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Fix spurious BROKEN frame at top of Linux thread stacks in CPU Stacks viewer #2375

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Merged
brianrob merged 2 commits into from
Mar 11, 2026
Merged

Fix spurious BROKEN frame at top of Linux thread stacks in CPU Stacks viewer #2375

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Copilot Mar 9, 2026
f78a0a9
Fix spurious BROKEN frame at top of Linux thread stacks in CPU Stacks…
Copilot Mar 9, 2026
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19 changes: 18 additions & 1 deletion src/TraceEvent/TraceEventStacks.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -662,6 +662,17 @@ private bool ReasonableTopFrame(StackSourceCallStackIndex callStackIndex, Thread
return true;
}

// On Linux, threads start from libc's __clone3, __clone, or __libc_start_main.
// Match libc.so.6, libc.so, libc-2.31.so, etc.
string moduleFileName = moduleFile.Name;
if (string.Compare(moduleFileName, "libc", StringComparison.OrdinalIgnoreCase) == 0 ||
moduleFileName.StartsWith("libc.", StringComparison.OrdinalIgnoreCase) ||
moduleFileName.StartsWith("libc-", StringComparison.OrdinalIgnoreCase))
{
m_goodTopModuleIndex = moduleFileIndex;
return true;
}

// The special processes 4 (System) and 0 (Kernel) can stay in the kernel without being broken.
if (moduleFile.FilePath.EndsWith("ntoskrnl.exe", StringComparison.OrdinalIgnoreCase))
{
Expand Down Expand Up @@ -873,7 +884,13 @@ public StackSourceCallStackIndex GetCallStack(CallStackIndex callStackIndex, Sta
var bangIdx = frameName.IndexOf('!');
if (0 < bangIdx)
{
if (!(5 <= bangIdx && string.Compare(frameName, bangIdx - 5, "ntdll", 0, 5, StringComparison.OrdinalIgnoreCase) == 0))
// Allow ntdll (Windows) and libc (Linux: libc.so.6, libc-2.31.so, etc.) as valid thread roots.
bool isNtdll = 5 <= bangIdx && string.Compare(frameName, bangIdx - 5, "ntdll", 0, 5, StringComparison.OrdinalIgnoreCase) == 0;
// Match libc, libc.so, libc.so.6, libc-2.31.so, but not libcrypto etc.
bool isLibc = 4 <= bangIdx &&
string.Compare(frameName, 0, "libc", 0, 4, StringComparison.OrdinalIgnoreCase) == 0 &&
(bangIdx == 4 || frameName[4] == '.' || frameName[4] == '-');
if (!isNtdll && !isLibc)
{
var brokenFrame = m_Interner.FrameIntern("BROKEN", m_emptyModuleIdx);
callerIdx = m_Interner.CallStackIntern(brokenFrame, callerIdx);
Expand Down