On 11/6/24 00:29, Philippe Mathieu-Daudé wrote:
We assumed most guest vCPUs run with the same endianness of the binary. Now we want to swap wrt the vCPU, not the binary. So indeed this patch effectively undo the memory.c swapping (feature). I suppose the better way is to modify memory.c, possibly passing MemOp all over. For HW accel where vCPU endianness is forced to host one, this would become a no-op. Lot of rework in perspective.
It should be much easier than that. First of all, this is when memory.c swaps according to DEVICE_*_ENDIAN: guest \ host little-endian big-endian little-endian BIG LITTLE, NATIVE big-endian BIG, NATIVE LITTLE tswap swaps in the two cases marked "NATIVE" (same as DEVICE_NATIVE_ENDIAN). ldl_le_p swaps in the two cases marked "LITTLE" (same as DEVICE_LITTLE_ENDIAN). ldl_be_p swaps in the two cases marked "BIG" (same as DEVICE_BIG_ENDIAN). First of all, current code does different things for RAM vs. the other registers. After your patch it's the same, which seems fishy. Anyway let's focus on RAM for now. Current code (unconditional tswap + DEVICE_NATIVE_ENDIAN) always performs an even number of swaps: guest \ host little-endian big-endian little-endian none tswap+memory.c big-endian tswap+memory.c none That's what Edgar says - it's just RAM. So with your patch the behavior becomes: guest \ host little-endian big-endian little-endian bswap+memory.c bswap big-endian memory.c none Behavior changes in the cross-endianness case. LE-on-LE remains the same. It seems to break BE hosts since petalogix is a qemu-system-microblazeel board. If this reasoning is correct, together with DEVICE_BIG_ENDIAN you need cpu_to_be32 instead of tswap: guest \ host little-endian big-endian little-endian cpu_to_be32+memory.c none big-endian cpu_to_be32+memory.c none
However, things are different for the R_RX* and R_TX* cases. Before: guest \ host little-endian big-endian little-endian none memory.c big-endian memory.c none Your patch here keeps the same evenness of swaps, even if who swaps changes: guest \ host little-endian big-endian little-endian bswap+memory.c bswap big-endian memory.c none Is this just a change in migration format for the RAM ara? Then I guess your patch works, though I'd prefer Richard's suggestion of flipping the endianness in the MemoryRegionOps. However, since you said the board is LE-only, maybe the following also works and seems simpler? 1) use DEVICE_LITTLE_ENDIAN (i.e. always the same perspective as qemu-microblazeel) 2) use cpu_to_le32 for RAM and nothing for the other registers But again, maybe I'm completely wrong. Paolo
