Re: [PATCH] was Re: [PATCH 2/3] [delete] Not-so-harmless spurious call to `wait4`

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

>> From 5c3756e9eb0342b1a5a23bcb54d5b8317743ce0d Mon Sep 17 00:00:00 2001
>> From: Dominique Quatravaux <dominique.quatravaux@epfl.ch <mailto:dominique.quatravaux@epfl.ch>>
>> Date: Thu, 8 Apr 2021 21:35:57 +0200
>> Subject: [PATCH] [delete] not-so-harmless spurious call to `wait4`
>> MIME-Version: 1.0
>> Content-Type: text/plain; charset=UTF-8
>> Content-Transfer-Encoding: 8bit
>>
>> As seen in https://sourceware.org/bugzilla/show_bug.cgi?id=24069 <https://sourceware.org/bugzilla/show_bug.cgi?id=24069> this
>> code will typically wait4() a second time on the same process that was
>> already wait4()'d a few lines above. While this used to be
>> harmless/idempotent (when we assumed that the process already exited),
>> this now causes a deadlock in the WIFSTOPPED case.
>>
>> The early (~2019) history of bug #24069 cautiously suggests to use
>> WNOHANG instead of outright deleting the call. However, tests on the
>> current version of Darwin (Big Sur) demonstrate that gdb runs just
>> fine without a redundant call to wait4(), as would be expected.
>> Notwithstanding the debatable value of conserving bug compatibility
>> with an OS release that is more than a decade old, there is scant
>> evidence of what that double-wait4() was supposed to achieve in the
>> first place
> 
> Thanks, this looks good.  If we had more contributors for macOS,
> especially some that cared about old macOS versions, we could aim at
> supporting many versions back.  But given the current state, it's
> perfectly reasonable to aim at making GDB work well for the latest
> version.
> 
>  - A cursory investigation with `git blame` pinpoints
>> commits bb00b29d7802 and a80b95ba67e2 from the 2008-2009 era, but
>> fails to answer the “why” question conclusively.
> 
> Yes, the commits that predate the usage of git don't have the patch
> message / rationale that people sent along with the patch, it just
> wasn't recorded in CVS.  You can always dig into into the mailing
> list.
> 
> a80b95ba67e2: https://pi.simark.ca/gdb-patches/F1826DD8-CC0F-4FF1-BC47-3F2ACBB42909@adacore.com/
> bb00b29d7802: https://pi.simark.ca/gdb-patches/20090319141746.GA81236@ulanbator.act-europe.fr/
> 
> Although there isn't more details about the bit you are removing.
> 
> So let's just wait until we hear back from the FSF about your copyright
> assignment, and then we can merge all of this.
> 
> Note that we currently require contributions to include ChangeLog
> entries:
> 
>     https://sourceware.org/gdb/wiki/ContributionChecklist#Properly_Formatted_GNU_ChangeLog
> 
> I don't mind for this time, the patches are small enough that I can
> write them when merging.  We are also discussing whether we keep using
> those, so it may or may not apply in the future.
> 
> Simon
> 

Hi Dominique,

Now that your copyright assignment is done, I'd like to merge your
patches, but I'm a bit lost and the patches don't apply because they got
messed up in the process of sending them.  Would you mind sending a
clean v2, rebased on today's master (I don't think it will change much,
darwin-nat.c hasn't had other changes)?  And if you could use
git-send-email, that would make sure the patches arrive correctly
formatted.

Thanks,

Simon