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SubjectRe: [PATCH] lib/vsprintf.c: increase the size of the field_width variable
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On Wed, Sep 09 2015, Joe Perches <joe@perches.com> wrote:

> On Wed, 2015-09-09 at 12:13 +0200, Maurizio Lombardi wrote:
>> When printing a bitmap using the "%*pb[l]" printk format
>> a 16 bit variable (field_width) is used to store the size of the bitmap.
>> In some cases 16 bits are not sufficient, the variable overflows and
>> printk does not work as expected.
>
> If more than 16 bits are necessary, it couldn't work
> as a single printk is limited to 1024 bytes.

I'm also a little confused; I don't see what printk has to do with the
reported problem (I'd expect the /sys/... file to be generated by
something like seq_printf).

>> 3. Bitmap should be set, but still empty
>> # cat /sys/bus/pseudo/drivers/scsi_debug/map
> []
>> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> []
>> @@ -384,8 +384,8 @@ struct printf_spec {
>> u8 flags; /* flags to number() */
>> u8 base; /* number base, 8, 10 or 16 only */
>> u8 qualifier; /* number qualifier, one of 'hHlLtzZ' */
>> - s16 field_width; /* width of output field */
>> s16 precision; /* # of digits/chars */
>> + s32 field_width; /* width of output field */
>> };
>>
>> static noinline_for_stack
>
> And this makes the sizeof struct printf_spec more than
> 8 bytes which isn't desireable on x86-32.

Or other architectures, I imagine. I'm pretty sure struct printf_spec
purposely has sizeof==8 to allow it to be (relatively cheaply) passed
around by value.

> %*pb is meant for smallish bitmaps, not big ones.

Yup. And that leads to my other confusion: Given that the expected
output is given as "0-15", does the bitmap really consist of > S16_MAX
bits with only the first 16 set?

Rasmus


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