public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
* [Bug c++/104386] New: no_unique_address causes invalid member alignment of pod struct @ 2022-02-04 17:43 gcc at ebasoft dot com.pl 2022-02-04 21:55 ` [Bug c++/104386] " pinskia at gcc dot gnu.org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: gcc at ebasoft dot com.pl @ 2022-02-04 17:43 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104386 Bug ID: 104386 Summary: no_unique_address causes invalid member alignment of pod struct Product: gcc Version: 11.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: gcc at ebasoft dot com.pl Target Milestone: --- struct base { [[no_unique_address]] uint32_t x; std::byte v; }; struct foo : public base { std::byte z; }; gcc sizeof(foo) == 8 https://godbolt.org/z/G4Mo3PdKT clang sizeof(foo) == 12 https://godbolt.org/z/bdzvaMn9c As I was told it is gcc bug https://www.reddit.com/r/cpp/comments/sjx2mk/no_unique_addres_where_can_in_c_standard_instead/ [orbital1337]"Your class base is a POD but its not a POD for the purpose of layout (since it has potentially overlapping data members). Thus the Itanium ABI specifies that it's size without padding (dsize) should be set to its size with padding (sizeof). The first datamember of your class foo is put at dsize(base). clang does the right thing and puts it at an offset of 8 bytes whereas gcc ignores that one line of the specification and puts it at an offset of 5 bytes instead." ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/104386] no_unique_address causes invalid member alignment of pod struct 2022-02-04 17:43 [Bug c++/104386] New: no_unique_address causes invalid member alignment of pod struct gcc at ebasoft dot com.pl @ 2022-02-04 21:55 ` pinskia at gcc dot gnu.org 2022-02-06 10:26 ` gcc at ebasoft dot com.pl ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-02-04 21:55 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104386 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Hmm: https://github.com/itanium-cxx-abi/cxx-abi/issues/108 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/104386] no_unique_address causes invalid member alignment of pod struct 2022-02-04 17:43 [Bug c++/104386] New: no_unique_address causes invalid member alignment of pod struct gcc at ebasoft dot com.pl 2022-02-04 21:55 ` [Bug c++/104386] " pinskia at gcc dot gnu.org @ 2022-02-06 10:26 ` gcc at ebasoft dot com.pl 2022-02-06 23:10 ` pinskia at gcc dot gnu.org 2022-03-29 15:05 ` redi at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: gcc at ebasoft dot com.pl @ 2022-02-06 10:26 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104386 --- Comment #2 from Artur Bać <gcc at ebasoft dot com.pl> --- I think it is connected with this case https://godbolt.org/z/cvfs1KqGW https://godbolt.org/z/vdzTzo7be //sizeof(foo) ==12 struct base { uint32_t x{}; std::byte v{}; base() noexcept = default; }; struct foo : public base { std::byte z; }; //sizeof(foo) == 8 struct base { uint32_t x; std::byte v; base() noexcept : x{}, v{} {} }; struct foo : public base { std::byte z; }; and https://www.reddit.com/r/cpp/comments/slfugx/comment/hvs4n7j/?utm_source=share&utm_medium=web2x&context=3 "Som1Lse · 5 hr. ago Interestingly GCC disagrees with itself: -std=c++17 it considers base to be a POD and doesn't reuse padding. -std=c++20 it considers base to not be a POD and agrees with Clang, reusing the padding bytes." ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/104386] no_unique_address causes invalid member alignment of pod struct 2022-02-04 17:43 [Bug c++/104386] New: no_unique_address causes invalid member alignment of pod struct gcc at ebasoft dot com.pl 2022-02-04 21:55 ` [Bug c++/104386] " pinskia at gcc dot gnu.org 2022-02-06 10:26 ` gcc at ebasoft dot com.pl @ 2022-02-06 23:10 ` pinskia at gcc dot gnu.org 2022-03-29 15:05 ` redi at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-02-06 23:10 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104386 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |blocker ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/104386] no_unique_address causes invalid member alignment of pod struct 2022-02-04 17:43 [Bug c++/104386] New: no_unique_address causes invalid member alignment of pod struct gcc at ebasoft dot com.pl ` (2 preceding siblings ...) 2022-02-06 23:10 ` pinskia at gcc dot gnu.org @ 2022-03-29 15:05 ` redi at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: redi at gcc dot gnu.org @ 2022-03-29 15:05 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104386 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Status|UNCONFIRMED |NEW Last reconfirmed| |2022-03-29 ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-03-29 15:05 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-02-04 17:43 [Bug c++/104386] New: no_unique_address causes invalid member alignment of pod struct gcc at ebasoft dot com.pl 2022-02-04 21:55 ` [Bug c++/104386] " pinskia at gcc dot gnu.org 2022-02-06 10:26 ` gcc at ebasoft dot com.pl 2022-02-06 23:10 ` pinskia at gcc dot gnu.org 2022-03-29 15:05 ` redi at gcc dot gnu.org
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).