Re: [PATCH] target/arm: Don't enforce alignment faults on Device memory for SCTLR.U == 0

On 8/19/26 12:00, Peter Maydell wrote:
> We enforce that we take alignment faults for unaligned accesses
> when the MMU is disabled or the access is to Device memory. This
> is correct for the new-style unaligned accesses rules that were
> introduced in ARMv6 when SCTLR.U == 1 and then became the only
> option from ARMv7 (where SCTLR.U is RES1). However, it isn't
> right for the old ARMv4 and ARMv5 setup (and ARMv6 when SCTLR.U = 0).
> 
> We don't emulate the v4/v5 alignment rules (which notably include
> "for unaligned LDR, do an aligned load and rotate"); but taking an
> alignment fault is definitely wrong and isn't what QEMU has
> traditionally done.  Restrict this behaviour to when SCTLR.U is 1.
> 
> (The other place we enable alignment checks on Device memory is in
> ptw.c, but we only set TLB_CHECK_ALIGNED for LPAE translations, which
> are guaranteed to be v7 or later.)
> 
> Signed-off-by: Peter Maydell<[email protected]>
> ---
>   target/arm/tcg/hflags.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)

Reviewed-by: Richard Henderson <[email protected]>

r~