On 02 Sep 2015, at 02:08, Rich Felker <dal...@libc.org> wrote: > On Wed, Sep 02, 2015 at 01:24:55AM +0900, Oleg Endo wrote: >>> I'm not sure what the best way to achieve multiple goals is, but the >>> current behavior makes it so you need --isa=any (and a final binary >>> with weird ABI tag) to have a binary that supports atomic operations >>> on any SH model. musl libc already has such support (except the new J2 >>> CAS instruction) and I would like to eventually provide a libatomic >>> approach for GCC too so that it's possible to use __sync/C11 atomics >>> and have the binary be safe to run on any model that supports the >>> baseline ISA & ABI you built for (e.g. all >=SH2 if you used -m2). >> >> I don't know the details of your implementation. The compiler >> generated atomic sequences are not really compatible. The safest >> thing is not to enable any atomic model in GCC and let it emit >> function calls to __atomic*. > > Exactly -- but then, libatomic.a needs to contain J2-specific cas.l > opcodes and SH4A-specific movli.l/movco.l opcodes and code that > selects at runtime which to use (or whether to use imask or gusa) > based on hwcap, etc. The point is that a mix of opcodes for different > ISA levels end up being in the final binary, which might otherwise be > targeted for SH-2 baseline so it can run on any of them. > >>> I have a patch for that part, just not expanding the >>> already-very-complex SH "family-tree" of instruction support. However >>> it's likely that encoding details will change (the draft encoding >>> overlaps with something used by SH2A IIRC, and the intent was not to >>> have such overlap) >> >> Yeah, it overlaps with the first 16 bit word of the 32 bit SH2A >> load/store insns. >> >>> so I'm holding off on submitting it until the >>> hardware side works out this issue. >> >> Sounds reasonable. > > In the mean time, do you have any suggestsions on how the ISA level > stuff should be done to add J2 on the binutils side?
Let's continue this topic on the binutils list ( https://sourceware.org/ml/binutils/2015-09/msg00031.html )
