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Improve stack overflow stack trace pretty print #122243

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Improve stack overflow stacktrace pretty print
janvorli Dec 5, 2025
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janvorli Dec 5, 2025
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107 changes: 65 additions & 42 deletions src/coreclr/vm/eepolicy.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -162,13 +162,6 @@ class CallStackLogger
// MethodDescs of the stack frames, the TOS is at index 0
CDynArray<MethodDesc*> m_frames;

// Index of a stack frame where a possible repetition of frames starts
int m_commonStartIndex = -1;
// Length of the largest found repeated sequence of frames
int m_largestCommonStartLength = 0;
// Number of repetitions of the largest repeated sequence of frames
int m_largestCommonStartRepeat = 0;

StackWalkAction LogCallstackForLogCallbackWorker(CrawlFrame *pCF)
{
WRAPPER_NO_CONTRACT;
Expand All @@ -183,44 +176,14 @@ class CallStackLogger
}
}

MethodDesc *pMD = pCF->GetFunction();

if (m_commonStartIndex != -1)
{
// Some common frames were already found

if (m_frames[m_frames.Count() - m_commonStartIndex] != pMD)
{
// The frame being added is not part of the repeated sequence
if (m_frames.Count() / m_commonStartIndex >= 2)
{
// A sequence repeated at least twice was found. It is the largest one that was found so far
m_largestCommonStartLength = m_commonStartIndex;
m_largestCommonStartRepeat = m_frames.Count() / m_commonStartIndex;
}

m_commonStartIndex = -1;
}
}

if (m_commonStartIndex == -1)
{
if ((m_frames.Count() != 0) && (pMD == m_frames[0]))
{
// We have found a frame with the same MethodDesc as the frame at the top of the stack,
// possibly a new repeated sequence is starting.
m_commonStartIndex = m_frames.Count();
}
}

MethodDesc** itemPtr = m_frames.Append();
if (itemPtr == nullptr)
{
// Memory allocation failure
return SWA_ABORT;
}

*itemPtr = pMD;
*itemPtr = pCF->GetFunction();

return SWA_CONTINUE;
}
Expand Down Expand Up @@ -260,22 +223,82 @@ class CallStackLogger
{
WRAPPER_NO_CONTRACT;

if (m_largestCommonStartLength != 0)
// Length of the largest found repeated sequence of frames
int largestCommonLength = 0;
// Number of repetitions of the largest repeated sequence of frames
int largestCommonRepeat = 0;

// Start index of the repetition
int largestCommonStartOffset;
for (largestCommonStartOffset = 0; largestCommonStartOffset < m_frames.Count(); largestCommonStartOffset++)
{
// Index of a stack frame where a possible repetition of frames starts
int commonStartIndex = -1;
largestCommonLength = 0;
largestCommonRepeat = 0;

for (int i = largestCommonStartOffset; i < m_frames.Count(); i++)
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@jkotas jkotas Dec 6, 2025

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This looks like a quadratic algorithm. What's the worst-case delay that it can lead to in real-world apps?

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@jkotas jkotas Dec 6, 2025

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I believe there are O(N log N) algorithms to do this if this one is too slow.

{
MethodDesc* pMD = m_frames[i];
if (commonStartIndex != -1)
{
// Some common frames were already found

int commonLength = commonStartIndex - largestCommonStartOffset;
if (m_frames[i - commonLength] != pMD)
{
// The frame being added is not part of the repeated sequence
int commonRepeat = (i - largestCommonStartOffset) / commonLength;
if (commonRepeat >= 2)
{
// A sequence repeated at least twice was found. It is the largest one that was found so far
largestCommonLength = commonLength;
largestCommonRepeat = commonRepeat;
}

commonStartIndex = -1;
}
}

if (commonStartIndex == -1)
{
if ((i != largestCommonStartOffset) && (pMD == m_frames[largestCommonStartOffset]))
{
// We have found a frame with the same MethodDesc as the frame at the start of the repetition search (index largestCommonStartOffset),
// possibly a new repeated sequence is starting.
commonStartIndex = i;
}
}
}

if (largestCommonRepeat != 0)
{
// A repeated sequence of frames was identified
break;
}
}

for (int i = 0; i < largestCommonStartOffset; i++)
{
PrintFrame(i, pWordAt);
}

if (largestCommonLength != 0)
{
SmallStackSString repeatStr;
repeatStr.AppendPrintf("Repeated %d times:\n", m_largestCommonStartRepeat);
repeatStr.AppendPrintf("Repeated %d times:\n", largestCommonRepeat);

PrintToStdErrW(repeatStr.GetUnicode());

PrintToStdErrA("--------------------------------\n");
for (int i = 0; i < m_largestCommonStartLength; i++)
for (int i = largestCommonStartOffset; i < largestCommonStartOffset + largestCommonLength; i++)
{
PrintFrame(i, pWordAt);
}
PrintToStdErrA("--------------------------------\n");
}

for (int i = m_largestCommonStartLength * m_largestCommonStartRepeat; i < m_frames.Count(); i++)
for (int i = largestCommonLength * largestCommonRepeat + largestCommonStartOffset; i < m_frames.Count(); i++)
{
PrintFrame(i, pWordAt);
}
Expand Down
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