Messages in this thread | | | Subject | Re: [PATCH V8 1/2] printk: remove tabular output for NULL pointer | From | Joe Perches <> | Date | Thu, 26 Oct 2017 07:47:19 -0700 |
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On Thu, 2017-10-26 at 20:37 +1100, Tobin C. Harding wrote: > 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.
The idea for aligning is described in commit 5e0579812834a
$ git log --stat -p -1 --format=email 5e0579812834a From 5e0579812834ab7fa072db4a15ebdff68d62e2e7 Mon Sep 17 00:00:00 2001 From: Joe Perches <joe@perches.com> Date: Tue, 26 Oct 2010 14:22:50 -0700 Subject: [PATCH] vsprintf.c: use default pointer field size for "(null)" strings
It might be nicer to align the output.
For instance, ACPI messages sometimes have "(null)" pointers.
$ dmesg | grep "(null)" -A 1 -B 1 [ 0.198733] ACPI: Dynamic OEM Table Load: [ 0.198745] ACPI: SSDT (null) 00239 (v02 PmRef Cpu0Ist 00003000 INTL 20051117) [ 0.199294] ACPI: SSDT 7f596e10 001C7 (v02 PmRef Cpu0Cst 00003001 INTL 20051117) [ 0.200708] ACPI: Dynamic OEM Table Load: [ 0.200721] ACPI: SSDT (null) 001C7 (v02 PmRef Cpu0Cst 00003001 INTL 20051117) [ 0.201950] ACPI: SSDT 7f597f10 000D0 (v02 PmRef Cpu1Ist 00003000 INTL 20051117) [ 0.203386] ACPI: Dynamic OEM Table Load: [ 0.203398] ACPI: SSDT (null) 000D0 (v02 PmRef Cpu1Ist 00003000 INTL 20051117) [ 0.203871] ACPI: SSDT 7f595f10 00083 (v02 PmRef Cpu1Cst 00003000 INTL 20051117) [ 0.205301] ACPI: Dynamic OEM Table Load: [ 0.205315] ACPI: SSDT (null) 00083 (v02 PmRef Cpu1Cst 00003000 INTL 20051117)
> > 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()
Because passing NULL to any of the %p<foo> extensions excluding %pK is probably a defect.
> > > > > 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.
I wonder about this and userland programs and API breakage.
I'd expect there could be cases of userland parsers that expect a certain width for pointer fields.
$ git grep -E "\bseq_.*%p\W" | wc -l 112
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