From: Niels de Vos <hidden> Date: 2011-05-10 09:21:20
When DBG() is used in a simple if-else, the resulting code path
currently depends on the definition of DBG(). Inserting the statement in
a "do { ... } while (0)" prevents this possible misuse.
Signed-off-by: Niels de Vos <redacted>
---
Note, I have not found any offenders, but a mistake can easily be made.
The following example shows what can go wrong if little intention is
paid to the definition of the DBG() macro.
Example:
if something_went_wrong()
DBG("oh no, something went wrong!\n");
else
printk("all went fine\n");
Old result where the else is placed inside the first if-statment:
if something_went_wrong() {
if (omapfb_debug) {
printk(KERN_DEBUG "oh no, something went wrong!\n");
} else {
printk("all went fine\n");
}
}
New result where the else is an alternative to the first if-statement:
if something_went_wrong() {
do {
if (omapfb_debug)
printk(KERN_DEBUG "oh no, something went wrong!\n");
} while (0);
} else {
printk("all went fine\n");
}
---
drivers/video/omap2/omapfb/omapfb.h | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
-----Original Message-----
From: linux-omap-owner@vger.kernel.org
[mailto:linux-omap-owner@vger.kernel.org] On Behalf Of Niels de Vos
Sent: Tuesday, May 10, 2011 2:51 PM
To: linux-omap@vger.kernel.org
Cc: linux-fbdev@vger.kernel.org;
linux-kernel@vger.kernel.org; Niels de Vos
Subject: [PATCH] omap2/omapfb: make DBG() more resistant in
if-else constructions
When DBG() is used in a simple if-else, the resulting code path
currently depends on the definition of DBG(). Inserting the
statement in
a "do { ... } while (0)" prevents this possible misuse.
Signed-off-by: Niels de Vos <redacted>
---
Note, I have not found any offenders, but a mistake can
easily be made.
The following example shows what can go wrong if little intention is
paid to the definition of the DBG() macro.
Example:
if something_went_wrong()
DBG("oh no, something went wrong!\n");
else
printk("all went fine\n");
Old result where the else is placed inside the first if-statment:
if something_went_wrong() {
if (omapfb_debug) {
printk(KERN_DEBUG "oh no, something
went wrong!\n");
} else {
printk("all went fine\n");
}
}
New result where the else is an alternative to the first if-statement:
if something_went_wrong() {
do {
if (omapfb_debug)
printk(KERN_DEBUG "oh no,
something went wrong!\n");
} while (0);
} else {
printk("all went fine\n");
}
---
drivers/video/omap2/omapfb/omapfb.h | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/video/omap2/omapfb/omapfb.h
b/drivers/video/omap2/omapfb/omapfb.h
index 1305fc9..a01b0bb 100644
A real good find. Wondering if it really didn't create any problems so far...
~sanjeev
#else
#define DBG(format, ...)
#endif
--
1.7.4.4
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On Tue, May 10, 2011 at 11:20, Niels de Vos [off-list ref] wrote:
When DBG() is used in a simple if-else, the resulting code path
currently depends on the definition of DBG(). Inserting the statement in
a "do { ... } while (0)" prevents this possible misuse.
Signed-off-by: Niels de Vos <redacted>
#ifdef DEBUG
extern unsigned int omapfb_debug;
#define DBG(format, ...) \
- if (omapfb_debug) \
- printk(KERN_DEBUG "OMAPFB: " format, ## __VA_ARGS__)
+ do { \
+ if (omapfb_debug) \
+ printk(KERN_DEBUG "OMAPFB: " format, ## __VA_ARGS__); \
+ while (0)
Where's the closing '}'?
#else
#define DBG(format, ...)
BTW, no printf()-style format checking here.
#endif
What about using the standard pr_debug()/dev_dbg() instead?
With dynamic debug, it can be enabled at run time.
As a bonus, you get printf()-style format checking if debugging is disabled.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
From: Niels de Vos <hidden> Date: 2011-05-10 10:57:23
On Tue, May 10, 2011 at 10:42 AM, Geert Uytterhoeven
[off-list ref] wrote:
On Tue, May 10, 2011 at 11:20, Niels de Vos [off-list ref] wrote:
quoted
When DBG() is used in a simple if-else, the resulting code path
currently depends on the definition of DBG(). Inserting the statement in
a "do { ... } while (0)" prevents this possible misuse.
Signed-off-by: Niels de Vos <redacted>
#ifdef DEBUG
extern unsigned int omapfb_debug;
#define DBG(format, ...) \
- if (omapfb_debug) \
- printk(KERN_DEBUG "OMAPFB: " format, ## __VA_ARGS__)
+ do { \
+ if (omapfb_debug) \
+ printk(KERN_DEBUG "OMAPFB: " format, ## __VA_ARGS__); \
+ while (0)
Where's the closing '}'?
Good catch! That's in a "fixup!" that I forgot to squash :-/
I'll post an update version in a bit.
quoted
#else
#define DBG(format, ...)
BTW, no printf()-style format checking here.
quoted
#endif
What about using the standard pr_debug()/dev_dbg() instead?
With dynamic debug, it can be enabled at run time.
As a bonus, you get printf()-style format checking if debugging is disabled.
I think removing DBG() and the omapfb_debug module-parameter is surely
a good thing. Unfortunately DBG() is used quite a bit in the code and
replacing them 'll take some more time. I don't know yet when I find
some time to do and test that.
Thanks for the pointers,
Niels
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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From: Niels de Vos <hidden> Date: 2011-05-10 11:09:49
When DBG() is used in a simple if-else, the resulting code path
currently depends on the definition of DBG(). Inserting the statement in
a "do { ... } while (0)" prevents this possible misuse.
Signed-off-by: Niels de Vos <redacted>
---
V2: add the missing closing }
Note, I have not found any offenders, but a mistake can easily be made.
The following example shows what can go wrong if little intention is
paid to the definition of the DBG() macro.
Example:
if something_went_wrong()
DBG("oh no, something went wrong!\n");
else
printk("all went fine\n");
Old result where the else is placed inside the first if-statment:
if something_went_wrong() {
if (omapfb_debug) {
printk(KERN_DEBUG "oh no, something went wrong!\n");
} else {
printk("all went fine\n");
}
}
New result where the else is an alternative to the first if-statement:
if something_went_wrong() {
do {
if (omapfb_debug)
printk(KERN_DEBUG "oh no, something went wrong!\n");
} while (0);
} else {
printk("all went fine\n");
}
---
drivers/video/omap2/omapfb/omapfb.h | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
From: Tomi Valkeinen <hidden> Date: 2011-05-10 12:08:12
On Tue, 2011-05-10 at 11:42 +0200, Geert Uytterhoeven wrote:
What about using the standard pr_debug()/dev_dbg() instead?
With dynamic debug, it can be enabled at run time.
As a bonus, you get printf()-style format checking if debugging is disabled.
Yes, dev_dbg & co. would be better.
However, one thing I dislike about them is the extra stuff they print.
For example, for omapfb and omapdss dev_dbg will print:
omapfb omapfb: foo
omapdss_dss omapdss_dss: foo
I originally added the debug macros to omapdss to be able to
automatically print the DSS module name, as at that point there was only
one big omapdss device. And I guess I just followed with similar macro
in omapfb also. But I believe both omapdss and omapfb should be changed
to dev_* prints sometime soon.
Tomi
On Tue, May 10, 2011 at 14:08, Tomi Valkeinen [off-list ref] wrote:
On Tue, 2011-05-10 at 11:42 +0200, Geert Uytterhoeven wrote:
quoted
What about using the standard pr_debug()/dev_dbg() instead?
With dynamic debug, it can be enabled at run time.
As a bonus, you get printf()-style format checking if debugging is disabled.
Yes, dev_dbg & co. would be better.
However, one thing I dislike about them is the extra stuff they print.
For example, for omapfb and omapdss dev_dbg will print:
omapfb omapfb: foo
omapdss_dss omapdss_dss: foo
I originally added the debug macros to omapdss to be able to
automatically print the DSS module name, as at that point there was only
one big omapdss device. And I guess I just followed with similar macro
in omapfb also. But I believe both omapdss and omapfb should be changed
to dev_* prints sometime soon.
If you don't want the extra baggage, do
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
and use pr_debug().
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
From: Tomi Valkeinen <hidden> Date: 2011-05-10 12:16:15
On Tue, 2011-05-10 at 12:07 +0100, Niels de Vos wrote:
When DBG() is used in a simple if-else, the resulting code path
currently depends on the definition of DBG(). Inserting the statement in
a "do { ... } while (0)" prevents this possible misuse.
Signed-off-by: Niels de Vos <redacted>