[PATCH] acpica: fix -Wnull-pointer-arithmetic warnings

[PATCH] acpica: fix -Wnull-pointer-arithmetic warnings

[Qian Cai]

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. Fix it by doing an integer arithmetic
instead.

Signed-off-by: Qian Cai <cai@lca.pw>
---
 include/acpi/actypes.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
index ad6892a24015..25b4a32da177 100644
--- a/include/acpi/actypes.h
+++ b/include/acpi/actypes.h
@@ -500,13 +500,13 @@ typedef u64 acpi_integer;
 
 #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) (p))
 #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) (acpi_uintptr_t) (p))
-#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
+#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) + (acpi_size)(b))
 #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b)))
 #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8, (a)) - ACPI_CAST_PTR (u8, (b))))
 
 /* Pointer/Integer type conversions */
 
-#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0, (acpi_size) (i))
+#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0, (acpi_size) (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)

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

[Nick Desaulniers]

On Tue, Jul 16, 2019 at 8:38 PM Qian Cai <cai@lca.pw> wrote:
>
> 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. Fix it by doing an integer arithmetic
> instead.

Hi Qian, thanks for the patch.  How do I reproduce this issue,
precisely?  I just tried:
$ make CC=clang -j71 drivers/acpi/scan.o
on linux-next today and don't observe the warning.  My clang is ToT
built sometime this week.  It looks like drivers/acpi/scan.o when
CONFIG_ACPI=y, which is set in the defconfig.  Is there another set of
configs to enable to observe the warning?

Also, the fix is curious.  Arithmetic on pointers to different
"objects" (with one element passed the end) may lead to provence
issues due to undefined behavior, but I would have expected some cases
to uintptr_t, then arithmetic on that type, as the solution (which is
what I suspect ACPI_CAST_PTR is doing).

Further, you seem to have modified ACPI_ADD_PTR but not ACPI_SUB_PTR;
I would have expected both to be afflicted together or not at all
based on their existing implementations.

>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  include/acpi/actypes.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
> index ad6892a24015..25b4a32da177 100644
> --- a/include/acpi/actypes.h
> +++ b/include/acpi/actypes.h
> @@ -500,13 +500,13 @@ typedef u64 acpi_integer;
>
>  #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) (p))
>  #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) (acpi_uintptr_t) (p))
> -#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
> +#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) + (acpi_size)(b))
>  #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b)))
>  #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8, (a)) - ACPI_CAST_PTR (u8, (b))))
>
>  /* Pointer/Integer type conversions */
>
> -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0, (acpi_size) (i))
> +#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0, (acpi_size) (i))

IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ?
-- 
Thanks,
~Nick Desaulniers

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

[Qian Cai]

> On Jul 17, 2019, at 6:01 PM, Nick Desaulniers <ndesaulniers@google.com> wrote:
> 
> On Tue, Jul 16, 2019 at 8:38 PM Qian Cai <cai@lca.pw> wrote:
>> 
>> 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. Fix it by doing an integer arithmetic
>> instead.
> 
> Hi Qian, thanks for the patch.  How do I reproduce this issue,
> precisely?  I just tried:
> $ make CC=clang -j71 drivers/acpi/scan.o
> on linux-next today and don't observe the warning.  My clang is ToT
> built sometime this week.  It looks like drivers/acpi/scan.o when
> CONFIG_ACPI=y, which is set in the defconfig.  Is there another set of
> configs to enable to observe the warning?

# make W=1 -j 256

With the config,

https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config 

> 
> Also, the fix is curious.  Arithmetic on pointers to different
> "objects" (with one element passed the end) may lead to provence
> issues due to undefined behavior, but I would have expected some cases
> to uintptr_t, then arithmetic on that type, as the solution (which is
> what I suspect ACPI_CAST_PTR is doing).
> 
> Further, you seem to have modified ACPI_ADD_PTR but not ACPI_SUB_PTR;
> I would have expected both to be afflicted together or not at all
> based on their existing implementations.

Yes, I thought about that, but ACPI_SUB_PTR does not seem used anywhere, so I thought maybe just start a new discussion to remove it all together later.


> 
>> 
>> Signed-off-by: Qian Cai <cai@lca.pw>
>> ---
>> include/acpi/actypes.h | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
>> index ad6892a24015..25b4a32da177 100644
>> --- a/include/acpi/actypes.h
>> +++ b/include/acpi/actypes.h
>> @@ -500,13 +500,13 @@ typedef u64 acpi_integer;
>> 
>> #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) (p))
>> #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) (acpi_uintptr_t) (p))
>> -#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
>> +#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) + (acpi_size)(b))
>> #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b)))
>> #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8, (a)) - ACPI_CAST_PTR (u8, (b))))
>> 
>> /* Pointer/Integer type conversions */
>> 
>> -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0, (acpi_size) (i))
>> +#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0, (acpi_size) (i))
> 
> IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ?
> -- 
> Thanks,
> ~Nick Desaulniers

RE: [PATCH] acpica: fix -Wnull-pointer-arithmetic warnings

[Moore, Robert]

-----Original Message-----
From: Qian Cai [mailto:cai@lca.pw] 
Sent: Wednesday, July 17, 2019 5:50 PM
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Wysocki, Rafael J <rafael.j.wysocki@intel.com>; Moore, Robert <robert.moore@intel.com>; Schmauss, Erik <erik.schmauss@intel.com>; jkim@freebsd.org; Len Brown <lenb@kernel.org>; linux-acpi@vger.kernel.org; devel@acpica.org; clang-built-linux <clang-built-linux@googlegroups.com>; LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] acpica: fix -Wnull-pointer-arithmetic warnings



> On Jul 17, 2019, at 6:01 PM, Nick Desaulniers <ndesaulniers@google.com> wrote:
> 
> On Tue, Jul 16, 2019 at 8:38 PM Qian Cai <cai@lca.pw> wrote:
>> 
>> 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. Fix it by doing an integer arithmetic 
>> instead.
> 
> Hi Qian, thanks for the patch.  How do I reproduce this issue, 
> precisely?  I just tried:
> $ make CC=clang -j71 drivers/acpi/scan.o on linux-next today and don't 
> observe the warning.  My clang is ToT built sometime this week.  It 
> looks like drivers/acpi/scan.o when CONFIG_ACPI=y, which is set in the 
> defconfig.  Is there another set of configs to enable to observe the 
> warning?

# make W=1 -j 256

With the config,

https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config 

> 
> Also, the fix is curious.  Arithmetic on pointers to different 
> "objects" (with one element passed the end) may lead to provence 
> issues due to undefined behavior, but I would have expected some cases 
> to uintptr_t, then arithmetic on that type, as the solution (which is 
> what I suspect ACPI_CAST_PTR is doing).
> 
> Further, you seem to have modified ACPI_ADD_PTR but not ACPI_SUB_PTR; 
> I would have expected both to be afflicted together or not at all 
> based on their existing implementations.

Yes, I thought about that, but ACPI_SUB_PTR does not seem used anywhere, so I thought maybe just start a new discussion to remove it all together later.

ACPI_SUB_PTR is used in the iasl data table compiler.


> 
>> 
>> Signed-off-by: Qian Cai <cai@lca.pw>
>> ---
>> include/acpi/actypes.h | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index 
>> ad6892a24015..25b4a32da177 100644
>> --- a/include/acpi/actypes.h
>> +++ b/include/acpi/actypes.h
>> @@ -500,13 +500,13 @@ typedef u64 acpi_integer;
>> 
>> #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) (p))
>> #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) (acpi_uintptr_t) (p))
>> -#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
>> +#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) + (acpi_size)(b))

We have some questions concerning this change. If (a) is not cast to a u8, the addition will be in whatever units are appropriate for (a) i.e., the type of (a). However, we want ACPI_ADD_PTR (And ACPI_SUB_PTR) to simply perform a byte addition or subtraction - thus the cast to u8. I believe that is the original thinking behind the macros.

>> #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b)))
>> #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8, (a)) - ACPI_CAST_PTR (u8, (b))))
>> 
>> /* Pointer/Integer type conversions */
>> 
>> -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0, (acpi_size) (i))
>> +#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0, (acpi_size) (i))
> 
> IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ?
> --
> Thanks,
> ~Nick Desaulniers

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

[Qian Cai]

On Tue, 2019-07-23 at 20:49 +0000, Moore, Robert wrote:
> > > Signed-off-by: Qian Cai <cai@lca.pw>
> > > ---
> > > include/acpi/actypes.h | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index 
> > > ad6892a24015..25b4a32da177 100644
> > > --- a/include/acpi/actypes.h
> > > +++ b/include/acpi/actypes.h
> > > @@ -500,13 +500,13 @@ typedef u64 acpi_integer;
> > > 
> > > #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) (p))
> > > #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) (acpi_uintptr_t) (p))
> > > -#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR
> > > (u8, (a)) + (acpi_size)(b)))
> > > +#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) +
> > > (acpi_size)(b))
> 
> We have some questions concerning this change. If (a) is not cast to a u8, the
> addition will be in whatever units are appropriate for (a) i.e., the type of
> (a). However, we want ACPI_ADD_PTR (And ACPI_SUB_PTR) to simply perform a byte
> addition or subtraction - thus the cast to u8. I believe that is the original
> thinking behind the macros.

I posted a v2 a while ago, and should clear this concern.

> 
> > > #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR
> > > (u8, (a)) - (acpi_size)(b)))
> > > #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8,
> > > (a)) - ACPI_CAST_PTR (u8, (b))))
> > > 
> > > /* Pointer/Integer type conversions */
> > > 
> > > -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void *) 0,
> > > (acpi_size) (i))
> > > +#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0,
> > > (acpi_size) (i))
> > 
> > IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ?
> > --
> > Thanks,
> > ~Nick Desaulniers
> 
> 

RE: [PATCH] acpica: fix -Wnull-pointer-arithmetic warnings

[Moore, Robert]

-----Original Message-----
From: Qian Cai [mailto:cai@lca.pw] 
Sent: Wednesday, July 24, 2019 6:40 AM
To: Moore, Robert <robert.moore@intel.com>; Nick Desaulniers <ndesaulniers@google.com>
Cc: Wysocki, Rafael J <rafael.j.wysocki@intel.com>; Schmauss, Erik <erik.schmauss@intel.com>; jkim@freebsd.org; Len Brown <lenb@kernel.org>; linux-acpi@vger.kernel.org; devel@acpica.org; clang-built-linux <clang-built-linux@googlegroups.com>; LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] acpica: fix -Wnull-pointer-arithmetic warnings

On Tue, 2019-07-23 at 20:49 +0000, Moore, Robert wrote:
> > > Signed-off-by: Qian Cai <cai@lca.pw>
> > > ---
> > > include/acpi/actypes.h | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index
> > > ad6892a24015..25b4a32da177 100644
> > > --- a/include/acpi/actypes.h
> > > +++ b/include/acpi/actypes.h
> > > @@ -500,13 +500,13 @@ typedef u64 acpi_integer;
> > > 
> > > #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) 
> > > (p)) #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) 
> > > (acpi_uintptr_t) (p)) -#define ACPI_ADD_PTR(t, a, b)           
> > > ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
> > > +#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) +
> > > (acpi_size)(b))
> 
> We have some questions concerning this change. If (a) is not cast to a 
> u8, the addition will be in whatever units are appropriate for (a) 
> i.e., the type of (a). However, we want ACPI_ADD_PTR (And 
> ACPI_SUB_PTR) to simply perform a byte addition or subtraction - thus 
> the cast to u8. I believe that is the original thinking behind the macros.

I posted a v2 a while ago, and should clear this concern.

OK then this change only affects ACPI_TO_POINTER?

+#define ACPI_TO_POINTER(i)              ACPI_CAST_PTR (void, i)


> 
> > > #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, 
> > > (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b))) #define 
> > > ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8,
> > > (a)) - ACPI_CAST_PTR (u8, (b))))
> > > 
> > > /* Pointer/Integer type conversions */
> > > 
> > > -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void 
> > > *) 0,
> > > (acpi_size) (i))
> > > +#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0,
> > > (acpi_size) (i))
> > 
> > IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ?
> > --
> > Thanks,
> > ~Nick Desaulniers
> 
> 

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

[Qian Cai]

On Wed, 2019-07-24 at 14:17 +0000, Moore, Robert wrote:
> 
> -----Original Message-----
> From: Qian Cai [mailto:cai@lca.pw] 
> Sent: Wednesday, July 24, 2019 6:40 AM
> To: Moore, Robert <robert.moore@intel.com>; Nick Desaulniers <ndesaulniers@goo
> gle.com>
> Cc: Wysocki, Rafael J <rafael.j.wysocki@intel.com>; Schmauss, Erik <erik.schma
> uss@intel.com>; jkim@freebsd.org; Len Brown <lenb@kernel.org>; linux-acpi@vger
> .kernel.org; devel@acpica.org; clang-built-linux <clang-built-linux@googlegrou
> ps.com>; LKML <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH] acpica: fix -Wnull-pointer-arithmetic warnings
> 
> On Tue, 2019-07-23 at 20:49 +0000, Moore, Robert wrote:
> > > > Signed-off-by: Qian Cai <cai@lca.pw>
> > > > ---
> > > > include/acpi/actypes.h | 4 ++--
> > > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index
> > > > ad6892a24015..25b4a32da177 100644
> > > > --- a/include/acpi/actypes.h
> > > > +++ b/include/acpi/actypes.h
> > > > @@ -500,13 +500,13 @@ typedef u64 acpi_integer;
> > > > 
> > > > #define ACPI_CAST_PTR(t, p)             ((t *) (acpi_uintptr_t) 
> > > > (p)) #define ACPI_CAST_INDIRECT_PTR(t, p)    ((t **) 
> > > > (acpi_uintptr_t) (p)) -#define ACPI_ADD_PTR(t, a, b)           
> > > > ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) + (acpi_size)(b)))
> > > > +#define ACPI_ADD_PTR(t, a, b)           ACPI_CAST_PTR (t, (a) +
> > > > (acpi_size)(b))
> > 
> > We have some questions concerning this change. If (a) is not cast to a 
> > u8, the addition will be in whatever units are appropriate for (a) 
> > i.e., the type of (a). However, we want ACPI_ADD_PTR (And 
> > ACPI_SUB_PTR) to simply perform a byte addition or subtraction - thus 
> > the cast to u8. I believe that is the original thinking behind the macros.
> 
> I posted a v2 a while ago, and should clear this concern.
> 
> OK then this change only affects ACPI_TO_POINTER?
> 
> +#define ACPI_TO_POINTER(i)              ACPI_CAST_PTR (void, i)

Yes.

> 
> 
> > 
> > > > #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, 
> > > > (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b))) #define 
> > > > ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8,
> > > > (a)) - ACPI_CAST_PTR (u8, (b))))
> > > > 
> > > > /* Pointer/Integer type conversions */
> > > > 
> > > > -#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, (void 
> > > > *) 0,
> > > > (acpi_size) (i))
> > > > +#define ACPI_TO_POINTER(i)              ACPI_ADD_PTR (void, 0,
> > > > (acpi_size) (i))
> > > 
> > > IIUC, these are adding `i` to NULL (or (void*)0)? X + 0 == X ?
> > > --
> > > Thanks,
> > > ~Nick Desaulniers
> > 
> >