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Re: [PATCH 5/5] check_kernel_printf.c: warn about "%lx", (long)ptr — Semantic Matching Tool

Re: [PATCH 5/5] check_kernel_printf.c: warn about "%lx", (long)ptr

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On 26 October 2017 at 12:48, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> On Wed, Oct 25, 2017 at 09:25:15PM +0200, Rasmus Villemoes wrote:
>> For some reason this spits out an enourmous amount of false positives,
>> making this entirely useless. We hit a lot of "%lx", (long)(a - b),
>> but I don't understand why the a-b expression (a pointer difference)
>> passes is_ptr_type().
> Well, it is a pointer type.  If you do pointer math, you get pointer
> results.  You can't really treat subtract different from addition
> because container_of() is a subtraction.

Huh? When I subtract one pointer from another, I get an _integer_. The
math done in container_of is subtracting an integer from a pointer
which does give a pointer, of course, but that's not the issue here.
The false positives I'm talking about are (at least those I checked)
something like

ptr = array;
<misc logic, incrementing ptr along the way>
if (uhoh)
  printk("trouble with array element %lx\n", (long)(ptr - array));

which is obviously ok.
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