On 13 May 2018 at 11:48, Michael Zimmermann <sigmaepsilo...@gmail.com> 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 <ard.biesheu...@linaro.org> > wrote: > >> On 12 May 2018 at 23:11, Michael Zimmermann <sigmaepsilo...@gmail.com> > 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 edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
