compiler flag that changes the ABI, then you are on your own, of course, but the GCC docu makes it very clear which specific flags those are. There is some corner cases with problems where you get problems if you use different compilers, e.g. atomic alignment (by adopting the broken C++ design into C) and some other corner cases where compilers did things slightly different.
- RossBencina 1y ago
  > e.g. atomic alignment (by adopting the broken C++ design into C) I would like to learn more about that. Do you mean this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65146 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65146
  - uecker 1y ago
    Things like this resulting in differnt alignment between Clang and GCC on x86_64 for _Atomic struct { char a[3]; }; See: https://godbolt.org/z/v5hsjhzj9 https://godbolt.org/z/v5hsjhzj9 The problem is that in C++ these atomics are library types, but in C they are built-in types which should have a clearly specified ABI. But the goal was to make them compatibility with C++ library types, which is a rather stupid idea, which pulls in even more problems.
- pjmlp 1y ago
  Assuming you have control over all binaries. Exactly because one gets issues with multiple compilers is yet another prof why there isn't such thing as official C ABI.
  - uecker 1y ago
    There official platform ABIs. There are not called C ABIs though.