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+id = 2916
+title = "qemu-system-arm hangs when attempting to enable MMU on Cortex-A7"
+state = "opened"
+created_at = "2025-04-07T11:27:39.291Z"
+closed_at = "n/a"
+labels = ["target: arm", "workflow::Needs Info"]
+url = "https://gitlab.com/qemu-project/qemu/-/issues/2916"
+host-os = "Ubuntu 22.04.5 LTS"
+host-arch = "x86_64"
+qemu-version = "QEMU emulator version 9.2.3"
+guest-os = "bare-metal/?"
+guest-arch = "ARM"
+description = """QEMU 9.x.x+ hangs when attempting to do enable the MMU from SCTLRL - M bit: https://developer.arm.com/documentation/ddi0601/2025-03/AArch32-Registers/SCTLR--System-Control-Register
+
+The instruction that hangs is the writing of the SCTLR register:
+
+```
+mrc     p15, 0, r0, c1, c0, 0
+orr     r0, r0, 1
+mcr     p15, 0, r0, c1, c0, 0
+```
+
+I am attempting to enable unaligned accesses and SCTLR-A bit doesn't seem to have any effect if the SCTLR-M is not enabled. Doing an unaligned access on cortex-a7 should be supported but it always trigger a Fault."""
+reproduce = """1. add the mrc/orr/mcr instruction sequence in the ResetHandler
+2. link the elf
+3. attempt to execute it"""
+additional = """The unaligned access looked like it was working in QEMU 8.x.x but it might not have been emulated(?). I also am facing the same issues with MCR hanging and unaligned access not supported with latest 10.0.0-RC2.
+
+When it hangs, QEMU has to be killed and terminal reset.
+
+There might be two separate issues here:
+
+1. writing SCTLR register
+2. emulated cortex-a7 not supporting unaligned access (hardware supports it)"""