[x86 folks in CC so that they can chime in on the precise rules for this stuff] Hi! I noticed that several makefiles under drivers/gpu/drm/amd/display/dc/ turn on floating-point instructions in the compiler flags (-mhard-float, -msse and -msse2) in order to make the "float" and "double" types usable from C code without requiring helper functions. However, as far as I know, code running in normal kernel context isn't allowed to use floating-point registers without special protection using helpers like kernel_fpu_begin() and kernel_fpu_end() (which also require that the protected code never blocks). If you violate that rule, that can lead to various issues - among other things, I think the kernel will clobber userspace FPU register state, and I think the kernel code can blow up if a context switch happens at the wrong time, since in-kernel task switches don't preserve FPU state. Is there some hidden trick I'm missing that makes it okay to use FPU registers here? I would try testing this, but unfortunately none of the AMD devices I have here have the appropriate graphics hardware... _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
