ARM to C calling convention, NEON registers to save

Question

There is a similar post that covers regular registers. What about NEON registers. As far as I remember either top half or bottom half of registers have to be preserved across function calls. I can't find that info anywhere, can somebody clarify that?

thanks

From the AAPCS, §5.1.1 Core registers:

• r0-r3 are the argument and scratch registers; r0-r1 are also the result registers
• r4-r8 are callee-save registers
• r9 might be a callee-save register or not (on some variants of AAPCS it is a special register)
• r10-r11 are callee-save registers
• r12-r15 are special registers

From the AAPCS, §5.1.2.1 VFP register usage conventions (VFP v2, v3 and the Advanced SIMD Extension):

• s16–s31 (d8–d15, q4–q7) must be preserved
• s0–s15 (d0–d7, q0–q3) and d16–d31 (q8–q15) do not need to be preserved

Answer 1

From the AAPCS, §5.1.2.1:

• s16–s31 (d8–d15, q4–q7) must be preserved
• s0–s15 (d0–d7, q0–q3) and d16–d31 (q8–q15) do not need to be preserved