[PATCH 1/2] char: hide sparse expensive pointer subtraction warning in specialix.c

[PATCH 1/2] char: hide sparse expensive pointer subtraction warning in specialix.c

[Harvey Harrison]

The warnings come from two static inlines so the ugliness in hiding them
is well contained.
drivers/char/specialix.c:238:19: warning: potentially expensive pointer subtraction
drivers/char/specialix.c:245:19: warning: potentially expensive pointer subtraction

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
---
Andrew, take it or leave it, I just did this to make it easier to look at the other
sparse issues....but without this sparse produces > 100 of these warnings for this
file.

 drivers/char/specialix.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/specialix.c b/drivers/char/specialix.c
index c0e08c7..5487f37 100644
--- a/drivers/char/specialix.c
+++ b/drivers/char/specialix.c
@@ -228,21 +228,21 @@ static inline int sx_paranoia_check(struct specialix_port const * port,
 /* Get board number from pointer */
 static inline int board_No (struct specialix_board * bp)
 {
-	return bp - sx_board;
+	return ((char *)bp - (char *)sx_board) * sizeof(*bp);
 }
 

 /* Get port number from pointer */
 static inline int port_No (struct specialix_port const * port)
 {
-	return SX_PORT(port - sx_port);
+	return SX_PORT(((char *)port - (char *)sx_port) * sizeof(*port));
 }
 

 /* Get pointer to board from pointer to port */
 static inline struct specialix_board * port_Board(struct specialix_port const * port)
 {
-	return &sx_board[SX_BOARD(port - sx_port)];
+	return &sx_board[SX_BOARD(port_No(port))];
 }
 

-- 
1.5.4.2.200.g99e75

[PATCH 1/2] char: hide sparse expensive pointer subtraction warning in specialix.c

[Harvey Harrison]

The warnings come from two static inlines so the ugliness in hiding them
is well contained.
drivers/char/specialix.c:238:19: warning: potentially expensive pointer subtraction
drivers/char/specialix.c:245:19: warning: potentially expensive pointer subtraction

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
---
Bernd noticed that I'm an idiot.  I was only hiding them to see what else
was in the file.  This patch is at least functionally correct.

Brown-paper-bagged-by: Harvey Harrison

 drivers/char/specialix.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/specialix.c b/drivers/char/specialix.c
index c0e08c7..34c7de6 100644
--- a/drivers/char/specialix.c
+++ b/drivers/char/specialix.c
@@ -228,21 +228,21 @@ static inline int sx_paranoia_check(struct specialix_port const * port,
 /* Get board number from pointer */
 static inline int board_No (struct specialix_board * bp)
 {
-	return bp - sx_board;
+	return ((char *)bp - (char *)sx_board) / sizeof(*bp);
 }
 
 
 /* Get port number from pointer */
 static inline int port_No (struct specialix_port const * port)
 {
-	return SX_PORT(port - sx_port);
+	return SX_PORT(((char *)port - (char *)sx_port) / sizeof(*port));
 }
 
 
 /* Get pointer to board from pointer to port */
 static inline struct specialix_board * port_Board(struct specialix_port const * port)
 {
-	return &sx_board[SX_BOARD(port - sx_port)];
+	return &sx_board[SX_BOARD(port_No(port))];
 }
 
 
-- 
1.5.4.2.200.g99e75

Re: [PATCH 1/2] char: hide sparse expensive pointer subtraction warning in specialix.c

[Joe Perches]

On Fri, 2008-02-22 at 10:34 -0800, Harvey Harrison wrote:
> Andrew, take it or leave it, I just did this to make it easier to look at the other
> sparse issues....but without this sparse produces > 100 of these warnings for this
> file.
> 
>  drivers/char/specialix.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/specialix.c b/drivers/char/specialix.c
> index c0e08c7..5487f37 100644
> --- a/drivers/char/specialix.c
> +++ b/drivers/char/specialix.c
> @@ -228,21 +228,21 @@ static inline int sx_paranoia_check(struct specialix_port const * port,
>  /* Get board number from pointer */
>  static inline int board_No (struct specialix_board * bp)
>  {
> -	return bp - sx_board;
> +	return ((char *)bp - (char *)sx_board) * sizeof(*bp);
>  }

You've casted addresses to char then multiplied.
You need to divide.

Maybe it'd be better to change your sparse settings to
not print this warning rather than change normally
readable code to avoid the warning.

I like the control name "ptr-subtraction-blows".

$ make C=1 CHECKFLAGS="-Wno-ptr-subtraction-blows" drivers/char/specialix.o
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  CALL    scripts/checksyscalls.sh
  CHECK   drivers/char/specialix.c
drivers/char/specialix.c:2112:3: warning: context imbalance in 'sx_throttle' - unexpected unlock
  CC      drivers/char/specialix.o
drivers/char/specialix.c:2488: warning: ‘specialx_pci_tbl’ defined but not used