Re: Schrödinger's hash

On 2026-06-22 at 18:40, David Christensen wrote:

> On 6/22/26 09:54, Charles Curley wrote:

>> I think that this problem first showed up late April or early May.
>> If that is correct, the following extracts from my apt logs might
>> help. These were copied and pasted unwrapped, so unless they were
>> mangled in transit, long lines should be preserved.
>> 
>> ...
>> 
>> Apparently, twice in April I had tried the backports kernel(s),
>> and found them unsatisfactory. So possibly the fix came in between 
>> linux-image-6.19.11+deb13-amd64 and the current backports kernel, 
>> linux-image-7.0.10+deb13-amd64.
> 
> AIUI if someone can come up with a shell script or program whose exit
>  value reliably indicates the presence or absence of a bug, Git can
> do a binary search over a range of commits and locate the commit
> where the bug originated.

...assuming that there aren't any commits broken for other reasons, or
otherwise commits where the codebase can't be built far enough for the
script or program to be able to do its thing, that will be hit along the
way.

That could be folded in under "reliably", of course - but it's
sufficiently far out of the scope of what people might be expected to
think of for that term, if not previously familiar with what such
bisections can involve, that it seems worth calling out explicitly.

That said, git can actually do this even *without* such a
script/program, as long as you're willing and able to test each
candidate commit manually. The use of a script or program to automate it
is actually a subset of the functionality of the 'git bisect'
sub-command, specifically the sub-sub-command 'git bisect run'; see 'git
help bisect' for the documentation, most of which is about the version
of the process where the validation of each commit is done manually
rather than by a script.

-- 
   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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