Bug #79356 [Asn->Csd]: FFI:structure/union alignment [ext/ffi/tests/022.phpt] failure

[email protected]
Newsgroups php.bugs,php.qa
Message-ID <[email protected]>
Edit report at https://bugs.php.net/bug.php?id=79356&edit=1

 ID:                 79356
 Updated by:         [email protected]
 Reported by:        vibhutisawant18 at gmail dot com
 Summary:            FFI:structure/union alignment
                     [ext/ffi/tests/022.phpt] failure
-Status:             Assigned
+Status:             Closed
 Type:               Bug
 Package:            Testing related
 Operating System:   Ubuntu 16.04
 PHP Version:        master-Git-2020-03-09 (Git)
 Assigned To:        dmitry
 Block user comment: N
 Private report:     N

 New Comment:

ext/ffi/tests/022.phpt failure is fixed by exporting FFI::__BIGGEST_ALIGNMENT__ constant.

Anyway, __attribute__((aligned)) without argument may cause invalid alignment assumption, if library and PHP were compiled with different options. The same situation with C.


Previous Comments:
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[2020-03-11 12:34:34] [email protected]

@nikic: I don't know, but in case GCC supports this, I would prefer to support this as well. 

The proposed fix https://github.com/php/php-src/pull/5256

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[2020-03-11 09:11:56] [email protected]

@dmitry: Do you know of some particular case where this is being used?

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[2020-03-11 09:07:00] [email protected]

I'm not sure, if we should remove support for __attribute__((aligned)) without specified alignment completely. Probably, we should export __BIGGEST_ALIGNMENT__ constant and may be add a warning about dependency.

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[2020-03-09 10:24:04] [email protected]

@dmitry: I would suggest that we remove support for __attribute__((aligned)) without specified alignment, because it is not interoperable. If PHP was combined with a different target architecture than the library we're linking against, the alignment will be incorrect. We should force an explicit specification of the alignment instead. What do you think?

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[2020-03-09 10:21:18] [email protected]

Okay, I see now. __attribute__((aligned)) is the same as __attribute__((__BIGGEST_ALIGNMENT__)). I happened to use an -march=sandybridge build, where __BIGGEST_ALIGNMENT__ is 32.

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