> Author: mmacy > Date: Mon Jul 2 19:48:38 2018 > New Revision: 335873 > URL: > https://svnweb.freebsd.org/changeset/base/335873 > > > Log: > inline atomics and allow tied modules to inline locks > > - inline atomics in modules on i386 and amd64 (they were always > inline on other arches) > - allow modules to opt in to inlining locks by specifying > MODULE_TIED=1 in the makefile
I recently found the following about ABI incompatibilities between clang and gcc relative to C11 language based atomics: https://bugs.llvm.org/show_bug.cgi?id=26462 26462 – GCC/clang C11 _Atomic incompatibility So are there implications about building the kernel vs. modules that overall mix the toolchains once modules are loaded? Do the toolchains need to match, at least for amd64 and i386 TARGET_ARCH 's? For reference as an introduction to the material in llvm's 26462 . . . It appears that the normal source of platform ABI definitions are not explicit/detailed in the area and allow for incompatibilities in this area. clang and gcc made differing choices absent being constrained to match. An example (a powerpc64 context was indicated): struct A16 { char val[16]; }; _Atomic struct A16 a16; // GCC: _Static_assert(_Alignof(a16) == 16, ""); // Clang: _Static_assert(_Alignof(a16) == 1, ""); Non-power-of-2 is a general problem (not a powerpc64 context from what I can tell): struct A3 { char val[3]; }; _Atomic struct A3 a3; // GCC: _Static_assert(sizeof(a3) == 3, ""); _Static_assert(_Alignof(a3) == 1, ""); // Clang: _Static_assert(sizeof(a3) == 4, ""); _Static_assert(_Alignof(a3) == 4, ""); Comment 6 (by John McCall) is relevant: QUOTE Anyway, while I prefer the Clang rule, the GCC rule is defensible, as are any number of other rules. The important point, however, is that having this discussion is not the right approach to solving this problem. The layout of _Atomic(T) is ABI. ABI rules are not generally determined by compiler implementors making things up as they go along, or at least they shouldn't be. The Darwin ABI for _Atomic is the rule implemented in Clang, which we actually did think about carefully when we adopted it. Other platforms need to make their own call, and it probably shouldn't just be "whatever's implemented in GCC", especially on other platforms where GCC is not the system compiler. END QUOTE === Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar) _______________________________________________ freebsd-amd64@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-amd64 To unsubscribe, send any mail to "freebsd-amd64-unsubscr...@freebsd.org"
