Messages in this thread | | | Date | Thu, 26 Oct 2017 20:37:28 +1100 | From | "Tobin C. Harding" <> | Subject | Re: [PATCH V8 1/2] printk: remove tabular output for NULL pointer |
| |
On Thu, Oct 26, 2017 at 01:05:39AM -0700, Joe Perches wrote: > On Thu, 2017-10-26 at 17:27 +1100, Tobin C. Harding wrote: > > Hi Joe, > > > > thanks for your review. > > > > On Wed, Oct 25, 2017 at 09:57:23PM -0700, Joe Perches wrote: > > > On Thu, 2017-10-26 at 13:53 +1100, Tobin C. Harding wrote: > > > > Currently pointer() checks for a NULL pointer argument and then if so > > > > attempts to print "(null)" with _some_ standard width. This width cannot > > > > correctly be ascertained here because many of the printk specifiers > > > > print pointers of varying widths. > > > > > > I believe this is not a good change. > > > Only pointers without a <foo> extension call pointer() > > > > Sorry, I don't understand what you mean here. All the %p<foo> specifier code is > > handled by pointer()? > > Sorry, I was imprecise/wrong. > > None of the %p<foo> extensions except %pK and %p<invalid_foo> > actually use this bit of the pointer() call.
if (!ptr && *fmt != 'K') { /* * Print (null) with the same width as a pointer so it makes * tabular output look nice. */ if (spec.field_width == -1) spec.field_width = default_width; return string(buf, end, "(null)", spec); }
Is there something I'm missing here? This code reads like its all %p<foo> (including %p and %p<invalid_foo>) except %pK that hit this block when a NULL pointer is passed in.
> All of the other valid %p<foo> extension uses do not end up > at this block being executed so it's effectively only regular > pointers being output by number() > > > > > Remove the attempt to print NULL pointers with a correct width. > > > > > > the correct width for a %p is the default width. > > > > It is the default width if we are printing addresses. Once we hash 64 > > bit address to a 32 bit identifier then we don't have a default width. > > Perhaps that 32 bit identifier should use leading 0's for > the default width.
That's a fair comment.
> aside: > > Why hash 64 bits to 32? > Why shouldn't the hash width be 64 bits on 64 bit systems?
Quoted from Linus in an earlier thread discussing this change
Date: Thu, 12 Oct 2017 11:37:22 -0700 Linus Torvalds wrote:
In fact, I'd prefer mapping the pointer to a 32-bit value, even on 64-bit architectures. When people use these things for debugging and for identifying which device node or socket or whatever they are tracking, we're generally talking a (small) handful of different devices or whatever.
Hope this helps, Tobin.
| |