So basically using them should be safe as long as you're in EfiGetCurrentTpl() < TPL_HIGH_LEVEL, right? 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. 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
