Date: Tue, 17 Nov 2015 22:15:29 +0000 From: Petr Hosek <phosek@...omium.org> To: musl@...ts.openwall.com Subject: Re: Support for out-of-tree build Absolutely, that's probably the simplest solution in the sense that it avoids using additional .mk/.sub files or complicated build-time logic. If that's the solution we all agree on, I'd be happy to implement this as a separate patch and then rebase the out-of-tree build patch on top of that. On Tue, Nov 17, 2015 at 2:01 PM Rich Felker <dalias@...c.org> wrote: > On Tue, Nov 17, 2015 at 09:37:37PM +0000, Petr Hosek wrote: > > How would you express the fact that e.g. armhf subarch should use armel > > implementation of memcpy.s? > > The point of the *.sub files is to define a mapping from a fully > specific subarch (with 'default'/'empty' replaced with an explicit > default; this is why configure sets ASMSUBARCH=el for plain arm) to > the actual file to use, which is almost always going ot be shared > between a number of subarchs when there's more than one 'dimension' > involved. > > However there's no need for this mapping to be defined per-file. In > reality it's sufficient to have a fixed fallback sequence. In the rare > case where there were asm files that depended on endianness and > hard/soft float in the same file, the fallback order would look > something like (for le-hf): > > le-hf le-any any-hf any-any > > But for our actual usage cases it suffices just to have: > > le hf any > > However, at this point I'm strongly considering whether we should just > do away with the subarch dirs entirely and use preprocessed asm or C > with inline asm in their place. The one place this is mildly difficult > is when only some of the subarchs want the asm at all, and others want > the generic C. This is common for fenv.s and also applies to arm > memcpy.s where we lack a big-endian variant. > > One possible solution would be to have (for example) > src/string/arm/memcpy.c that just does > > #ifdef __ARMEB__ > #include <../memcpy.c> > #endif > > and then put memcpy.S in arch/arm/src/ with #ifndef __ARMEB__ around > the whole file. > > That would fully eliminate the subarch mess from the build system and > leave us with a fixed fallback order for it to use: > > $(ARCH)/%.S > $(ARCH)/%.s > $(ARCH)/%.c > %.S > %.s > %.c > > Currently the unadorned %.S/%.s is not needed, but I would consider > adding it so we can put asm files in arch/$(ARCH)/src without needing > dummy .c files for them to pull in asm from arch/$(ARCH)/src/$(ARCH). > > Would this make things simpler for the build system? I think so. > > Rich > Content of type "text/html" skipped
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