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Re: New 'PL_lc_numeric_mutex' warnings when building with clang

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From:
James E Keenan
Date:
February 26, 2018 01:14
Subject:
Re: New 'PL_lc_numeric_mutex' warnings when building with clang
Message ID:
14c128b9-ba2e-5ea0-f16d-934ef9f4b474@pobox.com
On 02/25/2018 12:13 PM, Karl Williamson wrote:
> On 02/25/2018 08:12 AM, James E Keenan wrote:
>> When building perl as I typically do on FreeBSD-11.0 (clang, 
>> threaded), I have begun to experience a large number of 'make' 
>> warnings not previously seen.  Gzipped build log attached, but here is 
>> a taste:
> 
> I had seen these and researched them, but in order to meet the deadline, 
> I committed anyway, as they are harmless.  I'm sorry that I didn't 
> communicate this issue, so that you spent time on it.  We need to find a 
> way to silence these warnings, and I presume that there is.  I looked 
> them up, and in some documentation about it somewhere, it admits that 
> this is bogus; that their analysis routine that's generating these 
> doesn't get this situation right.
> 
>>
>> #####
>> dump.c:497:9: warning: mutex 'PL_lc_numeric_mutex' is not held on 
>> every path through here [-Wthread-safety-analysis]
>>          STORE_LC_NUMERIC_SET_STANDARD();
>>          ^
>> ./perl.h:5950:13: note: expanded from macro 
>> 'STORE_LC_NUMERIC_SET_STANDARD'
>>              LC_NUMERIC_LOCK(_NOT_IN_NUMERIC_STANDARD);     \
>>              ^
>> ./perl.h:5593:9: note: expanded from macro 'LC_NUMERIC_LOCK'
>>          STMT_START {     \
>>          ^
>> ./perl.h:530:29: note: expanded from macro 'STMT_START'
>> #   define STMT_START   (void)( /* gcc supports "({ STATEMENTS; })" */
>>                                ^
>> dump.c:497:9: note: mutex acquired here
>> ./perl.h:5950:13: note: expanded from macro 
>> 'STORE_LC_NUMERIC_SET_STANDARD'
>>              LC_NUMERIC_LOCK(_NOT_IN_NUMERIC_STANDARD);     \
>>              ^
>> ./perl.h:5595:17: note: expanded from macro 'LC_NUMERIC_LOCK'
>>                  MUTEX_LOCK(&PL_lc_numeric_mutex);     \
>>                  ^
>> ./thread.h:216:14: note: expanded from macro 'MUTEX_LOCK'
>>          if ((_eC_ = 
>> perl_pthread_mutex_lock((m))))                      \
>>                      ^
>> ./thread.h:206:40: note: expanded from macro 'perl_pthread_mutex_lock'
>> #    define perl_pthread_mutex_lock(m) perl_tsa_mutex_lock(m)
>>                                         ^
>> dump.c:499:9: warning: releasing mutex 'PL_lc_numeric_mutex' that was 
>> not held [-Wthread-safety-analysis]
>>          RESTORE_LC_NUMERIC();
>>          ^
>> ./perl.h:5923:13: note: expanded from macro 'RESTORE_LC_NUMERIC'
>>              LC_NUMERIC_UNLOCK;     \
>>              ^
>> ./perl.h:5617:17: note: expanded from macro 'LC_NUMERIC_UNLOCK'
>>                  MUTEX_UNLOCK(&PL_lc_numeric_mutex);     \
>>                  ^
>> ./thread.h:224:14: note: expanded from macro 'MUTEX_UNLOCK'
>>          if ((_eC_ = 
>> perl_pthread_mutex_unlock((m))))                    \
>>                      ^
>> ./thread.h:207:42: note: expanded from macro 'perl_pthread_mutex_unlock'
>> #    define perl_pthread_mutex_unlock(m) perl_tsa_mutex_unlock(m)
>>                                           ^
>> #####
>>
>> The first smoke test where I logged these warnings was at this commit:
>>
>> #####
>> $ gitshowf 2a05854a1ad5472d00de22f8fcc284cdc8fd1503
>> commit 2a05854a1ad5472d00de22f8fcc284cdc8fd1503
>> Merge: 6de18f4 957ac25
>> Author:     Father Chrysostomos <sprout@cpan.org>
>> AuthorDate: Sun Feb 18 16:41:09 2018 -0800
>> Commit:     Father Chrysostomos <sprout@cpan.org>
>> CommitDate: Sun Feb 18 16:41:09 2018 -0800
>>
>>      [Merge] ‘Nonelem’ scalars
>>
>> #####
>>
>> However, based on 'git blame perl.h', I suspect that the warnings were 
>> first introduced here:
>>
>> #####
>> commit 49d7d366441813aa7301b1a437e302372f04f31a
>> Author:     Karl Williamson <khw@cpan.org>
>> AuthorDate: Tue Feb 13 13:12:50 2018 -0700
>> Commit:     Karl Williamson <khw@cpan.org>
>> CommitDate: Sun Feb 18 15:44:23 2018 -0700
>>
>>      Latch LC_NUMERIC during critical sections
>> #####
>>
>> Karl, can you take a look?
>>
>> Thank you very much.
>> Jim Keenan

One thing I find curious/annoying is that I do not get these warnings 
when I build with clang (and threaded) on Linux or FreeBSD-10.3 -- only 
on FreeBSD-11.0.

Carlos Guevara:  Are you getting warnings like these in your FreeBSD-12 
smokers?

Thank you very much.
Jim Keenan

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