linux-kernel - Re: [PATCH] ACPI: PRM: Clean Up guid type in struct prm_handler

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Message-ID: <CAMj1kXFRUhkCyN0PjLrtw1uSCuy4m=9g=pwNO9tkxckj-koijg@mail.gmail.com>
Date: Thu, 24 Oct 2024 12:39:49 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Koba Ko <kobak@...dia.com>, Len Brown <lenb@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	kernel-janitors@...r.kernel.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] ACPI: PRM: Clean Up guid type in struct prm_handler_info

On Thu, 24 Oct 2024 at 10:07, Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> Clang 19 prints a warning when we pass &th->guid to efi_pa_va_lookup():
>
> drivers/acpi/prmt.c:156:29: error: passing 1-byte aligned argument to
> 4-byte aligned parameter 1 of 'efi_pa_va_lookup' may result in an
> unaligned pointer access [-Werror,-Walign-mismatch]
>   156 |                         (void *)efi_pa_va_lookup(&th->guid, handler_info->handler_address);
>       |                                                  ^
>
> The problem is that efi_pa_va_lookup() takes a efi_guid_t and &th->guid
> is a regular guid_t.  The difference between the two types is the
> alignment.  efi_guid_t is a typedef.
>
>         typedef guid_t efi_guid_t __aligned(__alignof__(u32));
>
> It's possible that this a bug in Clang 19.  Even though the alignment of
> &th->guid is not explicitly specified, it will still end up being aligned
> at 4 or 8 bytes.
>
> Anyway, as Ard points out, it's cleaner to change guid to efi_guid_t type
> and that also makes the warning go away.
>
> Fixes: 088984c8d54c ("ACPI: PRM: Find EFI_MEMORY_RUNTIME block for PRM handler and context")
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> Tested-by: Paul E. McKenney <paulmck@...nel.org>

In case this wasn't implied already,

Acked-by: Ard Biesheuvel <ardb@...nel.org>

> ---
> Sorry for the unfair Fixes tags since you obviously aren't to blame.  But it's
> more practical if we avoid breaking the build in backports or etc.  Fixes tags
> are quite often unfair in this way...
>
>  drivers/acpi/prmt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/prmt.c b/drivers/acpi/prmt.c
> index d59307a76ca3..747f83f7114d 100644
> --- a/drivers/acpi/prmt.c
> +++ b/drivers/acpi/prmt.c
> @@ -52,7 +52,7 @@ struct prm_context_buffer {
>  static LIST_HEAD(prm_module_list);
>
>  struct prm_handler_info {
> -       guid_t guid;
> +       efi_guid_t guid;
>         efi_status_t (__efiapi *handler_addr)(u64, void *);
>         u64 static_data_buffer_addr;
>         u64 acpi_param_buffer_addr;
> --
> 2.45.2
>