Bug 858377 – dev-util/gperf-3.1-r1 fails to compile (lto): keyword-list.icc:50:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]

• Product: Gentoo Linux
• Status: CONFIRMED ---

[Description Agostino Sarubbo 2022-07-16 15:39:34 UTC]

https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: dev-util/gperf-3.1 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 2022-07-16 15:39:36 UTC]

Created attachment 791738 [details]
build.log

build log and emerge --info

[Comment 2 Agostino Sarubbo 2022-07-26 09:01:29 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 3 Agostino Sarubbo 2022-09-26 08:44:00 UTC]

lto_tinderbox has reproduced this issue with version 3.1-r1 - Updating summary.

[Comment 4 Kim B. Sindalsen 2023-01-15 22:55:57 UTC]

Not restricted to LTO - same on non-lto

cd src; make all
make[1]: Entering directory '/var/tmp/portage/dev-util/gperf-3.1-r1/work/gperf-3.1/src'
x86_64-pc-linux-gnu-g++ -O2 -pipe -march=native -Werror=strict-aliasing -Werror=odr -Werror=lto-type-mismatch -flifetime-dse=1 -I. -I./../lib -c ./version.cc
x86_64-pc-linux-gnu-g++ -O2 -pipe -march=native -Werror=strict-aliasing -Werror=odr -Werror=lto-type-mismatch -flifetime-dse=1 -I. -I./../lib -c ./positions.cc
x86_64-pc-linux-gnu-g++ -O2 -pipe -march=native -Werror=strict-aliasing -Werror=odr -Werror=lto-type-mismatch -flifetime-dse=1 -I. -I./../lib -c ./options.cc
x86_64-pc-linux-gnu-g++ -O2 -pipe -march=native -Werror=strict-aliasing -Werror=odr -Werror=lto-type-mismatch -flifetime-dse=1 -I. -I./../lib -c ./keyword.cc
x86_64-pc-linux-gnu-g++ -O2 -pipe -march=native -Werror=strict-aliasing -Werror=odr -Werror=lto-type-mismatch -flifetime-dse=1 -I. -I./../lib -c ./keyword-list.cc
In file included from ./keyword-list.h:78,
                 from ./keyword-list.cc:22:
./keyword-list.icc: In member function ‘KeywordExt_List*& KeywordExt_List::rest()’:
./keyword-list.icc:50:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   50 |   return *reinterpret_cast<KeywordExt_List**>(&_cdr);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
make[1]: *** [Makefile:107: keyword-list.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make[1]: Leaving directory '/var/tmp/portage/dev-util/gperf-3.1-r1/work/gperf-3.1/src'
make: *** [Makefile:34: all] Error 2
 * ERROR: dev-util/gperf-3.1-r1::gentoo failed (compile phase):
 *   emake failed
 *
 * If you need support, post the output of `emerge --info '=dev-util/gperf-3.1-r1::gentoo'`,
 * the complete build log and the output of `emerge -pqv '=dev-util/gperf-3.1-r1::gentoo'`.
 * The complete build log is located at '/var/log/portage/dev-util:gperf-3.1-r1:20230115-225352.log'.
 * For convenience, a symlink to the build log is located at '/var/tmp/portage/dev-util/gperf-3.1-r1/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/dev-util/gperf-3.1-r1/temp/environment'.
 * Working directory: '/var/tmp/portage/dev-util/gperf-3.1-r1/work/gperf-3.1'
 * S: '/var/tmp/portage/dev-util/gperf-3.1-r1/work/gperf-3.1'

>>> Failed to emerge dev-util/gperf-3.1-r1, Log file:

[Comment 5 Pietro 2023-08-27 10:43:48 UTC]

Unfortunately I can reproduce the issue as well.

I created the following nolto.conf file and added the program in question to nolto.conf but made no difference

>>>
CFLAGS="${CFLAGS} -fno-lto"
CXXFLAGS="${CXXFLAGS} -fno-lto"
FCFLAGS="${FCFLAGS} -fno-lto"
FFLAGS="${FFLAGS} -fno-lto"
<<<

I am using the following COMMON_FLAGS in make.conf:
COMMON_FLAGS="-march=alderlake -O2 -pipe -flto -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing"

Any help to fix / bybass the error would be appreciated.

Thanks

[Comment 6 Kostadin Shishmanov 2023-08-27 10:54:25 UTC]

A workaround would be to make an env file which appends -fno-strict-aliasing for all the packages that fail because of that error until they are fixed upstream.

https://marc.info/?l=gentoo-dev&m=165639574126280&w=2