> No, the other way around. You should raise the TPL to TPL_HIGH_LEVEL > to prevent being interrupted by something that may corrupt the NEON > registers. But isn't that only necessary if you assume that interrupt-handlers use VFP registers? afaik on ARM <TPL_HIGH_LEVEL events are never called from the timer interrupt handler so basically if you're going to be interrupted during VFP operations no other <TPL_HIGH_LEVEL code should ever run.
Please correct me if I'm misunderstanding something. On Sun, May 13, 2018 at 12:16 PM Ard Biesheuvel <[email protected]> wrote: > On 13 May 2018 at 11:48, Michael Zimmermann <[email protected]> wrote: > > So basically using them should be safe as long as you're in > > EfiGetCurrentTpl() < TPL_HIGH_LEVEL, right? > No, the other way around. You should raise the TPL to TPL_HIGH_LEVEL > to prevent being interrupted by something that may corrupt the NEON > registers. > > Also, it'd probably be trivial to add VFP/NEON regs to > > EFI_SYSTEM_CONTEXT_ARM though that wouldn't help when writing apps for > > existing uefi platforms. > EFI_SYSTEM_CONTEXT_ARM is covered by the UEFI spec, so that is not > going to change. > > On Sun, May 13, 2018 at 9:32 AM Ard Biesheuvel < [email protected]> > > wrote: > > > >> On 12 May 2018 at 23:11, Michael Zimmermann <[email protected]> > > wrote: > >> > For AArch32 the spec says in 2.3.5.3: > >> >> Floating point, SIMD, vector operations and other instruction set > >> > extensions must not > >> > be used. > >> > > >> > For AArch64 the spec says in 2.3.6.4: > >> >> Floating point and SIMD instructions may be used. > >> > > >> > So is there a reason why AArch32 is not allowed to use Floating point > >> > operations? > >> > I'd understand if this restriction was limited to runtime services only > > but > >> > I don't see how it makes sense for boot services. > >> > > >> > I've written a patch which adds NEON support to FrameBufferBltLib to > >> > increase the rendering performance(by a lot actually) for 24bit displays > >> > and thought about sending it to the mailing list - that's why the > > question > >> > came up. > >> > > > > >> The reason for the difference between AArch64 and the other EFI > >> architectures is that AArch64 does not have a softfloat ABI, so it is > >> impossible to compile floating point code [portably] without enabling > >> VFP/NEON. This is why AArch64 is the exception here. > > > >> Currently, the AArch32 CPU context structure [EFI_SYSTEM_CONTEXT_ARM] > >> does not cover VFP/NEON registers, and so they are not > >> preserved/restored when an interrupt is taken. This means you cannot > >> use VFP/NEON registers in an event handler or you will corrupt the > >> VFP/NEON state of the interrupted context. _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
