linux-kernel - Re: [PATCH 01/16] dyndbg: drop trim_prefix, obsoleted by __FILE_

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Date:   Fri, 1 Nov 2019 10:20:14 -0600
From:   jim.cromie@...il.com
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Jason Baron <jbaron@...mai.com>,
        LKML <linux-kernel@...r.kernel.org>, Greg KH <greg@...ah.com>,
        clang-built-linux@...glegroups.com,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>, linux-doc@...r.kernel.org
Subject: Re: [PATCH 01/16] dyndbg: drop trim_prefix, obsoleted by __FILE__s
 relative path

Cool, thanks!


On Wed, Oct 30, 2019 at 3:20 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> On 29/10/2019 21.00, Jim Cromie wrote:
> > Regarding:
> > commit 2b6783191da7 ("dynamic_debug: add trim_prefix() to provide source-root relative paths")
> > commit a73619a845d5 ("kbuild: use -fmacro-prefix-map to make __FILE__ a relative path")
> >
> > 2nd commit broke dynamic-debug's "file $fullpath" query form, but
> > nobody noticed because 1st commit trimmed prefixes from control-file
> > output, so the click-copy-pasting of fullpaths into new queries had
> > ceased; that query form became unused.
> >
> > So remove the function and callers; its purpose was to strip the
> > prefix from __FILE__, which is now gone.
>
> I agree with the intent, but I wonder if this is premature. I mean, the
> -fmacro-prefix-map is only for gcc 8+, so this ends up printing the full
> paths when the compiler is just a little old (and the kernel was built
> out-of-tree).
>
> I don't think keeping the current workaround for a year or two more
> should hurt; when int skip = strlen(__FILE__) -
> strlen("lib/dynamic_debug.c"); evaluates to 0 (in-tree build, or build
> with new enough gcc), I'm pretty sure gcc optimizes the rest of the
> function away (it should know that strncmp(x, y, 0) gives 0, and even if
> it didn't, the conditional assigns 0 to skip which it already is, so gcc
> just needs to know that strncmp() is pure).
>
> >
> > Also drop "file $fullpath" from docs, and tweak example to cite column
> > 1 of control-file as valid "file $input".
>
> That part certainly makes sense, since the $fullpath hasn't actually
> been in the control file for a long time.
>
> Rasmus
>


I agree.  Ive split the patch, am keeping the doc change.