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Fix statics issue with barriers #108311

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davidwrighton
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@davidwrighton davidwrighton commented Sep 27, 2024

A barrier based approach for fixing issue #105441

This adds barriers after all the places outside of jitted code where we check to see if the class constructor is initialized. These barriers are somewhat non-optimal on ARM64, as they use ldar instead of ldapr, but should fix the problems we've been encountering with regards to memory model behavior around statics.

@@ -653,7 +653,8 @@ DynamicHelper DynamicHelperFrameFlags_ObjectArg | DynamicHelperFrameFlags_Object

LEAF_ENTRY JIT_GetDynamicNonGCStaticBase_SingleAppDomain, _TEXT
// If class is not initialized, bail to C++ helper
ldr x1, [x0, #OFFSETOF__DynamicStaticsInfo__m_pNonGCStatics]
add x1, x0, #OFFSETOF__DynamicStaticsInfo__m_pNonGCStatics
ldar x1, [x1]
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Do we need the barriers in arm32 version of these helpers as well?

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(And also riscv and loongarch.)

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Yes we do, this was more intended to get a quick bit written up so that we could run some tests.

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NOTE: can be ldapur x1, [x1, #OFFSETOF__DynamicStaticsInfo__m_pGCStatics] for macos-arm64 since that has rcpc2 in the baseline, but not sure it worth the complexity.

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Also, it's a detail that we will be able to do a better job of implementing these helpers when we move them to managed. (Since the jit will take advantage of the ldapr or ldapur instructions instead of just using ldar which is a stronger barrier than we need.)

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Finally, there is no need to fix arm, as we don't have handwritten assembly helpers for this set of helpers.

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@davidwrighton davidwrighton marked this pull request as ready for review September 27, 2024 16:18
@davidwrighton davidwrighton merged commit 2fcc09b into dotnet:main Sep 27, 2024
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/backport to release/9.0

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Started backporting to release/9.0: https://github.com/dotnet/runtime/actions/runs/11076638514

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@davidwrighton backporting to release/9.0 failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Fix statics issue with barriers
Applying: Add barriers for RiscV and Loongson
Using index info to reconstruct a base tree...
M	src/coreclr/vm/loongarch64/asmhelpers.S
M	src/coreclr/vm/riscv64/asmhelpers.S
Falling back to patching base and 3-way merge...
Auto-merging src/coreclr/vm/riscv64/asmhelpers.S
CONFLICT (content): Merge conflict in src/coreclr/vm/riscv64/asmhelpers.S
Auto-merging src/coreclr/vm/loongarch64/asmhelpers.S
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0002 Add barriers for RiscV and Loongson
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!

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@davidwrighton an error occurred while backporting to release/9.0, please check the run log for details!

Error: git am failed, most likely due to a merge conflict.

davidwrighton added a commit to davidwrighton/runtime that referenced this pull request Sep 27, 2024
* Fix statics issue with barriers

* Add barriers for RiscV and Loongson
sirntar pushed a commit to sirntar/runtime that referenced this pull request Sep 30, 2024
* Fix statics issue with barriers

* Add barriers for RiscV and Loongson
jeffschwMSFT added a commit that referenced this pull request Oct 3, 2024
* Fix statics issue with barriers

* Add barriers for RiscV and Loongson

Co-authored-by: Jeff Schwartz <[email protected]>
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3 participants