[dx12] Don't panic if `MaxSupportedFeatureLevel` wasn't set by query #8806

inner-daemons · 2026-01-03T08:38:33Z

Connections
Closes #8803

Description
Fixes issue with device not supporting our required D3D12 feature level, and us entering unreachable code. This is an issue for mozilla.

Testing
Hasn't been, @ErichDonGubler can you verify that this should fix it?

Squash or Rebase?
Squash due to only commit being named stupid

Checklist

Run cargo fmt.
Run taplo format.
Run cargo clippy --tests. If applicable, add:
- --target wasm32-unknown-unknown
Run cargo xtask test to run tests.
If this contains user-facing changes, add a CHANGELOG.md entry.

ErichDonGubler

Super minor changes requested. Otherwise, thanks for taking this on! 🙂

wgpu-hal/src/dx12/adapter.rs

ErichDonGubler · 2026-01-03T19:24:35Z

wgpu-hal/src/dx12/adapter.rs

            Direct3D::D3D_FEATURE_LEVEL_12_0 => FeatureLevel::_12_0,
            Direct3D::D3D_FEATURE_LEVEL_12_1 => FeatureLevel::_12_1,
            Direct3D::D3D_FEATURE_LEVEL_12_2 => FeatureLevel::_12_2,
+            Direct3D::D3D_FEATURE_LEVEL(0) => return None,


issue(non-blocking): I suspect we'll also want to report this via telemetry. That sound interesting, @teoxoy?

I doubt this will be worth reporting given my comment below. Also completely out of my domain of expertise lol. Seems to be an issue with some windows versions that is easily bypassed.

I'll leave this unresolved for visibility

I think it would be good to have telemetry for this since it should count towards the "total nr of people without D3D12" counter. I can also open another PR for it.

CHANGELOG.md

ErichDonGubler · 2026-01-03T19:31:42Z

In the OP:

This is an issue for mozilla.

This is an issue for everyone trying to use wgpu on native, Mozilla is just the first to discover it. 😉

ErichDonGubler · 2026-01-03T19:33:14Z

Hasn't been, @ErichDonGubler can you verify that this should fix it?

We don't have 100% certainty that the case we're trying to handle is the actual behavior causing crashes here (viz., we're not sure that 0 is actually the value remaining in MaxSupportFeatureLevel). I believe this is the case, but it would be best if we could find a way to reproduce this before merging.

inner-daemons · 2026-01-03T19:35:32Z

@ErichDonGubler I asked in the directx discord. I'm told that what we're seeing "shouldnt be possible" but also isn't a driver bug; the person is responding with single sentences and I can't figure out what they mean. Once I get feedback I'll also document that here in a comment.

ErichDonGubler · 2026-01-03T20:03:58Z

Inlining my notes from bug 2007754, comment 7:

I just tested on a Windows machine of mine that doesn't support Direct3D::D3D_FEATURE_LEVEL_12_2 by commenting all but the Direct3D::D3D_FEATURE_LEVEL_12_2 member of the d3d_feature_level array … . In that case, CheckFeatureSupport does return an E_INVALIDARG. 🫠 … I wonder if this is a bug … that got fixed in newer versions of DX12 than what user machines currently have?

ETA: For reference, that's this commit stack: https://github.com/gfx-rs/wgpu/compare/aba9161b72c028aa8a1ce15aabd92e3c3cdb2da3..6fe22a0b59f256648eedd7652247c23490162d1a

jimblandy · 2026-01-06T22:42:49Z

Hasn't been, @ErichDonGubler can you verify that this should fix it?

We don't have 100% certainty that the case we're trying to handle is the actual behavior causing crashes here (viz., we're not sure that 0 is actually the value remaining in MaxSupportFeatureLevel). I believe this is the case, but it would be best if we could find a way to reproduce this before merging.

@ErichDonGubler So, were you able to get a crash locally with the test case in #8803? Does this PR fix that crash?

inner-daemons · 2026-01-06T23:11:32Z

Also, I will update this with information from the DX12 discord server:

This is a bug in Microsoft's DirectX code on older Windows versions. The fix is just as I did it here, and some sample code shared by several users had basically identical code to what we would have after this lands.

I'd still like confirmation that this actually fixes the bug but I'd be very surprised if it didn't.

Co-authored-by: Erich Gubler <erichdongubler@gmail.com>

teoxoy · 2026-01-07T18:07:07Z

Also, I will update this with information from the DX12 discord server:

This is a bug in Microsoft's DirectX code on older Windows versions. The fix is just as I did it here, and some sample code shared by several users had basically identical code to what we would have after this lands.

Thanks for tracking this down!

teoxoy · 2026-01-07T18:10:24Z

Actually, does the 0 mean that the device supports FL11 or does it mean the device doesn't support D3D12 at all? I'm asking because creating the D3D12 succeeded (which has a minimum FL requirement of 11) and the old code (before #8576) didn't run into issues.

inner-daemons · 2026-01-07T18:31:48Z

Well we set the value to zero before calling the DirectX function, so I'm actually not sure if a value of zero indicates nothing being written or a zero being written by the driver. It shouldn't really matter though.

I'm pretty sure we should treat DX12 as being unsupported if it returns zero. It would return one of the feature levels that we pass it if it actually supported one of them. This is what the code from other projects that I've seen does, just throws away those devices.

I'm honestly a little surprised that the old code didn't run into issues, but I don't think that means we should assume it supports a feature level that it explicitly doesn't claim to.

teoxoy · 2026-01-08T11:31:59Z

I looked at Firefox's crash stats and if you aggregate them by "platform version" here, there are crashes even on 10.0.26200 (Windows 11 25H2).

There is also another issue (crash stats) introduced by #8576 where we now always .unwrap() here:

wgpu/wgpu-hal/src/dx12/adapter.rs

Line 74 in bf075e7

    
           unsafe { adapter.CheckInterfaceSupport(&Dxgi::IDXGIDevice::IID) }.unwrap() as u64;

This seemed fine to do since CheckInterfaceSupport is not documented to return 0x887A0005 but it seems it does...

teoxoy · 2026-01-08T11:34:43Z

I'll put up a PR solving these 2 issues and adding telemetry as well.

inner-daemons added 4 commits January 3, 2026 02:34

Will this fix?

c001579

Lmao I need to go to bed

ab2dceb

Maybe this'll work

cfbffe2

Added changelog entry

f3a3a46

ErichDonGubler reviewed Jan 3, 2026

View reviewed changes

ErichDonGubler changed the title ~~Fix #8803~~ [dx12] Don't panic if MaxSupportedFeatureLevel wasn't set by query Jan 3, 2026

inner-daemons and others added 3 commits January 6, 2026 17:23

Update CHANGELOG.md

6f6371b

Co-authored-by: Erich Gubler <erichdongubler@gmail.com>

Added a comment and addressed Erich's suggestion

c655baf

Merge remote-tracking branch 'upstream/trunk' into fix-8803

9e82d0f

inner-daemons requested a review from ErichDonGubler January 6, 2026 23:26

cwfitzgerald assigned ErichDonGubler Jan 7, 2026

Merge branch 'trunk' into fix-8803

aafe2f6

teoxoy mentioned this pull request Jan 8, 2026

[d3d12] fix panics in adapter creation #8845

Merged

ErichDonGubler closed this in #8845 Jan 8, 2026

[dx12] Don't panic if MaxSupportedFeatureLevel wasn't set by query #8806

[dx12] Don't panic if MaxSupportedFeatureLevel wasn't set by query #8806

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[dx12] Don't panic if `MaxSupportedFeatureLevel` wasn't set by query #8806

[dx12] Don't panic if `MaxSupportedFeatureLevel` wasn't set by query #8806

inner-daemons commented Jan 3, 2026 •

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