Hi Greg, On Wed, 2025-06-18 at 22:21 +1000, Greg Ungerer wrote: > > Could you please elaborate this a bit more, please? > > > > Coldfire is handled as a separate target via TARGET_COLDFIRE in GCC, so we > > would certainly be able to toggle the alignment settings independent of > > what's done on classic m68k. > > The net out is that it is the same gcc compiler, m68k-linux-gcc. > ColdFire just needs specific code generation via command line switches, > like -m5200 (or -m5206e or -m5307 or -mcfv4e, etc). This is the same way > you would specify 680x0 level - m68020, -m68030, etc.
Yes, but there is a TARGET_COLDFIRE macro as I mentioned above which could be used to trigger which alignment to use by default. I don't see how that would complicate things. > The bulk of the instruction set is the same. Asm code will look totally > familiar to anyone who knows m68k :-) One notable difference is that > there is a more limited set addressing modes for some instructions. True, but you won't be able to run any classic m68k binaries on ColdFire and the other way around, are you? > FWIW ColdFire currently uses the same ABI as all other m68k, so it uses > 2-byte alignment today. I know. And one user on the LKML has already demonstrated that his Coldfire board booted fine with buildroot set to 4 bytes alignment. > > In the Linux kernel, Coldfire is also a separate > > arch, so the alignment settings can also be handled there separately if > > necessary. > > ColdFire is not handled as a separate architecture in linux, it is just a > variant of m68k - so uses arch/m68k in the source. Well, it's a separate sub-architecture, similar to what's done for sh3/sh4 on sh or the various ARM flavors. My point was just that there is a way to separate classic m68k and Coldfire code if necessary. > > It's not really necessary to enforce this on Coldfire. However, since > > buildroot > > builds completely from source, it wouldn't even be a problem to change the > > alignment > > there as well. > > Yes, that is totally right in my experience. Certainly in my ColdFire work > it is pretty much always a build-everything approach via buildroot or similar. > I wouldn't think an ABI change would actually worry too many ColdFire uses, > they don't use distributions like debian on them. (I would love to hear from > anyone who does!). Thanks a lot for confirming this! Adrian -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer `. `' Physicist `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
