Re: [PATCH v11] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests

From: Guenter Roeck <linux@roeck-us.net>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Russell King <linux@armlinux.org.uk>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	David Laight <David.Laight@aculab.com>,
	Charlie Jenkins <charlie@rivosinc.com>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	Helge Deller <deller@gmx.de>,
	Palmer Dabbelt <palmer@rivosinc.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Parisc List <linux-parisc@vger.kernel.org>
Subject: Re: [PATCH v11] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests
Date: Sun, 3 Mar 2024 07:26:55 -0800	[thread overview]
Message-ID: <6df98c91-26b1-497a-9202-18bf86c0130d@roeck-us.net> (raw)
In-Reply-To: <f422742a-4c86-4cb0-a4f7-a62f0310eb23@csgroup.eu>

On 3/3/24 02:20, Christophe Leroy wrote:
> 
> 
> Le 01/03/2024 à 19:32, Guenter Roeck a écrit :
>> This leaves the mps2-an385:mps2_defconfig crash, which is avoided by
>> this patch.
>> My understanding, which may be wrong, is that arm images with thumb
>> instructions
>> do not support unaligned accesses (maybe I should say do not support
>> unaligned
>> accesses with the mps2-an385 qemu emulation; I did not test with real
>> hardware,
>> after all).
>>
>> Given all that, the continued discussion around the subject, and the lack
>> of agreement if unaligned accesses should be tested or not, I don't really
>> see a path forward for this patch. The remaining known problem is arm with
>> thumb instructions. I don't think that is going to be fixed. I suspect that
>> no one but me even tries to run that code (or any arm:nommu images, for
>> that
>> matter). I'd suggest to drop this patch, and I'll stop testing IP checksum
>> generation for mps2-an385:mps2_defconfig.
> 
> I'm trying to run an ARM kernel built with GCC 13.2 and mps2_defconfig
> on the mps2-an385 qemu emulation, and I get the following fatal error.
> 
> $ qemu-system-arm -M mps2-an385 -kernel vmlinux
> qemu: fatal: Lockup: can't escalate 3 to HardFault (current priority -1)
> 
> R00=00000000 R01=00000000 R02=00000000 R03=00000000
> R04=00000000 R05=00000000 R06=00000000 R07=00000000
> R08=00000000 R09=00000000 R10=00000000 R11=00000000
> R12=00000000 R13=ffffffe0 R14=fffffff9 R15=00000000
> XPSR=40000003 -Z-- A handler
> FPSCR: 00000000
> Abandon (core dumped)
> 
> Can you tell how to proceed ?
> 

You can't run it directly. mps2-an385 is one of the platforms where
the qemu maintainers insisted that qemu shall not initialize the CPU.
You have to provide a shim such as
https://github.com/groeck/linux-build-test/blob/master/rootfs/arm/mps2-boot.axf
as bios. You also have to provide the dtb file.

On top of that, you would need a customized version of qemu which
actually reads the command line, the bios file, and the dtb. See
https://github.com/groeck/linux-build-test/tree/master/qemu
branch v8.2.1-local or v8.1.5-local.

It might be possible to find a bootloader which does all that and
prepares the emulation for running Linux, but I don't know if that
exists somewhere.

Guenter