Adreno 840 (SD 8 Elite Gen 5 / Galaxy S26+): stock-driver fallback needed; then SIGBUS in DxvkMemoryAllocator on first UI draw

[KLCLAU]

Adreno 840 (Snapdragon 8 Elite Gen 5 / Galaxy S26+): SIGBUS in DxvkMemoryAllocator after forcing stock-driver fallback

Device

• Galaxy S26+ SM-S942W, Android 16, kernel 6.12.30-android16
• SoC Snapdragon 8 Elite Gen 5 (SM8850), Adreno 840, stock driver 0842.19.8 (Vulkan 1.3, textureCompressionBC present)
• APK: GeneralsZH-Android-android-v0.1.0-debug.apk (Beta release android-v0.1.0)

Summary

The bundled Turnip vulkan.ad07xx.so enumerates 0 physical devices on Adreno 840
(DxvkInstance::enumAdapters: Failed to enumerate adapters), so the app dies at
TheDisplay->init().

Forcing the stock-driver path (documented in the renderer-research doc as the rung-1
fallback for Adreno 8xx) by making gxSetupTurnipDriver()'s staged copy fail
(GENERALSX_TURNIP_* env left unset) gets much further: Vulkan + swapchain come up
on the stock driver, all shaders compile, the engine enters the render loop and renders
frames — then crashes with SIGBUS (BUS_ADRALN) in DXVK on the first UI draw.

Crash (stock-driver path)

Fatal signal 7 (SIGBUS), code 1 (BUS_ADRALN), fault addr 0x…47f  (4-byte-unaligned), tid SDLThread
#00 __aarch64_ldadd4_acq                                   libdxvk_d3d9.so
#01 dxvk::DxvkMemoryAllocator::allocateMemory(VkMemoryRequirements const&, dxvk::DxvkAllocationInfo const&)+908
#02 dxvk::DxvkMemoryAllocator::createBufferResource(...)+176
#03 dxvk::D3D9ConstantBuffer::AllocSlice()+148
#04 dxvk::D3D9DeviceEx::UpdateFixedFunctionVS()+1396
#05 dxvk::D3D9DeviceEx::PrepareDraw(...)+2512
#06 dxvk::D3D9DeviceEx::DrawIndexedPrimitive(...)+168
#07 dxvk::D3D8Device::DrawIndexedPrimitive(...)+132
#08 DX8Wrapper::Draw(...)                                   libmain.so
#09 Render2DClass::Render()+1444
#10 W3DDisplay::onFlush()+40
#11 W3DDisplayString::draw(...)+636
#12 InGameUI::drawRenderFps(int&, int&)+372
#13 InGameUI::postWindowDraw()+124
#14 W3DInGameUI::draw() … GameClient::update() … SDL3GameEngine::execute() … SDL_main

__aarch64_ldadd4_acq is a 4-byte atomic add; the fault address is not 4-byte aligned,
so an atomic counter inside DxvkMemoryAllocator (DXVK 2.6.0, aarch64 clang 18) is being
placed/accessed unaligned on ARM64.

Also seen (stock-driver path)

Endless Presenter: Got VK_SUBOPTIMAL_KHR, recreating swapchain (portrait 1080x2340
panel, app renders 2340x1080) — surfaceTransform / pre-rotation not handled; the
swapchain is recreated every frame.

Asks

1. Wire up the rung-1 stock-driver path for Adreno 8xx so vulkan.ad07xx.so isn't
   force-loaded when it enumerates no adapters (fall back instead of throwing), or ship
   an a8xx-capable Turnip.
2. The DxvkMemoryAllocator unaligned-atomic SIGBUS on ARM64.
3. Handle VK_SUBOPTIMAL_KHR / surfaceTransform without a per-frame recreate loop.

Happy to run more captures — full logcat + tombstone available.

[KLCLAU]

Update — it works. Built the port from source (HEAD 8d53e7d, NDK r27c) with two fixes and it now boots to the main menu and plays a skirmish at ~30 FPS on the Galaxy S26+ (Adreno 840).

The SIGBUS is gone on HEAD

The DxvkMemoryAllocator::allocateMemory → __aarch64_ldadd4_acq BUS_ADRALN crash from the Beta 18 APK does not reproduce on current main. It was not a 16 KB-page issue (this device runs a 4 KB-page kernel). Something between Beta 18 and HEAD fixed it — the fix(android): disable backface culling for 2D UI quads (DXVK winding) commit is the likely candidate, since the crash was in the Render2DClass::Render → InGameUI::drawRenderFps path.

Two fixes needed on top

1. Stock-driver fallback for Adreno 8xx → fix(android): fall back to stock Vulkan driver on Adreno 8xx (Snapdragon 8 Elite / S25-S26) #24
   vulkan.ad07xx.so loads but enumerates 0 devices on a840 → enumAdapters: Failed to enumerate adapters. Patch parses /sys/class/kgsl/kgsl-3d0/gpu_model and skips Turnip for series ≥ 8 so the loader uses the stock driver (Vulkan 1.3 + BCn native on a8xx — the rung 1 path from the research doc).

2. VK_SUBOPTIMAL_KHR swapchain-recreate-per-frame loop → fix(android): treat VK_SUBOPTIMAL_KHR as success in the presenter dxvk#1
   Portrait surface + landscape render → currentTransform never matches preTransform → 761 recreating swapchain in 45 s. Patch treats SUBOPTIMAL as success on Android (compositor does the rotation). 761 → 0.

Build-tree note (not in the PRs)

cmake --preset android-vulkan fails at cmake/dx8.cmake for me:

CMake Error at cmake/dx8.cmake:328 (message):
  Failed to apply Patches/dxvk-android.patch to references/fadi-labib-dxvk

The pinned references/fadi-labib-dxvk commit (78c2ce1) already contains Patches/dxvk-android.patch in its tree (the vulkan_loader.cpp hunk especially — the gate Turnip on /dev/kgsl-3d0 commit rewrote that region), so a plain git apply fails on context drift and the reverse-check misses it. Worked around locally by dropping the redundant vulkan_loader.cpp hunk from the patch and using git apply --3way; the real fix is probably to regenerate dxvk-android.patch against the current pinned commit, or drop the hunks that are now committed.

Still open

• Touch menu-navigation is unreliable (taps don't reliably hit UI buttons) — separate from this issue.
• Shell map can go black after a forced orientation change.

Happy to help land any of this.