[PATCH] docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]

[PATCH] docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]

[Joe Perches]

Standard integer promotion is already done and %hx and %hhx is useless
so do not encourage the use of %hh[xudi] or %h[xudi].

As Linus said in:
Link: https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/

It's a pointless warning, making for more complex code, and
making people remember esoteric printf format details that have no
reason for existing.

The "h" and "hh" things should never be used. The only reason for them
being used if if you have an "int", but you want to print it out as a
"char" (and honestly, that is a really bad reason, you'd be better off
just using a proper cast to make the code more obvious).

So if what you have a "char" (or unsigned char) you should always just
print it out as an "int", knowing that the compiler already did the
proper type conversion.

Signed-off-by: Joe Perches <joe@perches.com>
---
 Documentation/core-api/printk-formats.rst | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index c6224d039bcb..ecbebf4ca8e7 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -13,10 +13,10 @@ Integer types
 
 	If variable is of Type,		use printk format specifier:
 	------------------------------------------------------------
-		char			%hhd or %hhx
-		unsigned char		%hhu or %hhx
-		short int		%hd or %hx
-		unsigned short int	%hu or %hx
+		char			%d or %x
+		unsigned char		%u or %x
+		short int		%d or %x
+		unsigned short int	%u or %x
 		int			%d or %x
 		unsigned int		%u or %x
 		long			%ld or %lx
@@ -25,10 +25,10 @@ Integer types
 		unsigned long long	%llu or %llx
 		size_t			%zu or %zx
 		ssize_t			%zd or %zx
-		s8			%hhd or %hhx
-		u8			%hhu or %hhx
-		s16			%hd or %hx
-		u16			%hu or %hx
+		s8			%d or %x
+		u8			%u or %x
+		s16			%d or %x
+		u16			%u or %x
 		s32			%d or %x
 		u32			%u or %x
 		s64			%lld or %llx

Re: [PATCH] docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]

[Louis Taylor]

On Fri, Sep 06, 2019 at 02:11:51PM -0700, Joe Perches wrote:
> Standard integer promotion is already done and %hx and %hhx is useless
> so do not encourage the use of %hh[xudi] or %h[xudi].
> 
> As Linus said in:
> Link: https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/
> 
> It's a pointless warning, making for more complex code, and
> making people remember esoteric printf format details that have no
> reason for existing.
> 
> The "h" and "hh" things should never be used. The only reason for them
> being used if if you have an "int", but you want to print it out as a
> "char" (and honestly, that is a really bad reason, you'd be better off
> just using a proper cast to make the code more obvious).
> 
> So if what you have a "char" (or unsigned char) you should always just
> print it out as an "int", knowing that the compiler already did the
> proper type conversion.

Yeah, makes sense. Sorry for adding these in the first place.

Reviewed-by: Louis Taylor <louis@kragniz.eu>

Re: [PATCH] docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]

[Andy Shevchenko]

On Sat, Sep 7, 2019 at 9:15 PM Joe Perches <joe@perches.com> wrote:
>
> Standard integer promotion is already done and %hx and %hhx is useless
> so do not encourage the use of %hh[xudi] or %h[xudi].
>
> As Linus said in:
> Link: https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/
>
> It's a pointless warning, making for more complex code, and
> making people remember esoteric printf format details that have no
> reason for existing.
>
> The "h" and "hh" things should never be used. The only reason for them
> being used if if you have an "int", but you want to print it out as a
> "char" (and honestly, that is a really bad reason, you'd be better off
> just using a proper cast to make the code more obvious).
>
> So if what you have a "char" (or unsigned char) you should always just
> print it out as an "int", knowing that the compiler already did the
> proper type conversion.

> -               char                    %hhd or %hhx
> -               short int               %hd or %hx
> +               char                    %d or %x
> +               short int               %d or %x

> +               s8                      %d or %x
> +               s16                     %d or %x

This is incorrect. Integral promotions promotes also sign, which will
produce too many f:s.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]

[Jani Nikula]

On Fri, 06 Sep 2019, Joe Perches <joe@perches.com> wrote:
> Link: https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/

I thought Link: was for referencing the patch on the mailing list that
became the commit in git.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center

Re: [PATCH] docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]

[Jonathan Corbet]

On Fri, 06 Sep 2019 14:11:51 -0700
Joe Perches <joe@perches.com> wrote:

> Standard integer promotion is already done and %hx and %hhx is useless
> so do not encourage the use of %hh[xudi] or %h[xudi].
> 
> As Linus said in:
> Link: https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/
> 
> It's a pointless warning, making for more complex code, and
> making people remember esoteric printf format details that have no
> reason for existing.
> 
> The "h" and "hh" things should never be used. The only reason for them
> being used if if you have an "int", but you want to print it out as a
> "char" (and honestly, that is a really bad reason, you'd be better off
> just using a proper cast to make the code more obvious).
> 
> So if what you have a "char" (or unsigned char) you should always just
> print it out as an "int", knowing that the compiler already did the
> proper type conversion.
> 
> Signed-off-by: Joe Perches <joe@perches.com>

Applied, thanks.

I took the liberty of removing "Link:" (but not the URL) from the commit
message.  That wasn't a patch tag, there is no real reason to make it
look like one...

jon