id = 1878
title = "QEMU doesn't implement ARMv4/v5 legacy SCTLR.U==0 load-and-rotate unaligned access handling"
state = "opened"
created_at = "2023-09-11T14:22:36.971Z"
closed_at = "n/a"
labels = ["target: arm"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/1878"
host-os = "Windows 11 Pro 22H2"
host-arch = "x64"
qemu-version = "8.0.94 (v8.1.0-rc4-12032-g74a4cbee04)"
guest-os = "bare metal software"
guest-arch = "ARM"
description = """**ldr r7, \\[r0, r1\\]** works differently on real device and QEMU. Probably all **ldr Rd, \\[Rs\\]** commands works wrongly in QEMU with Raspberry Pi emulation."""
reproduce = """1. Launch the attached software **kernel_qemu.img** in QEMU.
2. Launch the attached software **kerenel.img** on real Raspberry Pi 1B+.
3. Look at the r7. It contains different data."""
additional = """**kernel_qemu.img** and **kerenel.img** are the same program. It just compiled with different origins - 0x8000 for real device and 0x10000 for QEMU. But code inside the program works at the same addresses.

r0 = 0x183a4

r1 = 0x817

**\\[r0, r1\\]** points to byte 0x42 in memory with such data:

**0x80 0x15 0x22 \\[0x42\\] 0x03 0x21 0x87**

After **ldr r7, \\[r0, r1\\]** execution real device puts to r7: **0x22158042**

After **ldr r7, \\[r0, r1\\]** execution QEMU puts to r7: **0x87210342**

QEMU:

![QEMU.png](/uploads/51ecbf1689d36f969cb482f2613ccb58/QEMU.png)

Real Raspberry Pi 1B+: ![real.jpg](/uploads/2a9cc3f4bc33d7f254c549e5086070a7/real.jpg)

[kernel_qemu.img](/uploads/ae6a7490660569d5fe56adc9f4dde85d/kernel_qemu.img) [kernel.img](/uploads/48c94a66370c1fe8720fe89603c45c7b/kernel.img)"""