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
