On 6/30/23 14:25, Anton Johansson via wrote:
CPUNegativeOffsetState is a struct placed immediately before CPUArchState in the ArchCPU struct. Its purpose is to ensure that certain fields (CPUTLBDescFast, IcountDecr) lay within a small negative offset of CPUArchState in memory. This is desired for better code-generation on arm[32|64] and riscv hosts which has addressing modes with 12- and 11 bits of displacement respectively.
The purpose is also to ensure that general purpose registers stay close to the beginning of the CPUArchState and thus can also be accessed with a small displacement.
Can you check if this becomes worse for any architecture? On some 64-bit targets, 8 bytes * 32 registers is 512 bytes and it's a substantial part of the 11 bits that are available.
Paolo
