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Bug 856112 - dev-perl/Math-Pari-2.10.809.0-r2 fails to compile (lto): paricast.h:22:50: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Summary: dev-perl/Math-Pari-2.10.809.0-r2 fails to compile (lto): paricast.h:22:50: er...
Status: CONFIRMED
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: Current packages (show other bugs)
Hardware: All Linux
: Normal normal
Assignee: Gentoo Perl team
URL:
Whiteboard:
Keywords:
Depends on:
Blocks: lto
  Show dependency tree
 
Reported: 2022-07-03 07:39 UTC by Agostino Sarubbo
Modified: 2024-05-02 05:24 UTC (History)
1 user (show)

See Also:
Package list:
Runtime testing required: ---


Attachments
build.log (build.log,70.09 KB, text/plain)
2022-07-03 07:39 UTC, Agostino Sarubbo
Details

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Description Agostino Sarubbo gentoo-dev 2022-07-03 07:39:51 UTC
https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: dev-perl/Math-Pari-2.10.809.0-r2 fails to compile (lto).
Discovered on: amd64 (internal ref: lto_tinderbox)

NOTE:
This machine uses lto with CFLAGS=-flto -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing
Comment 1 Agostino Sarubbo gentoo-dev 2022-07-03 07:39:53 UTC
Created attachment 789869 [details]
build.log

build log and emerge --info
Comment 2 Agostino Sarubbo gentoo-dev 2022-07-03 07:39:55 UTC
Error(s) that match a know pattern in addition to what has been reported in the summary:


sh: line 1: gp: command not found
../../pari-2.3.5/src/headers/paricast.h:22:50: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstrict-aliasing]]
Comment 3 Agostino Sarubbo gentoo-dev 2022-07-26 09:01:08 UTC
Here is a bit of explanation:

-Werror=lto-type-mismatch:
User to find possible runtime issues in packages. It likely means the package is unsafe to build & use with LTO.
For projects using the same identifier but with different types across different files, they must be fixed to be consistent across the codebase.

-Werror=odr:
Used to find possible runtime issues in packages. These bugs are a problem anyway but may be even worse when combined with LTO. C++ code must comply with the One Definition Rule (ODR) - see https://en.cppreference.com/w/cpp/language/definition#One_Definition_Rule.

-Werror=strict-aliasing:
Used to find possible runtime issues in packages. These bugs are a problem anyway but may be even worse when combined with LTO.

Workarounds:
- If upstream is friendly and still active, file a bug upstream. For emulators, codecs, games, or multimedia packages, it may be worth just applying a workaround instead, as upstreams sometimes aren't receptive to these bugs (VALID FOR ALL).
- Use the new 'filter-lto' from flag-o-matic.eclass as it's likely to be unsafe with LTO (VALID FOR lto-type-mismatch - odr).
- Fix it yourself if interested, of course (VALID FOR ALL).
- Append-flags -fno-strict-aliasing (VALID FOR strict-aliasing).
- Use memcpy() but a union is sometimes suitable too (VALID FOR strict-aliasing).
- -fstrict-aliasing is implied by -O2, so this must be addressed in some form (VALID FOR strict-aliasing).

See also: https://marc.info/?l=gentoo-dev&m=165639574126280&w=2
Comment 4 Eli Schwartz gentoo-dev 2024-03-11 00:47:53 UTC
x86_64-pc-linux-gnu-gcc -c -I ../pari-2.3.5/src -I ../pari-2.3.5/src/headers -I ../pari-2.3.5/src -I ./libPARI  -I ../../pari-2.3.5/src -I ../../pari-2.3.5/src/headers -I ../../pari-2.3.5/src/graph -I . -D_REENTRANT -D_GNU_SOURCE -O2 -pipe -march=x86-64 -frecord-gcc-switches -fno-diagnostics-color -fmessage-length=0 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -fwrapv -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -pipe -march=x86-64 -frecord-gcc-switches -fno-diagnostics-color -fmessage-length=0 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing   -DVERSION=\"\" -DXS_VERSION=\"\" -fPIC -Derr=pari_err -DHAS_STAT -DHAS_OPENDIR -DASMINLINE -DGCC_INLINE -DDYNAMIC_PLOTTING -o arith1.o ../../pari-2.3.5/src/basemath/arith1.c
In file included from ../../pari-2.3.5/src/headers/pari.h:69,
                 from ../../pari-2.3.5/src/basemath/arith1.c:22:
../../pari-2.3.5/src/basemath/arith1.c: In function ‘classno’:
../../pari-2.3.5/src/headers/paricast.h:22:50: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstrict-aliasing]]
   22 | #define gmael1(m,x1)             (((GEN*)    (m))[x1])
      |                                                  ^
../../pari-2.3.5/src/headers/paricast.h:28:15: note: in expansion of macro ‘gmael1’
   28 | #define gel   gmael1
      |               ^~~~~~
../../pari-2.3.5/src/basemath/arith1.c:2920:11: note: in expansion of macro ‘gel’
 2920 |           gel(forms,0) = f;
      |           ^~~
Comment 5 Eli Schwartz gentoo-dev 2024-03-11 00:54:38 UTC
So this is very confusing to me, because if I build the same version, I get this:

x86_64-pc-linux-gnu-gcc -c -I ../pari-2.3.5/src -I ../pari-2.3.5/src/headers -I ../pari-2.3.5/src -I ./libPARI  -I ../../pari-2.3.5/src -I ../../pari-2.3.5/src/headers -I ../../pari-2.3.5/src/graph -I . -O2 -pipe -march=x86-64-v3 -fno-strict-aliasing -DNO_PERL_RAND_SEED -fwrapv -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -pipe -march=x86-64-v3 -fno-strict-aliasing   -DVERSION=\"\" -DXS_VERSION=\"\" -fPIC -Derr=pari_err -DHAS_STAT -DHAS_OPENDIR -DASMINLINE -DGCC_INLINE -DDYNAMIC_PLOTTING -o arith1.o ../../pari-2.3.5/src/basemath/arith1.c

It *looks* like maybe this only respects whichever flags perl itself was built with, which makes it hard to know how to resolve this bug... I guess the answer is basically that due to bug 877659 the entire perl world handily opts out of strict-aliasing?