Re: [PATCH v5 17/31] target/arm: Enforce alignment for LDM/STM

[Richard Henderson]

On 8/31/21 2:51 AM, Nathan Chancellor wrote:
> I just bisected a boot hang with an LLVM-built multi_v7_defconfig +
> CONFIG_THUMB2_KERNEL=y kernel down to this commit. I do not see the same
> hang when the kernel is compiled with GCC 11.2.0 and binutils 2.37 nor
> do I see a hang with multi_v7_defconfig by itself. Is there something
> that LLVM is doing wrong when compiling/assembling/linking the kernel or
> is there something wrong/too aggressive with this commit? I can
> reproduce this with current QEMU HEAD (ad22d05833).
>
> My QEMU invocation is:
>
> $ qemu-system-arm \
>      -append "console=ttyAMA0 earlycon" \
>      -display none \
>      -initrd rootfs.cpio \
>      -kernel zImage \
>      -M virt \
>      -m 512m \
>      -nodefaults \
>      -no-reboot \
>      -serial mon:stdio
>
> and the rootfs.cpio and zImage files can be found here:
>
> https://github.com/nathanchance/bug-files/tree/15c1fd6e44622a3c27823d2c5c3083dfc7246146/qemu-2e1f39e29bf9a6b28eaee9fc0949aab50dbad94a

Hmm.  I see

IN:
0xc13038e2:  e890 008c  ldm.w    r0, {r2, r3, r7}

R00=c13077ca R01=c11a8058 R02=c11a8058 R03=c031737f
R04=48379000 R05=00000024 R06=c031748d R07=c03174bb
R08=412fc0f1 R09=c0ce9308 R10=50c5387d R11=00000000
R12=00000009 R13=c1501f88 R14=c0301739 R15=c13038e2
PSR=200001f3 --C- T svc32
Taking exception 4 [Data Abort]
...from EL1 to EL1
...with ESR 0x25/0x9600003f
...with DFSR 0x1 DFAR 0xc13077ca

So, yes, it's a ldm from an address % 4 = 2, so it is correct that we should trap.  You 
should see the same trap on real hw.


r~