Re: [PATCH] MIPS: Add emulation for fpureg-mem unaligned access
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Hello Maciej, On Wed, Jul 11, 2012 at 01:05:04AM +0100, Maciej W. Rozycki wrote: > On Wed, 20 Jun 2012, Lluís Batlle i Rossell wrote: > > > > > Well, I think I take my words back. Handling the ldc1/sdc1 cases in MIPS32 is > > > > tricker than I thought first, because I can't use ldl/ldr or sdl/sdr there. > > > > Given my ability with mips assembly, I leave the patch as is. > I suggest that for 32-bit kernels you simply reuse the existing snippets > from that function and handle ldc1/sdc1 with a pair of lwl/ldr or swl/swr > pairs ordered as appropriate for the endianness selected -- that should be > fairly easy. Hm I still don't understand well enough how to do that. Would I need to get some aligned memory (a stack automatic variable for example), copy the double word there with proper endianness, and then call again ldc1? (similar for sdc1) > Also regardless of that, please make sure that your code handles the two > possible settings of CP0 Status register's bit FR correctly, as the 32-bit > halves of floating-point data are distributed differently across > floating-point registers based on this bit's setting (check if an o32 and > an n64 or n32 program gets these values right). Hm I'm failing to find in the mips-iv.pdf how to check that FR bit, although I see it mentioned there. Sorry. > > As Jonas reported, I think that maybe I should rework the patch for it to emit > > sigbus instead of sigill on ldc1,ldc1 for mips32. Do I understand it right? > > Have you checked your code against a non-FPU processor (or with the > "nofpu" kernel option) too? No. Would in that case the processor have the fpu disabled? I understand that the code path is called only in a particular case of 'unaligned access' exception. Thank you for your comments. Regards, Lluís.
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