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Re: Finalizing 'inhibit-automatic-native-compilation'

From: Stefan Monnier
Subject: Re: Finalizing 'inhibit-automatic-native-compilation'
Date: Mon, 20 Feb 2023 07:48:29 -0500
User-agent: Gnus/5.13 (Gnus v5.13)

>> `make-temp-name` uses `O_EXCL | O_CREAT` so as to close the race
>> condition: if someone predicated the filename, we detect it atomically
>> and we try again.
>> You might like to check
>> https://wiki.sei.cmu.edu/confluence/display/c/FIO21-C.+Do+not+create+temporary+files+in+shared+directories
> Thanks for the pointer.
> I'm still not really convinced we have a problem here with trampolines.
> With `make-temp-file' we are really only choosing the filename and
> suggesting it to libgccjit, this last one will perform the file
> creation.

The important part is the use of `O_EXCL | O_CREAT` when creating
the file.
*BUT* `O_EXCL | O_CREAT` will fail if the file already exists.  Which is
why `make-temp-file` needs `make-temp-name` to generate new names until
we find one that really doesn't exist (not just at the time
`make-temp-name` is called but the fraction of a millisecond later when
we do try to create it).

> I'd be surprised if GCC does not handle this correctly, and
> in case shouldn't this be a GCC bug?

I'd be surprised.  If you tell it to write to a pre-existing file, does
it fail with an error?  If not, then I think it can't be used safely unless
*you* pre-create the file (e.g. with `make-temp-file`).


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