Hi Joseph, On 12/30/22 22:08, Joseph Myers wrote:
On Fri, 30 Dec 2022, Cristian Rodríguez via Libc-alpha wrote:On Fri, Dec 30, 2022 at 3:15 PM Joseph Myers <joseph@xxxxxxxxxxxxxxxx> wrote:I expect to implement these functions in due course for glibc (not GCC, since these are library functions, with the usual requirements for definitions with external linkage, though most would also have inline header implementations based on existing longstanding built-in functions).Unless I am seriously missing something, the compiler is required to provide an implementation of them as it is a freestanding header..right ?"freestanding" versus "hosted" isn't the right distinction for which component in a (compiler + library) implementation provides which pieces any more. The actual distinction is closer to whether a feature involves library functions (with external linkage): if it does, it belongs in the library (glibc), whereas if a header doesn't involve such functions, it belongs in the compiler (GCC), along with the library support (in libgcc) for language features (i.e. library code that can be needed even by programs that don't include any standard library header or call any function from the standard library). My list of things to be done for C2x in GCC includes updating the GCC documentation (standards.texi) to reflect this: that is, to say that GCC provides the compiler part of a freestanding or hosted implementation, and library support for language features and headers not involving external linkage functions, to be used together with a corresponding library implementation - not that it's a freestanding implementation by itself. (It wasn't quite right for C11 either; GCC provides <stdatomic.h> and libatomic, and while there are a few atomic_* functions with external linkage, the bulk of the operations in <stdatomic.h> are only generic functions with no defined external-linkage functions underlying them, while it's been documented for a long time that a corresponding library is always needed to provided memcpy, memmove and memset as those may be generated from use of language features without being called explicitly by the user's code. But C2x makes it a lot more visible that the previously documented rule of thumb for where a feature goes is no longer appropriate.)
Why is this duplication of responsibility for libc functions? Why isn't there a smaller say libmem that provides a unique implementation for these memcpy(), memmove(), memset() functions, and both gcc and glibc (and even the kernel could, with static linking) depend on it?
Cheers, Alex -- <http://www.alejandro-colomar.es/>
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