Re: [PATCH] ACPI: PRM: Clean Up guid type in struct prm_handler_info

[Rafael J. Wysocki]

On Thu, Oct 24, 2024 at 12:40 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Thu, 24 Oct 2024 at 10:07, Dan Carpenter <dan.carpenter@xxxxxxxxxx> 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@xxxxxxxxxx>
> > Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>
> In case this wasn't implied already,
>
> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

Applied, thanks!

> > ---
> > 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;
> > --