linux-kernel - Re: [PATCH v2] acpica: fix -Wnull-pointer-arithmetic warnings

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Date:   Thu, 01 Aug 2019 15:16:19 -0400
From:   Qian Cai <cai@....pw>
To:     "Moore, Robert" <robert.moore@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Cc:     "Schmauss, Erik" <erik.schmauss@...el.com>,
        "jkim@...eBSD.org" <jkim@...eBSD.org>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] acpica: fix -Wnull-pointer-arithmetic warnings

On Fri, 2019-07-26 at 19:35 +0000, Moore, Robert wrote:
> We've taken the change to ACPI_TO_POINTER.

I am a bit confused here. I saw the commit in the acpia repo.

https://github.com/acpica/acpica/commit/02bbca5070e42d298c9b824300aa0eb8a082d797

but how does that change will go into the linux kernel? Suppose Rafael will need
to pick it up manually?

> 
> 
> -----Original Message-----
> From: Qian Cai [mailto:cai@....pw] 
> Sent: Thursday, July 18, 2019 12:49 PM
> To: Wysocki, Rafael J <rafael.j.wysocki@...el.com>
> Cc: Moore, Robert <robert.moore@...el.com>; Schmauss, Erik <erik.schmauss@...e
> l.com>; jkim@...eBSD.org; lenb@...nel.org; ndesaulniers@...gle.com; linux-acpi
> @vger.kernel.org; devel@...ica.org; clang-built-linux@...glegroups.com; linux-
> kernel@...r.kernel.org; Qian Cai <cai@....pw>
> Subject: [PATCH v2] acpica: fix -Wnull-pointer-arithmetic warnings
> 
> Clang generate quite a few of those warnings.
> 
> drivers/acpi/scan.c:759:28: warning: arithmetic on a null pointer treated as a
> cast from integer to pointer is a GNU extension [-Wnull-pointer-arithmetic]
> 		status = acpi_get_handle(ACPI_ROOT_OBJECT,
> obj->string.pointer,
>                                          ^~~~~~~~~~~~~~~~
> ./include/acpi/actypes.h:458:56: note: expanded from macro 'ACPI_ROOT_OBJECT'
>  #define ACPI_ROOT_OBJECT                ((acpi_handle) ACPI_TO_POINTER
> (ACPI_MAX_PTR))
> 							^~~~~~~~~~~~~~~
> ./include/acpi/actypes.h:509:41: note: expanded from macro 'ACPI_TO_POINTER'
>  #define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0,
> (acpi_size) (i))
>                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/acpi/actypes.h:503:84: note: expanded from macro 'ACPI_ADD_PTR'
>  #define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t,
> (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
>                                          ^~~~~~~~~~~~~~~~~
> ./include/acpi/actypes.h:501:66: note: expanded from macro 'ACPI_CAST_PTR'
>  #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) (p))
>                                                                  ^ This is
> because pointer arithmetic on a pointer not pointing to an array is an
> undefined behavior (C11 6.5.6, constraint 8). Fix it by just casting the
> corresponding pointers using ACPI_CAST_PTR() and skip the arithmetic. Also,
> fix a checkpatch warning together.
> 
> ERROR: Macros with complex values should be enclosed in parentheses
>  #45: FILE: include/acpi/actypes.h:509:
> +#define ACPI_TO_POINTER(i)              ACPI_CAST_PTR (void, i)
> 
> Signed-off-by: Qian Cai <cai@....pw>
> ---
> 
> v2: Use ACPI_CAST_PTR() in ACPI_TO_POINTER() directly without
>     arithmetic.
> 
>  include/acpi/actypes.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index
> ad6892a24015..163181e2d884 100644
> --- a/include/acpi/actypes.h
> +++ b/include/acpi/actypes.h
> @@ -506,7 +506,7 @@ typedef u64 acpi_integer;
>  
>  /* Pointer/Integer type conversions */
>  
> -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0,
> (acpi_size) (i))
> +#define ACPI_TO_POINTER(i)              (ACPI_CAST_PTR (void, i))
>  #define ACPI_TO_INTEGER(p)              ACPI_PTR_DIFF (p, (void *) 0)
>  #define ACPI_OFFSET(d, f)               ACPI_PTR_DIFF (&(((d *) 0)->f), (void
> *) 0)
>  #define ACPI_PHYSADDR_TO_PTR(i)         ACPI_TO_POINTER(i)
> --
> 2.20.1 (Apple Git-117)
>