Bug 855662 – dev-lang/yap-7.1.0 fails to compile (lto): exec.c:982:7: error: type of MkErrorTerm does not match original declaration [-Werror=lto-type-mismatch]

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

[Description Agostino Sarubbo 2022-07-02 07:21:49 UTC]

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

Issue: dev-lang/yap-7.1.0 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 2022-07-02 07:21:51 UTC]

Created attachment 789428 [details]
build.log

build log and emerge --info

[Comment 2 Agostino Sarubbo 2022-07-02 07:21:53 UTC]

Error(s) that match a know pattern in addition to what has been reported in the summary:


FAILED: libYap.so.7.1.0 
/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/exec.c:982:7: error: type of ‘MkErrorTerm’ does not match original declaration [-Werror=lto-type-mismatch]

[Comment 3 Agostino Sarubbo 2022-07-26 09:00:54 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 2024-08-14 04:37:35 UTC]

/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/exec.c:982:7: error: type of ‘MkErrorTerm’ does not match original declaration [-Werror=lto-type-mismatch]
  982 |   e = MkErrorTerm(&old);
      |       ^
/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/errors.c:1266:6: note: return value type mismatch
 1266 | Term MkErrorTerm(yap_error_descriptor_t *t)
      |      ^
/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/errors.c:1266:6: note: type ‘Term’ should match type ‘int’
/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/errors.c:1266:6: note: ‘MkErrorTerm’ was previously declared here



And if you build with GCC 14 or the relevant Modern C -Werror flags, this actually fails to build at all:

FAILED: CMakeFiles/libYap.dir/C/exec.c.o
/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/exec.c: In function ‘watch_retry’:
/var/tmp/portage/dev-lang/yap-7.1.0/work/yap-7.1.0/C/exec.c:982:7: error: implicit declaration of function ‘MkErrorTerm’ [-Werror=implicit-function-declaration]
  982 |   e = MkErrorTerm(&old);
      |       ^~~~~~~~~~~
cc1: some warnings being treated as errors

So this is a Modern C porting issue that is then resulting in an LTO type mismatch because the implicit function declaration produces the wrong type.