> + /* Avoid inadvertently triggering emulation */ > + if ((value & PR_FP_MODE_FR) && cpu_has_fpu && > + !(current_cpu_data.fpu_id & MIPS_FPIR_F64)) > + return -EOPNOTSUPP; > + if ((value & PR_FP_MODE_FRE) && !cpu_has_fre) > + return -EOPNOTSUPP; This is perhaps not important immediately but these two cases can be seen as inconsistent. I.e. FR1 is emulated if there is no FPU but FRE is not emulated if there is no FPU. I believe this would be more consistent: if ((value & PR_FP_MODE_FRE) && cpu_has_fpu && !cpu_has_fre) return -EOPNOTSUPP; The kernel then freely emulates any requested mode when there is no FPU but sticks to only true hardware modes when there is an FPU. = More detailed discussion = There has been debate internally at IMG over the issue of FPU emulation so I think it is appropriate to comment on why emulation is not always desirable according to the new o32 FP ABI extensions. I'll try to be brief... The simple reason is that it is obviously better to use a true hardware FPU mode whenever possible. Most of the o32 hard-float ABI variants can execute in multiple hardware modes and the glibc dynamic linker will probe to find the best supported hardware mode by trying them: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/mips/dl-machine-reject-phdr.h;h=b277450c4d02088acb8f24c74cea6ce04783688f;hb=0bd956720c457ff054325b48f26ac7c91cb060e8#l286 If an FPU exists but an emulated mode is used rather than a true hardware mode then the code will run slower than necessary. The second aspect to avoiding emulated modes is that users may have multiple versions of an object available each with different ABI extensions. If one fails to load then the next one may succeed with a true hardware-supported mode. With all that in mind I suspect we can find a balance (in a later update) that may be able to balance the desire for emulation against the desire for using real hardware modes. As it stands there is no clear-cut answer or spec for this so I am in agreement with the overall behaviour of this patch, perhaps with the tweak applied. thanks, Matthew
