[cfe-dev] ModuleCache issues on Linux (Ubuntu)

[David Blaikie via cfe-dev]

Can't say any of this sounds especially familiar to me - cc'd a few folks
who might have some context.

On Fri, Feb 19, 2021 at 6:28 AM Ilya Kuteev via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hello everyone!
>
> I've ran into a strange problem using clang-modules on Linux. I have a Linux machine running Ubuntu 18.04.4 LTS.
>
> When I put my ModuleCache on RAM everything is OK
>
> When I put ModuleCache on SSD/HDD, very frequently I'm getting different errors with pcm files, like below:
>
> ```
>
> fatal error: module file '/home/ilyakuteev/module_cache/2/1721172304169885905/3OA4HVRBFA8AJ/Base-5W2XL4QH4QAH.pcm' is out of date and needs to be rebuilt: signature mismatch
>
> ```
>
>
> ```
>
> fatal error: malformed or corrupted AST file: 'Unexpected end of file reading 4154469704 of 4738416 bytes'
>
> note: after modifying system headers, please delete the module cache at '/home/ilyakuteev/module_cache/1721172304169885905/37WO4K6LHZNB5'
>
> fatal error: error in backend: Invalid abbrev number
>
> ```
>
>
> ```
>
> fatal error: malformed or corrupted AST file: 'declaration ID out-of-range for AST file'
>
> note: after modifying system headers, please delete the module cache at '/home/ilyakuteev/module_cache/3/1721172304169885905/1907ERGA34IRD'
>
> ```
>
>
> I’ve done some research and it looks like the failure is inside single clang process, clang writes pcm down on disk, then reads it and gets a malformed file back, or some other problem with reading on-disk pcm.
>
>
> I've found a patch https://reviews.llvm.org/D22636 and it looks like it fixes my problems, but I don’t want to use it, cause it just rebuilts "owned" module if its AST is corrupted and looks like retry of operation, not a real fix. Also this fix introduces some unstable behavior.
>
>
> My questions:
>
> 1) Is this a known problem?
>
> 2) How can I safely hot-fix it before it will be fixed in clang?
>
> 3) Do I need to provide more logs for this issue to be fixed?
>
>
> Thanks
>
>
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