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 issuesbut 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
  CALLscripts/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


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[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 <[EMAIL PROTECTED]>
---
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 _board[SX_BOARD(port - sx_port)];
+   return _board[SX_BOARD(port_No(port))];
 }
 
 
-- 
1.5.4.2.200.g99e75


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[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 <[EMAIL PROTECTED]>
---
Andrew, take it or leave it, I just did this to make it easier to look at the 
other
sparse issuesbut 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 _board[SX_BOARD(port - sx_port)];
+   return _board[SX_BOARD(port_No(port))];
 }
 

-- 
1.5.4.2.200.g99e75


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[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 [EMAIL PROTECTED]
---
Andrew, take it or leave it, I just did this to make it easier to look at the 
other
sparse issuesbut 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


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[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 [EMAIL PROTECTED]
---
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


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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 issuesbut 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
  CALLscripts/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


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the body of a message to [EMAIL PROTECTED]
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Please read the FAQ at  http://www.tux.org/lkml/