linux-kernel - Re: [PATCH V2] LoongArch: Align ACPI structures if ARCH_STRICT

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Message-ID: <0104bccd-d3a2-4f6b-8838-0acf0563c4b6@roeck-us.net>
Date: Fri, 26 Sep 2025 11:27:08 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Xi Ruoyao <xry111@...111.site>, Huacai Chen <chenhuacai@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
 Huacai Chen <chenhuacai@...ngson.cn>, loongarch@...ts.linux.dev,
 Xuefeng Li <lixuefeng@...ngson.cn>, Guo Ren <guoren@...nel.org>,
 Xuerui Wang <kernel@...0n.name>, Jiaxun Yang <jiaxun.yang@...goat.com>,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 Binbin Zhou <zhoubinbin@...ngson.cn>
Subject: Re: [PATCH V2] LoongArch: Align ACPI structures if ARCH_STRICT_ALIGN
 enabled

On 9/26/25 10:15, Xi Ruoyao wrote:
> On Fri, 2025-09-26 at 07:31 -0700, Guenter Roeck wrote:
>> On Sun, Sep 21, 2025 at 09:07:38AM +0800, Huacai Chen wrote:
>>> Hi, Nathan,
>>>
>>> On Sun, Sep 21, 2025 at 7:48 AM Nathan Chancellor <nathan@...nel.org> wrote:
>>>>
>>>> Hi Huacai,
>>>>
>>>> On Wed, Sep 10, 2025 at 05:10:33PM +0800, Huacai Chen wrote:
>>>>> ARCH_STRICT_ALIGN is used for hardware without UAL, now it only control
>>>>> the -mstrict-align flag. However, ACPI structures are packed by default
>>>>> so will cause unaligned accesses.
>>>>>
>>>>> To avoid this, define ACPI_MISALIGNMENT_NOT_SUPPORTED in asm/acenv.h to
>>>>> align ACPI structures if ARCH_STRICT_ALIGN enabled.
>>>>>
>>>>> Cc: stable@...r.kernel.org
>>>>> Reported-by: Binbin Zhou <zhoubinbin@...ngson.cn>
>>>>> Suggested-by: Xi Ruoyao <xry111@...111.site>
>>>>> Suggested-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>>>>> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
>>>>> ---
>>>>> V2: Modify asm/acenv.h instead of Makefile.
>>>>>
>>>>>   arch/loongarch/include/asm/acenv.h | 7 +++----
>>>>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/arch/loongarch/include/asm/acenv.h b/arch/loongarch/include/asm/acenv.h
>>>>> index 52f298f7293b..483c955f2ae5 100644
>>>>> --- a/arch/loongarch/include/asm/acenv.h
>>>>> +++ b/arch/loongarch/include/asm/acenv.h
>>>>> @@ -10,9 +10,8 @@
>>>>>   #ifndef _ASM_LOONGARCH_ACENV_H
>>>>>   #define _ASM_LOONGARCH_ACENV_H
>>>>>
>>>>> -/*
>>>>> - * This header is required by ACPI core, but we have nothing to fill in
>>>>> - * right now. Will be updated later when needed.
>>>>> - */
>>>>> +#ifdef CONFIG_ARCH_STRICT_ALIGN
>>>>> +#define ACPI_MISALIGNMENT_NOT_SUPPORTED
>>>>> +#endif /* CONFIG_ARCH_STRICT_ALIGN */
>>>>>
>>>>>   #endif /* _ASM_LOONGARCH_ACENV_H */
>>>>
>>>> I am seeing several ACPI errors in my QEMU testing after this change in
>>>> Linus's tree as commit a9d13433fe17 ("LoongArch: Align ACPI structures
>>>> if ARCH_STRICT_ALIGN enabled").
>>>>
>>>>    $ make -skj"$(nproc)" ARCH=loongarch CROSS_COMPILE=loongarch64-linux- clean defconfig vmlinuz.efi
>>>>    kernel/sched/fair.o: warning: objtool: sched_update_scaling() falls through to next function init_entity_runnable_average()
>>>>    mm/mempolicy.o: warning: objtool: alloc_pages_bulk_mempolicy_noprof+0x380: stack state mismatch: reg1[30]=-1+0 reg2[30]=-2-80
>>>>    lib/crypto/mpi/mpih-div.o: warning: objtool: mpihelp_divrem+0x2d0: stack state mismatch: reg1[22]=-1+0 reg2[22]=-2-16
>>>>    In file included from include/acpi/acpi.h:24,
>>>>                     from drivers/acpi/acpica/tbprint.c:10:
>>>>    drivers/acpi/acpica/tbprint.c: In function 'acpi_tb_print_table_header':
>>>>    include/acpi/actypes.h:530:43: warning: 'strncmp' argument 1 declared attribute 'nonstring' is smaller than the specified bound 8 [-Wstringop-overread]
>>>>      530 | #define ACPI_VALIDATE_RSDP_SIG(a)       (!strncmp (ACPI_CAST_PTR (char, (a)), ACPI_SIG_RSDP, (sizeof(a) < 8) ? ACPI_NAMESEG_SIZE : 8))
>>>>          |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>    drivers/acpi/acpica/tbprint.c:105:20: note: in expansion of macro 'ACPI_VALIDATE_RSDP_SIG'
>>>>      105 |         } else if (ACPI_VALIDATE_RSDP_SIG(ACPI_CAST_PTR(struct acpi_table_rsdp,
>>>>          |                    ^~~~~~~~~~~~~~~~~~~~~~
>>>>    In file included from include/acpi/acpi.h:26:
>>>>    include/acpi/actbl.h:69:14: note: argument 'signature' declared here
>>>>       69 |         char signature[ACPI_NAMESEG_SIZE] ACPI_NONSTRING;       /* ASCII table signature */
>>>>          |              ^~~~~~~~~
>>>>  From this link this seems a comiler issue (at least not an
>>> arch-specific kernel issue):
>>> https://github.com/AOSC-Tracking/linux/commit/1e9ee413357ef58dd902f6ec55013d2a2f2043eb
>>>
>>
>> I see that the patch made it into the upstream kernel, now breaking both
>> mainline and 6.16.y test builds of loongarch64:allmodconfig with gcc.
>>
>> Since this is apparently intentional, I'll stop build testing
>> loongarch64:allmodconfig. So far it looks like my qemu tests
>> are not affected, so I'll continue testing those for the time being.
> 
> See https://gcc.gnu.org/PR122073 and
> https://github.com/acpica/acpica/pull/1050.
> 

I understand that. Every compiler has bugs. Normally workarounds are implemented.
Since that won't happen here, my remedy is to stop testing the affected
configuration(s). I do this whenever I learn that a known problem won't be fixed.
The above is not a complaint, just an information.

Guenter