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Fix RISC-V unwind scope calculations #132229

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Merged
rcj1 merged 5 commits into from
Aug 13, 2026
Merged

Fix RISC-V unwind scope calculations #132229

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2e45525
Fix RISC-V unwind scope calculations
rcj1 Aug 11, 2026
0850eeb
Merge RISC-V unwind scope fix
Copilot Aug 12, 2026
02a3393
Add RISC-V epilog unwind regression test
Copilot Aug 12, 2026
a689e14
Clarify RISCV64 unwind scope comment units
Copilot Aug 12, 2026
3a8e949
Merge remote-tracking branch 'rachel' into copilot/risc-v-audit-add-u…
rcj1 Aug 13, 2026
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44 changes: 24 additions & 20 deletions ...stics.DataContractReader.Contracts/Contracts/StackWalk/Context/RISCV64/RISCV64Unwinder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -132,7 +132,7 @@ private bool VirtualUnwindFull(
}

uint functionLength = headerWord & 0x3ffffu;
uint offsetInFunction = (controlPcRva - functionEntry.BeginAddress) / 4;
uint offsetInFunction = (controlPcRva - functionEntry.BeginAddress) / 2;

//
// Determine the number of epilog scope records and the maximum number
Expand Down Expand Up @@ -167,7 +167,7 @@ private bool VirtualUnwindFull(

TargetPointer unwindCodePtr = unwindDataPtr + 4 * epilogScopeCount;
TargetPointer unwindCodesEndPtr = unwindCodePtr + 4 * unwindWords;
uint skipWords = 0;
uint skipHalfwords = 0;

//
// If we're near the start of the function, and this function has a prolog,
Expand All @@ -176,24 +176,25 @@ private bool VirtualUnwindFull(
// need to skip some to account for partial execution of the prolog.
//
// N.B. As an optimization here, note that each byte of unwind codes can
// describe at most one 32-bit instruction. Thus, the largest prologue
// that could possibly be described by UnwindWords (which is 4 * the
// number of unwind code bytes) is 4 * UnwindWords words. If
// OffsetInFunction is larger than this value, it is guaranteed to be
// in the body of the function.
// describe at most one instruction, and each instruction can cover at
// most two halfwords. Thus, the largest prolog that could possibly be
// described by UnwindWords (which is 4 * the number of unwind code
// bytes) is 2 * (4 * UnwindWords) halfwords. If OffsetInFunction is
// larger than this value, it is guaranteed to be in the body of the
// function.
//
uint scopeSize;
if (offsetInFunction < 4 * unwindWords)
if (offsetInFunction < 2 * (4 * unwindWords))
{
scopeSize = ComputeScopeSize(unwindCodePtr, unwindCodesEndPtr);
scopeSize = 2 * ComputeScopeSize(unwindCodePtr, unwindCodesEndPtr, isEpilog: false);
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if (offsetInFunction < scopeSize)
{
skipWords = scopeSize - offsetInFunction;
skipHalfwords = scopeSize - offsetInFunction;
}
}

if (skipWords > 0)
if (skipHalfwords > 0)
{
// Found that we are in the middle of a prolog, no need to check for epilog scopes
}
Expand All @@ -215,9 +216,9 @@ private bool VirtualUnwindFull(
//
else if ((headerWord & (1 << 21)) != 0)
{
if (offsetInFunction + (4 * unwindWords - unwindIndex) >= functionLength)
if (offsetInFunction + 2 * (4 * unwindWords - unwindIndex) >= functionLength)
{
scopeSize = ComputeScopeSize(unwindCodePtr + unwindIndex, unwindCodesEndPtr);
scopeSize = 2 * ComputeScopeSize(unwindCodePtr + unwindIndex, unwindCodesEndPtr, isEpilog: true);
uint scopeStart = functionLength - scopeSize;

//
Expand All @@ -227,7 +228,7 @@ private bool VirtualUnwindFull(
if (offsetInFunction >= scopeStart)
{
unwindCodePtr += unwindIndex;
skipWords = offsetInFunction - scopeStart;
skipHalfwords = offsetInFunction - scopeStart;
}
}
}
Expand All @@ -254,14 +255,14 @@ private bool VirtualUnwindFull(
break;

unwindIndex = headerWord >> 22;
if (offsetInFunction < scopeStart + (4 * unwindWords - unwindIndex))
if (offsetInFunction < scopeStart + 2 * (4 * unwindWords - unwindIndex))
{
scopeSize = ComputeScopeSize(unwindCodePtr + unwindIndex, unwindCodesEndPtr);
scopeSize = 2 * ComputeScopeSize(unwindCodePtr + unwindIndex, unwindCodesEndPtr, isEpilog: true);

if (offsetInFunction < scopeStart + scopeSize)
{
unwindCodePtr += unwindIndex;
skipWords = offsetInFunction - scopeStart;
skipHalfwords = offsetInFunction - scopeStart;
break;
}
}
Expand All @@ -273,15 +274,15 @@ private bool VirtualUnwindFull(
// to skip.
//

while (unwindCodePtr < unwindCodesEndPtr && skipWords > 0)
while (unwindCodePtr < unwindCodesEndPtr && skipHalfwords > 0)
{
byte curCode = _target.Read<byte>(unwindCodePtr);
if (OpcodeIsEnd(curCode))
{
break;
}
unwindCodePtr += UnwindCodeSizeTable[curCode];
skipWords--;
skipHalfwords -= 2;
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}

//
Expand Down Expand Up @@ -318,7 +319,7 @@ private bool VirtualUnwindFull(
return true;
}

private uint ComputeScopeSize(TargetPointer unwindCodePtr, TargetPointer unwindCodesEndPtr)
private uint ComputeScopeSize(TargetPointer unwindCodePtr, TargetPointer unwindCodesEndPtr, bool isEpilog)
{
//
// Iterate through the unwind codes until we hit an end marker.
Expand All @@ -338,6 +339,9 @@ private uint ComputeScopeSize(TargetPointer unwindCodePtr, TargetPointer unwindC
scopeSize++;
}

if (isEpilog)
scopeSize++;

return scopeSize;
}

Expand Down
70 changes: 70 additions & 0 deletions src/native/managed/cdac/tests/UnitTests/StackWalkTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,76 @@ public void ARMUnwind_CompactEpilog_RestoresCallerContext()
Assert.NotEqual(0u, context.ContextFlags & (uint)ARMContext.ContextFlagsValues.CONTEXT_UNWOUND_TO_CALL);
}

[Fact]
public void RISCV64Unwind_SingleEpilogAtReturn_DoesNotReapplyStackAdjustment()
{
MockTarget.Architecture arch = new() { IsLittleEndian = true, Is64Bit = true };
TestPlaceholderTarget.Builder targetBuilder = new(arch);
TargetTestHelpers helpers = targetBuilder.MemoryBuilder.TargetTestHelpers;

const uint ImageBase = 0x1000_0000;
const uint FunctionStart = 0x1000;
const uint RuntimeFunctionAddress = 0x1800;
const uint UnwindDataRva = 0x2000;
const ulong CurrentSp = 0x3000;
const ulong ReturnAddress = 0x1234_5678_9abc_def0;

Layout<MockRuntimeFunction> runtimeFunctionLayout = MockRuntimeFunction.CreateLayout(arch, includeEndAddress: false);
byte[] runtimeFunctionData = new byte[runtimeFunctionLayout.Size];
MockRuntimeFunction runtimeFunction = runtimeFunctionLayout.Create(runtimeFunctionData, RuntimeFunctionAddress);
runtimeFunction.BeginAddress = FunctionStart;
runtimeFunction.UnwindData = UnwindDataRva;
targetBuilder.MemoryBuilder.AddHeapFragment(new MockMemorySpace.HeapFragment
{
Address = RuntimeFunctionAddress,
Data = runtimeFunctionData,
Name = "Runtime function",
});

byte[] unwindData = new byte[2 * sizeof(uint)];
uint unwindHeader =
8u | // FunctionLength = 8 halfwords
(1u << 21) | // E = 1: single epilog at the end of the function
(1u << 27); // CodeWords = 1
helpers.Write(unwindData.AsSpan(0, sizeof(uint)), unwindHeader);
unwindData[sizeof(uint)] = 0x01; // alloc_s 1: restore 16 bytes of stack
unwindData[sizeof(uint) + 1] = 0xe4; // end
targetBuilder.MemoryBuilder.AddHeapFragment(new MockMemorySpace.HeapFragment
{
Address = ImageBase + UnwindDataRva,
Data = unwindData,
Name = "Unwind data",
});

TargetCodePointer controlPc = new(ImageBase + FunctionStart + 12);
CodeBlockHandle codeBlock = new(new TargetPointer(controlPc.Value));
Mock<IExecutionManager> executionManager = new();
executionManager.Setup(e => e.GetCodeBlockHandle(controlPc)).Returns(codeBlock);
executionManager.Setup(e => e.GetUnwindInfoBaseAddress(codeBlock)).Returns(new TargetPointer(ImageBase));
executionManager.Setup(e => e.GetUnwindInfo(codeBlock)).Returns(new TargetPointer(RuntimeFunctionAddress));

TestPlaceholderTarget target = targetBuilder
.AddTypes(new Dictionary<DataType, Target.TypeInfo>
{
[DataType.RuntimeFunction] = TargetTestHelpers.CreateTypeInfo(runtimeFunctionLayout),
})
.AddMockContract(executionManager.Object)
.Build();

RISCV64Context context = new()
{
ContextFlags = (uint)RISCV64Context.ContextFlagsValues.CONTEXT_FULL,
Sp = CurrentSp,
Ra = ReturnAddress,
Pc = controlPc.Value,
};

Assert.True(new Contracts.StackWalkHelpers.RISCV64.RISCV64Unwinder(target).Unwind(ref context));
Assert.Equal(CurrentSp, context.Sp);
Assert.Equal(ReturnAddress, context.Pc);
Assert.NotEqual(0u, context.ContextFlags & (uint)RISCV64Context.ContextFlagsValues.CONTEXT_UNWOUND_TO_CALL);
}

[Fact]
public void ARM64Unwind_SaveAnyPair_RestoresCallerContext()
{
Expand Down