Bring throw helpers to PUSH_COOP_PINVOKE_FRAME plan #123015

am11 · 2026-01-08T22:04:27Z

Fixes #116375.

dotnet-policy-service · 2026-01-08T22:05:36Z

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src/coreclr/vm/jithelpers.cpp

src/coreclr/pal/inc/unixasmmacrosamd64.inc

src/coreclr/vm/jithelpers.cpp

src/coreclr/pal/inc/unixasmmacrosamd64.inc

This reverts commit af084b8.

Added MXCSR reset to prevent floating point exceptions during JIT compilation on AMD64 Windows.

am11 · 2026-01-13T14:34:38Z

@janvorli, JIT/Directed, JIT/CodeGenBringUpTests and Exceptions suites are now passing. I cannot repro the remaining win-x64 failures like add_r4:

# in powershell
> ./build.cmd clr+libs -rc Checked
> src/tests/build.cmd Checked -Dir JIT/Directed -Dir JIT/CodeGenBringUpTests -Dir Exceptions -Dir JIT/IL_Conformance /p:LibrariesConfiguration=Debug
> $CORE_ROOT=$env:CORE_ROOT="$pwd/artifacts/tests/coreclr/windows.x64.Debug/Tests/Core_Root"
> artifacts\tests\coreclr\windows.x64.Checked\JIT\IL_Conformance\IL_Conformance\IL_Conformance.cmd
...
END EXECUTION - PASSED
PASSED

CI is showing https://helix.dot.net/api/2019-06-17/jobs/36ba1a26-3370-47a0-a24a-e0b2d2e41006/workitems/IL_Conformance/console:

13:15:59.276 Running test: JIT/IL_Conformance/Old/Conformance_Base/add_ovf_u8/add_ovf_u8.dll
13:15:59.281 Passed test: JIT/IL_Conformance/Old/Conformance_Base/add_ovf_u8/add_ovf_u8.dll
13:15:59.402 Running test: JIT/IL_Conformance/Old/Conformance_Base/add_r4/add_r4.dll
Xunit.Sdk.EqualException: Assert.Equal() Failure: Values differ
Expected: 100
Actual:   0
   at Xunit.Assert.Equal[T](T expected, T actual, IEqualityComparer`1 comparer) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/EqualityAsserts.cs:line 174
   at Program.<<Main>$>g__TestExecutor10|0_11(StreamWriter tempLogSw, StreamWriter statsCsvSw, <>c__DisplayClass0_0&)
13:16:00.027 Failed test: JIT/IL_Conformance/Old/Conformance_Base/add_r4/add_r4.dll
13:16:00.039 Running test: JIT/IL_Conformance/Old/Conformance_Base/add_r8/add_r8.dll
Xunit.Sdk.EqualException: Assert.Equal() Failure: Values differ
Expected: 100
Actual:   0
   at Xunit.Assert.Equal[T](T expected, T actual, IEqualityComparer`1 comparer) in /_/src/arcade/src/Microsoft.DotNet.XUnitAssert/src/EqualityAsserts.cs:line 174
   at Program.<<Main>$>g__TestExecutor11|0_12(StreamWriter tempLogSw, StreamWriter statsCsvSw, <>c__DisplayClass0_0&)
13:16:00.050 Failed test: JIT/IL_Conformance/Old/Conformance_Base/add_r8/add_r8.dll
13:16:00.063 Running test: JIT/IL_Conformance/Old/Conformance_Base/beq_r4/beq_r4.dll
13:16:00.241 Passed test: JIT/IL_Conformance/Old/Conformance_Base/beq_r4/beq_r4.dll

am11 · 2026-01-13T15:57:39Z

OK with $env:DOTNET_TieredCompilation=0 it fails locally. Investigating..

src/coreclr/vm/amd64/AsmMacros.inc

janvorli · 2026-01-13T22:19:48Z

src/coreclr/vm/excep.cpp

+
+#ifdef UNIX_AMD64_ABI
+    // On Unix AMD64, argument registers are saved in the transition block
+    m_Context.Rax = 0;


We need to store non-volatile registers and control registers only. The EH should not need anything else. So on Unix, we don't need the float state at all. And the general purpose argument registers are also not needed.

I'm going by #116375 (comment), which is why I added FP registers (and took a while to figure out the right restore points). Do you want me to revert FP registers and use PROLOG_WITH_TRANSITION_BLOCK ? I can test if it's sufficient for unwind. Note that we are replacing PAL_VirtualUnwind call in excep.cpp, where libunwind does account for FP registers.

My comment was on Unix Amd64 only. Other architectures need to restore some float registers, as they are non-volatile there. Only Unix Amd64 has no non-volatile FP regs.
So for Unix Amd64, let's not capture any FP regs and let's not copy them here - and thus not set the CONTEXT_FLOATING_POINT in the ContextFlags.

janvorli · 2026-01-13T23:08:16Z

src/coreclr/vm/amd64/Context.asm

+        ; which can corrupt MXCSR (setting it to 0x20 with all FP exception masks cleared).
+        ; Without this reset, FP operations after exception handling would trigger exceptions.
+        ; 0x1F80 = default MXCSR: all exception masks set, round to nearest, no exceptions pending
+        push    1F80h


I am not aware of any case that would have the CONTEXT_FLOATING_POINT set and not have the MXCSR valid in the CONTEXT. We've never had such a problem and you have initialization of that in your new code to update CONTEXT from the TransitionFrame.

Without 22571b2 and dd15723, one or more tests in JIT/Directed, JIT/CodeGenBringUpTests and Exceptions were failing (#123015 (comment)).

I think the problem is likely caused by something else. I don't see how your change (as a whole) could introduce such a problem.

jkotas · 2026-01-14T00:52:21Z

src/coreclr/vm/prestub.cpp

    PCODE pbRetVal = (PCODE)NULL;

+#if defined(TARGET_AMD64) && defined(TARGET_WINDOWS)
+    // Reset MXCSR to default value to prevent FP exceptions during JIT compilation.


If we have a problem with MXCSR getting messed up, it is not sufficient to reset it in prestub. We need to reset it earlier before resuming execution of managed code.

I've moved it to CallEHFilterFunclet.

github-actions bot added the area-VM-coreclr label Jan 8, 2026

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Jan 8, 2026

am11 force-pushed the feature/il_throw_PUSH_COOP_PINVOKE_FRAME branch from 1a243a6 to 00c4f6a Compare January 8, 2026 22:39

Bring throw helpers to PUSH_COOP_PINVOKE_FRAME plan

eb6c689

am11 force-pushed the feature/il_throw_PUSH_COOP_PINVOKE_FRAME branch from b8782d2 to 0d677dd Compare January 8, 2026 22:41

Handle FP regs

5359b4c

am11 force-pushed the feature/il_throw_PUSH_COOP_PINVOKE_FRAME branch from 0d677dd to 5359b4c Compare January 8, 2026 22:42

am11 added 2 commits January 9, 2026 01:11

.

cbb9238

wasm

b4a3ab2

build-analysis bot mentioned this pull request Jan 9, 2026

iOS.Device test WorkItemExecutions #122874

Open

am11 added 2 commits January 9, 2026 11:02

arm et al.

7df98b1

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

14e1537

am11 added 2 commits January 9, 2026 15:22

Account for FP callee-saved regs

fef4204

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4835a5f

jkotas reviewed Jan 9, 2026

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am11 added 2 commits January 10, 2026 18:17

.

2746edf

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

95c39e5

jkotas reviewed Jan 10, 2026

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fixes and reverts

2450d88

build-analysis bot mentioned this pull request Jan 10, 2026

LibraryImportGenerator.Unit.Tests crashing on linux-x64 mono interpreter #100800

Open

am11 added 4 commits January 11, 2026 11:05

[x64] unix: fix alignment, win: test a random thought

7fe9c53

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

bd342cf

linux-x64 fixes

e8287a5

linux-x64

8e7a5ff

jkotas reviewed Jan 11, 2026

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linux-arm32

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janvorli reviewed Jan 12, 2026

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janvorli reviewed Jan 12, 2026

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am11 added 11 commits January 12, 2026 18:00

Revert

bf0e4c5

Switch to reusing PROLOG_WITH_TRANSITION_BLOCK

af084b8

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

17845a5

Revert "Switch to reusing PROLOG_WITH_TRANSITION_BLOCK"

b5e6e6e

This reverts commit af084b8.

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

40313c1

Address RBP feedback

0147c5c

Prevent FP exceptions during JIT on AMD64 Windows

22571b2

Added MXCSR reset to prevent floating point exceptions during JIT compilation on AMD64 Windows.

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

fa44e1e

Remove obsolete comment (now that Init() is gone)

b109060

Enhance Context.asm with MXCSR reset explanation

dd15723

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

3c35b1b

build-analysis bot mentioned this pull request Jan 13, 2026

Sometimes the helix SDK uses GetWorkItemsAsync when workitems aren't done processing. dotnet/dnceng#6011

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3 tasks

jkotas reviewed Jan 13, 2026

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am11 added 2 commits January 13, 2026 23:08

Address fb

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Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

366421c

janvorli reviewed Jan 13, 2026

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am11 added 4 commits January 13, 2026 23:43

Address fb

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c1146d4

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

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Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

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jkotas reviewed Jan 14, 2026

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am11 added 2 commits January 14, 2026 01:37

Move MXCSR reset from PreStubWorker to CallEHFilterFunclet

3cac3e0

Merge branch 'main' into feature/il_throw_PUSH_COOP_PINVOKE_FRAME

4309af3

Bring throw helpers to PUSH_COOP_PINVOKE_FRAME plan #123015

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Bring throw helpers to PUSH_COOP_PINVOKE_FRAME plan #123015

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am11 commented Jan 8, 2026

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