pr_debug

[Alexander Kapshuk]

On Wed, Mar 15, 2017 at 11:15 PM, Tobin C. Harding <me at tobin.cc> wrote:
> On Wed, Mar 15, 2017 at 12:12:48PM +0100, Bjørn Mork wrote:
>> Alexander Kapshuk <alexander.kapshuk at gmail.com> writes:
>>
>> >>> On Wed, Mar 15, 2017 at 10:31 AM, Tobin C. Harding <me at tobin.cc> wrote:
>> >>> > why does calling pr_debug() with more than one argument cause a sparse
>> >>> > warning?
>> >>> >
>> >>> > drivers/mmc/core/sdio_io.c:70:9: error: unknown field name in initializer
>> >>> >
>> >>> > sdio_io.c:70:
>> >>> > pr_debug("SDIO: Enabling device %s...\n", sdio_func_id(func));
>> ..
>> > 'sdio_func_id()' is a macro defined here:
>> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/include/linux/mmc/sdio_func.h?id=refs/tags/v4.11-rc2
>> > #define sdio_func_id(f) (dev_name(&(f)->dev))
>>
>>
>> So the "func" in that debug call contains a 'struct device'.  Any
>> reason why the pr_debug() shouldn't be converted to something like
>>
>>  dev_dbg(&func->dev, "SDIO: Enabling device...\n");
>
> Good point Bjørn, thanks. And thank you Alexander for your input. I
> fear I may have sent you both on a wild goose chase with the example
> that I chose. pr_debug() causes a sparse warning in many instances
> when the format string includes format specifiers.
>
> /* this is fine */
> pr_debug("some info string");
>
> /* this often causes Sparse warning */
> pr_debug("string with specifier: %d", foo);
>
> A simple example can be seen by adding this function
>
> void foo(const char *baz)
> {
>         pr_debug("cause Sparse warning - %s\n", baz);
> }
>
> To a random driver, and running `make C=2 M=drivers/staging/ks7010`
>
> drivers/staging/ks7010/ks_hostif.c:2702:9: error: unknown field name in initializer
>
> For more examples from the kernel tree, running:
> $ make -j9 C=2 M=drivers/staging 2>sparse.out
>
> gives many such cases, for example:
>
> drivers/staging/fbtft/fbtft-core.c:472:17: error: unknown field name in initialize
> drivers/staging/media/bcm2048/radio-bcm2048.c:2596:17: error: unknown field name in initializer
> drivers/staging/dgnc/dgnc_tty.c:1274:17: error: unknown field name in initializer
>
> Also dev_debug causes the same sparse warning at times, for example:
>
> drivers/staging/comedi/comedi_fops.c:352:17: error: unknown field name in initialize
>
>         if (s->busy) {
>                 dev_dbg(dev->class_dev,
>                         "subdevice is busy, cannot resize buffer\n");
>                 return -EBUSY;
>         }
>
> And 2 more example instances of dev_debug:
> drivers/staging/comedi/drivers/das16.c:578:25: error: unknown field name in initialize
> drivers/staging/dgnc/dgnc_tty.c:1274:17: error: unknown field name in initializer
>
> thanks,
> Tobin.

The pr_debug() manpage, https://www.kernel.org/doc/local/pr_debug.txt,
states that:

Some files call pr_debug(), which is ordinarily an empty macro that discards
    its arguments at compile time.  To enable debugging output, build the
    appropriate file with -DDEBUG by adding

      CFLAGS_[filename].o := -DDEBUG

    to the makefile.

You did not mention whether you have compiling those modules with the
DEBUG flag enabled, so, perhaps if you didn't, that could be the
reason why you've been getting those errors.