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[NativeAOT] macOS/iOS: Emit simple compact unwinding information #88724

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merged 4 commits into from
Aug 3, 2023
Merged

[NativeAOT] macOS/iOS: Emit simple compact unwinding information #88724

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e9b1340
Generate compact unwind sequence for methods with frame and no saved …
filipnavara Jul 11, 2023
803f511
Store prolog length in LSDA data when compact unwinding is used
filipnavara Jul 11, 2023
53117e3
Remove prolog length, detect prologs from instruction stream
filipnavara Aug 2, 2023
5446ab0
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filipnavara Aug 3, 2023
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112 changes: 101 additions & 11 deletions src/coreclr/nativeaot/Runtime/unix/UnixNativeCodeManager.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,8 @@ bool UnixNativeCodeManager::VirtualUnwind(MethodInfo* pMethodInfo, REGDISPLAY* p
{
UnixNativeMethodInfo * pNativeMethodInfo = (UnixNativeMethodInfo *)pMethodInfo;

return UnwindHelpers::StepFrame(pRegisterSet, pNativeMethodInfo->start_ip, pNativeMethodInfo->format, pNativeMethodInfo->unwind_info);
return UnwindHelpers::StepFrame(
pRegisterSet, pNativeMethodInfo->start_ip, pNativeMethodInfo->format, pNativeMethodInfo->unwind_info);
}

bool UnixNativeCodeManager::FindMethodInfo(PTR_VOID ControlPC,
Expand Down Expand Up @@ -258,14 +259,14 @@ uintptr_t UnixNativeCodeManager::GetConservativeUpperBoundForOutgoingArgs(Method

uint8_t unwindBlockFlags = *p++;

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) != 0)
p += sizeof(int32_t);

if ((unwindBlockFlags & UBF_FUNC_REVERSE_PINVOKE) != 0)
{
// Reverse PInvoke transition should be on the main function body only
assert(pNativeMethodInfo->pMainLSDA == pNativeMethodInfo->pLSDA);

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) != 0)
p += sizeof(int32_t);

if ((unwindBlockFlags & UBF_FUNC_HAS_EHINFO) != 0)
p += sizeof(int32_t);

Expand Down Expand Up @@ -320,14 +321,14 @@ bool UnixNativeCodeManager::UnwindStackFrame(MethodInfo * pMethodInfo,

uint8_t unwindBlockFlags = *p++;

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) != 0)
p += sizeof(int32_t);

if ((unwindBlockFlags & UBF_FUNC_REVERSE_PINVOKE) != 0)
{
// Reverse PInvoke transition should be on the main function body only
assert(pNativeMethodInfo->pMainLSDA == pNativeMethodInfo->pLSDA);

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) != 0)
p += sizeof(int32_t);

if ((unwindBlockFlags & UBF_FUNC_HAS_EHINFO) != 0)
p += sizeof(int32_t);

Expand Down Expand Up @@ -377,7 +378,78 @@ bool UnixNativeCodeManager::IsUnwindable(PTR_VOID pvAddress)
#endif

// VirtualUnwind can't unwind epilogues.
return TrailingEpilogueInstructionsCount(pMethodInfo, pvAddress) == 0;
return TrailingEpilogueInstructionsCount(pMethodInfo, pvAddress) == 0 && IsInProlog(pMethodInfo, pvAddress) != 1;
}

// checks for known prolog instructions generated by ILC and returns
// 1 - in prolog
// 0 - not in prolog,
// -1 - unknown.
int UnixNativeCodeManager::IsInProlog(MethodInfo * pMethodInfo, PTR_VOID pvAddress)
{
#if defined(TARGET_ARM64)

// post/pre


// stp with signed offset
// x010 1001 00xx xxxx xxxx xxxx xxxx xxxx
#define STP_BITS1 0x29000000
#define STP_MASK1 0x7FC00000

// stp with pre/post/no offset
// x010 100x x0xx xxxx xxxx xxxx xxxx xxxx
#define STP_BITS2 0x28000000
#define STP_MASK2 0x7E400000

// add fp, sp, x
// mov fp, sp
// 1001 0001 0xxx xxxx xxxx xx11 1111 1101
#define ADD_FP_SP_BITS 0x910003FD
#define ADD_FP_SP_MASK 0xFF8003FF

#define STP_RT2_RT_MASK 0x7C1F
#define STP_RT2_RT_FP_LR 0x781D
#define STP_RN_MASK 0x3E0
#define STP_RN_SP 0x3E0
#define STP_RN_FP 0x3A0


UnixNativeMethodInfo * pNativeMethodInfo = (UnixNativeMethodInfo *)pMethodInfo;
ASSERT(pNativeMethodInfo != NULL);

uint32_t* start = (uint32_t*)pNativeMethodInfo->pMethodStartAddress;
bool savedFpLr = false;
bool establishedFp = false;

for (uint32_t* pInstr = (uint32_t*)start; pInstr < pvAddress && !(savedFpLr && establishedFp); pInstr++)
{
uint32_t instr = *pInstr;

if (((instr & STP_MASK1) == STP_BITS1 || (instr & STP_MASK2) == STP_BITS2) &&
((instr & STP_RN_MASK) == STP_RN_SP || (instr & STP_RN_MASK) == STP_RN_FP))
{
// SP/FP-relative store of pair of registers
savedFpLr |= (instr & STP_RT2_RT_MASK) == STP_RT2_RT_FP_LR;
}
else if ((instr & ADD_FP_SP_MASK) == ADD_FP_SP_BITS)
{
establishedFp = true;
}
else
{
// TODO: Detect saving non-paired register, stack pointer adjustments
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return -1;
}
}

return savedFpLr && establishedFp ? 0 : 1;

#else

return -1;

#endif
}

// when stopped in an epilogue, returns the count of remaining stack-consuming instructions
Expand Down Expand Up @@ -682,9 +754,6 @@ bool UnixNativeCodeManager::GetReturnAddressHijackInfo(MethodInfo * pMethodIn

uint8_t unwindBlockFlags = *p++;

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) != 0)
p += sizeof(int32_t);

// Check whether this is a funclet
if ((unwindBlockFlags & UBF_FUNC_KIND_MASK) != UBF_FUNC_KIND_ROOT)
return false;
Expand All @@ -694,6 +763,9 @@ bool UnixNativeCodeManager::GetReturnAddressHijackInfo(MethodInfo * pMethodIn
if ((unwindBlockFlags & UBF_FUNC_REVERSE_PINVOKE) != 0)
return false;

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) != 0)
p += sizeof(int32_t);

if ((unwindBlockFlags & UBF_FUNC_HAS_EHINFO) != 0)
p += sizeof(int32_t);

Expand All @@ -718,6 +790,20 @@ bool UnixNativeCodeManager::GetReturnAddressHijackInfo(MethodInfo * pMethodIn
return true;
}

#if defined(TARGET_APPLE) && defined(TARGET_ARM64)
// If we are inside a prolog without a saved frame then we cannot safely unwind.
//
// Some known frame layouts use compact unwind encoding which cannot handle unwinding
// inside prolog or epilog, so don't even try that. These known sequences must be
// recognized by IsInProlog. Any other instruction sequence, known or unknown, falls
// through to the platform unwinder which should have DWARF information about the
// frame.
if (IsInProlog(pMethodInfo, (PTR_VOID)pRegisterSet->IP) == 1)
{
return false;
}
#endif

ASSERT(IsUnwindable((PTR_VOID)pRegisterSet->IP));

// Unwind the current method context to the caller's context to get its stack pointer
Expand Down Expand Up @@ -919,6 +1005,10 @@ PTR_VOID UnixNativeCodeManager::GetAssociatedData(PTR_VOID ControlPC)
PTR_UInt8 p = methodInfo.pLSDA;

uint8_t unwindBlockFlags = *p++;

if ((unwindBlockFlags & UBF_FUNC_KIND_MASK) != UBF_FUNC_KIND_ROOT)
p += sizeof(uint32_t);

if ((unwindBlockFlags & UBF_FUNC_HAS_ASSOCIATED_DATA) == 0)
return NULL;

Expand Down
2 changes: 2 additions & 0 deletions src/coreclr/nativeaot/Runtime/unix/UnixNativeCodeManager.h
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,8 @@ class UnixNativeCodeManager : public ICodeManager

bool IsUnwindable(PTR_VOID pvAddress);

int IsInProlog(MethodInfo * pMethodInfo, PTR_VOID pvAddress);

int TrailingEpilogueInstructionsCount(MethodInfo * pMethodInfo, PTR_VOID pvAddress);

bool GetReturnAddressHijackInfo(MethodInfo * pMethodInfo,
Expand Down
75 changes: 63 additions & 12 deletions src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ObjectWriter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,8 @@ public class ObjectWriter : IDisposable, ITypesDebugInfoWriter
private HashSet<int> _offsetToCfiStart = new HashSet<int>();
// Code offsets that ends a frame
private HashSet<int> _offsetToCfiEnd = new HashSet<int>();
// Code offsets to compact unwind encoding
private Dictionary<int, uint> _offsetToCfiCompactEncoding = new Dictionary<int, uint>();
// Used to assert whether frames are not overlapped.
private bool _frameOpened;

Expand Down Expand Up @@ -248,6 +250,14 @@ public void EmitCFICode(int nativeOffset, byte[] blob)
EmitCFICode(_nativeObjectWriter, nativeOffset, blob);
}

[DllImport(NativeObjectWriterFileName)]
private static extern void EmitCFICompactUnwindEncoding(IntPtr objWriter, uint encoding);
public void EmitCFICompactUnwindEncoding(uint encoding)
{
Debug.Assert(_frameOpened);
EmitCFICompactUnwindEncoding(_nativeObjectWriter, encoding);
}

[DllImport(NativeObjectWriterFileName)]
private static extern void EmitDebugFileInfo(IntPtr objWriter, int fileId, string fileName);
public void EmitDebugFileInfo(int fileId, string fileName)
Expand Down Expand Up @@ -574,12 +584,36 @@ public void PublishUnwindInfo(ObjectNode node)
}
}

private static ReadOnlySpan<byte> DwarfArm64EmptyFrame => new byte[]
{
0x04, 0x00, 0xFF, 0xFF, 0x10, 0x00, 0x00, 0x00,
0x04, 0x02, 0x1D, 0x00, 0x00, 0x00, 0x00, 0x00,
0x04, 0x02, 0x1E, 0x00, 0x08, 0x00, 0x00, 0x00,
0x08, 0x01, 0x1D, 0x00, 0x00, 0x00, 0x00, 0x00
};
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private bool TryGetCompactUnwindEncoding(byte[] blob, out uint encoding)
{
if (_targetPlatform.Architecture == TargetArchitecture.ARM64)
{
if (blob.AsSpan().SequenceEqual(DwarfArm64EmptyFrame))
{
// Frame-based encoding, no saved registers
encoding = 0x04000000;
return true;
}
}
encoding = 0;
return false;
}

public void BuildCFIMap(NodeFactory factory, ObjectNode node)
{
_offsetToCfis.Clear();
_offsetToCfiStart.Clear();
_offsetToCfiEnd.Clear();
_offsetToCfiLsdaBlobName.Clear();
_offsetToCfiCompactEncoding.Clear();
_frameOpened = false;

INodeWithCodeInfo nodeWithCodeInfo = node as INodeWithCodeInfo;
Expand Down Expand Up @@ -609,6 +643,7 @@ public void BuildCFIMap(NodeFactory factory, ObjectNode node)
int end = frameInfo.EndOffset;
int len = frameInfo.BlobData.Length;
byte[] blob = frameInfo.BlobData;
bool emitDwarf = true;

ObjectNodeSection lsdaSection = LsdaSection;
if (ShouldShareSymbol(node))
Expand All @@ -621,6 +656,13 @@ public void BuildCFIMap(NodeFactory factory, ObjectNode node)
byte[] blobSymbolName = _sb.ToUtf8String().UnderlyingArray;
EmitSymbolDef(blobSymbolName);

if (_targetPlatform.IsOSXLike &&
TryGetCompactUnwindEncoding(blob, out uint compactEncoding))
{
_offsetToCfiCompactEncoding[start] = compactEncoding;
emitDwarf = false;
}

FrameInfoFlags flags = frameInfo.Flags;
flags |= ehInfo != null ? FrameInfoFlags.HasEHInfo : 0;
flags |= associatedDataNode != null ? FrameInfoFlags.HasAssociatedData : 0;
Expand Down Expand Up @@ -662,21 +704,25 @@ public void BuildCFIMap(NodeFactory factory, ObjectNode node)
_byteInterruptionOffsets[start] = true;
_byteInterruptionOffsets[end] = true;
_offsetToCfiLsdaBlobName.Add(start, blobSymbolName);
for (int j = 0; j < len; j += CfiCodeSize)

if (emitDwarf)
{
// The first byte of CFI_CODE is offset from the range the frame covers.
// Compute code offset from the root method.
int codeOffset = blob[j] + start;
List<byte[]> cfis;
if (!_offsetToCfis.TryGetValue(codeOffset, out cfis))
for (int j = 0; j < len; j += CfiCodeSize)
{
cfis = new List<byte[]>();
_offsetToCfis.Add(codeOffset, cfis);
_byteInterruptionOffsets[codeOffset] = true;
// The first byte of CFI_CODE is offset from the range the frame covers.
// Compute code offset from the root method.
int codeOffset = blob[j] + start;
List<byte[]> cfis;
if (!_offsetToCfis.TryGetValue(codeOffset, out cfis))
{
cfis = new List<byte[]>();
_offsetToCfis.Add(codeOffset, cfis);
_byteInterruptionOffsets[codeOffset] = true;
}
byte[] cfi = new byte[CfiCodeSize];
Array.Copy(blob, j, cfi, 0, CfiCodeSize);
cfis.Add(cfi);
}
byte[] cfi = new byte[CfiCodeSize];
Array.Copy(blob, j, cfi, 0, CfiCodeSize);
cfis.Add(cfi);
}
}

Expand Down Expand Up @@ -726,6 +772,11 @@ public void EmitCFICodes(int offset)
// prefix to `_fram`.
"_fram"u8.CopyTo(blobSymbolName);
EmitSymbolDef(blobSymbolName);

if (_offsetToCfiCompactEncoding.TryGetValue(offset, out uint compactEncoding))
{
EmitCFICompactUnwindEncoding(compactEncoding);
}
}
}

Expand Down
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