diff --git a/qemu/target/arm/helper.c b/qemu/target/arm/helper.c index e7b3fe7b..10b327a5 100644 --- a/qemu/target/arm/helper.c +++ b/qemu/target/arm/helper.c @@ -5695,16 +5695,24 @@ static void do_v7m_exception_exit(ARMCPU *cpu) env->regs[12] = ldl_phys(cs->as, frameptr + 0x10); env->regs[14] = ldl_phys(cs->as, frameptr + 0x14); env->regs[15] = ldl_phys(cs->as, frameptr + 0x18); + + /* Returning from an exception with a PC with bit 0 set is defined + * behaviour on v8M (bit 0 is ignored), but for v7M it was specified + * to be UNPREDICTABLE. In practice actual v7M hardware seems to ignore + * the lsbit, and there are several RTOSes out there which incorrectly + * assume the r15 in the stack frame should be a Thumb-style "lsbit + * indicates ARM/Thumb" value, so ignore the bit on v7M as well, but + * complain about the badly behaved guest. + */ if (env->regs[15] & 1) { - qemu_log_mask(LOG_GUEST_ERROR, - "M profile return from interrupt with misaligned " - "PC is UNPREDICTABLE\n"); - /* Actual hardware seems to ignore the lsbit, and there are several - * RTOSes out there which incorrectly assume the r15 in the stack - * frame should be a Thumb-style "lsbit indicates ARM/Thumb" value. - */ env->regs[15] &= ~1U; + if (!arm_feature(env, ARM_FEATURE_V8)) { + qemu_log_mask(LOG_GUEST_ERROR, + "M profile return from interrupt with misaligned " + "PC is UNPREDICTABLE on v7M\n"); + } } + xpsr = ldl_phys(cs->as, frameptr + 0x1c); if (arm_feature(env, ARM_FEATURE_V8)) {