Issues with preserve_most?

[ClearScript Developers]

Greetings!

We've noticed that preserve_most was disabled for Windows/arm64 on the 11.1 branch tip today.

We'd actually been struggling with extreme instability in 11.1 release builds on Linux x64, so we tried disabling preserve_most for all platforms, and, surprisingly, that seems to have stabilized our Linux builds completely.

So, it would appear that preserve_most issues go beyond Windows/arm64. In case it matters, we do use a relatively old toolchain to preserve compatibility with older distros.

Anyone have any other experiences with preserve_most?

[Jakob Gruber]

+cle...@chromium.org 

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[Clemens Backes]

Thanks for reaching out! Indeed, preserve_most support turned out to be a bit incomplete, so we tried to restrict it to the most important platforms and toolchains used for Chromium. It's restricted to clang anyway, and I didn't find any relevant fixes since the introduction in 2016. Which toolchain do you use where you see crashes? Maybe we can restrict it further to the most recent clang versions.

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Clemens Backes

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[ClearScript Developers]

Hi Clemens,

>Which toolchain do you use where you see crashes?

Our hack to retain compatibility with old distros is probably bogus and unsupported, so if you know of a better way, please share it :)

Anyway, what we (try to) do is roll back V8's Linux build tools to their state as of the last version that supported Ubuntu 16.04 LTS with glibc-2.23. After running "gclient sync" normally, we reset the "build" and "tools/clang" repositories to specific commits, then use install-sysroot to install specific "last known good" sysroots.

Cheers! 

[Clemens Backes]

On Wed, Feb 8, 2023 at 6:05 PM ClearScript Developers <clearsc...@gmail.com> wrote:

Hi Clemens,

>Which toolchain do you use where you see crashes?

Our hack to retain compatibility with old distros is probably bogus and unsupported, so if you know of a better way, please share it :)

Anyway, what we (try to) do is roll back V8's Linux build tools to their state as of the last version that supported Ubuntu 16.04 LTS with glibc-2.23. After running "gclient sync" normally, we reset the "build" and "tools/clang" repositories to specific commits, then use install-sysroot to install specific "last known good" sysroots.

That indeed sounds like a case we don't really want to encourage :D 

Anyway, we just landed a CL to restrict the use of preserve_most to clang 17, which has a fix which we will start to rely on (https://reviews.llvm.org/D143425). That should also fix your use case.

Do you need us to merge that back to v8 11.1, or can you just disable that on your side until you upgrade to a recent version of v8?

 

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[ClearScript Developers]

Hi Clemens,

>Do you need us to merge that back to v8 11.1, or can you just disable that on your side until you upgrade to a recent version of v8?

 

There's no need to merge the fix back to v8 11.1, as we've added preserve_most disablement to our set of V8 patches.

Thanks again!