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Fix regression from #8058 #8181

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kamil-tekiela
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@kamil-tekiela kamil-tekiela commented Mar 7, 2022

This is partially reversing my previous change from 93a8d5c.
The fix remains in place, but we must keep the memory copying.

@kamil-tekiela kamil-tekiela marked this pull request as ready for review March 7, 2022 12:43
@kamil-tekiela kamil-tekiela marked this pull request as draft March 7, 2022 12:44
@kamil-tekiela kamil-tekiela marked this pull request as ready for review March 7, 2022 13:55
@kamil-tekiela kamil-tekiela changed the base branch from master to PHP-8.0 March 7, 2022 13:55
@kamil-tekiela kamil-tekiela reopened this Mar 7, 2022
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cmb69 commented Mar 30, 2022

Why do we need to keep the memory copying? Can any malfunction be reproduced? If so, adding a test case would probably be a good idea.

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Why do we need to keep the memory copying? Can any malfunction be reproduced? If so, adding a test case would probably be a good idea.

It's needed to get rid of use-after-free errors that are plaguing CI. I am not sure if it actually causes a difference in behaviour as I haven't observed any and I didn't notice any new issues being raised about it. See https://dev.azure.com/phpazuredevops/PHP/_build/results?buildId=23771&view=ms.vss-test-web.build-test-results-tab

After 23 days I forgot the details of my debugging, but if I remember correctly, depending on how the prepare is called, we might expect mysqli to free the object or not. Thus, mysqlnd can't do it in place and has to first create successfully a new PS and then swap it and destroy the old one. I don't have the time to start a debugger now to collect details, but this should fix the use-after-free and not change anything in the behaviour. I don't think we can catch this in tests.

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Thanks for the explanation!

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cmb69 commented Mar 31, 2022

@kamil-tekiela, it seems the PHP-8.1 and master builds are failing now; can you please have a look?

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Thanks, I forgot to change the two lines when merging. It should be all green now.

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