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Merged
Jarred-Sumner merged 17 commits into from
Apr 14, 2026
+378 −290
Merged

cpu-prof: match Node/Deno Chrome DevTools format #29241

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5cdb657
cpu-prof: match Node/Deno Chrome DevTools format
robobun Apr 13, 2026
0e9c177
[autofix.ci] apply automated fixes
autofix-ci[bot] Apr 13, 2026
57bf345
cpu-prof: carry the def-mapped URL through, tighten positionTicks test
robobun Apr 13, 2026
36ee468
cpu-prof test: assert sum(positionTicks) <= hitCount in sourcemap pat…
robobun Apr 13, 2026
97bfb9e
cpu-prof test: trim top-of-file prose, bump per-test timeout to 30s
robobun Apr 13, 2026
50db0ef
[autofix.ci] apply automated fixes
autofix-ci[bot] Apr 13, 2026
e840181
cpu-prof: delete dead stopCPUProfilerAndGetJSON
robobun Apr 13, 2026
a1756db
cpu-prof test: gate on isDebug so release CI lanes skip
robobun Apr 13, 2026
fab5f13
ci: retrigger after darwin-13-aarch64 runner flake
robobun Apr 13, 2026
a9c4af2
cpu-prof test: revert skipIf(!isDebug), let release lanes run
robobun Apr 13, 2026
a811a82
cpu-prof test: drop explicit timeout override
robobun Apr 13, 2026
09dfc0c
[autofix.ci] apply automated fixes
autofix-ci[bot] Apr 13, 2026
2bc31ad
cpu-prof: drop sample line when source maps to a different file
robobun Apr 13, 2026
538c046
cpu-prof: normalize callFrame.url to file:// after sourcemap calls
robobun Apr 13, 2026
68bac11
cpu-prof test: rename unused stderr → _stderr, fix stale comment
robobun Apr 13, 2026
a60bbbe
cpu-prof: fix misleading sampleURL comment + tighten fib merge key
robobun Apr 13, 2026
8633b6c
ci: retrigger gate after staging webkit caches
robobun Apr 13, 2026
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193 changes: 169 additions & 24 deletions src/bun.js/bindings/BunCPUProfiler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
#include <wtf/HashSet.h>
#include <wtf/URL.h>
#include <algorithm>
#include <limits>

extern "C" void Bun__startCPUProfiler(JSC::VM* vm);
extern "C" void Bun__stopCPUProfiler(JSC::VM* vm, BunString* outJSON, BunString* outText);
Expand Down Expand Up @@ -66,10 +67,19 @@ struct ProfileNode {
WTF::String functionName;
WTF::String url;
int scriptId;
// lineNumber/columnNumber are the location where the function is DEFINED
// (matching Node/Deno/Chrome DevTools), stored as 0-indexed values ready
// for JSON emission. -1 means "unknown".
int lineNumber;
int columnNumber;
int hitCount;
WTF::Vector<int> children;
// Per-line sample counts for this node, keyed by 1-indexed source line.
// Emitted as `positionTicks` in the JSON output when non-empty, matching
// the Chrome DevTools CPU profile format used by Node and Deno.
// Lines are guaranteed non-zero, so the default IntHashTraits (which reserve
// 0 and -1 as empty/deleted sentinels) are safe here.
WTF::HashMap<int, int, WTF::IntHash<int>> positionTicks;
};

Comment on lines +77 to 84
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@claude claude bot Apr 13, 2026

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🟡 The comment on positionTicks in the ProfileNode struct cites incorrect sentinel values: it says the default IntHashTraits reserves 0 and -1, but WTF::HashTraits<int> (the actual key traits) uses 0 as the empty sentinel and std::numeric_limits<int>::max() (INT_MAX) as the deleted sentinel — not -1. The code is functionally correct since source line numbers are always small positive integers that can never equal INT_MAX, but the comment misstates the reserved values and names a nonexistent WTF type.

Extended reasoning...

The comment at lines 80-81 reads: "the default IntHashTraits (which reserve 0 and -1 as empty/deleted sentinels) are safe here." This has two inaccuracies.

First, "IntHashTraits" is not a WTF type name. The HashMap declaration is WTF::HashMap<int, int, WTF::IntHash<int>>, where WTF::IntHash<int> is the hash function and the key traits default to WTF::HashTraits<int>. The comment conflates the hash function name with the traits type name.

Second, the sentinel values cited (-1 as deleted) are likely wrong. Modern WebKit WTF defines HashTraits<int> via IntegralHashTraits<int>, which sets the empty sentinel to T() (0) via emptyValueIsZero = true, and the deleted sentinel to std::numeric_limits<T>::max() (INT_MAX for int). The comment's claim of -1 as the deleted sentinel does not match this type.

One refuting verifier argued that GenericHashTraits<T> for signed integer types uses T(-1) as the deleted sentinel, making the comment correct. However, multiple confirming verifiers independently traced the trait hierarchy to IntegralHashTraits<int> with INT_MAX as the deleted value. Regardless of which exact sentinel value is used, the type name "IntHashTraits" is not a real WTF type and will mislead any reader who tries to look it up.

The runtime impact is zero: sampleLine is always a 1-indexed source line number populated only when sourceMappedLineColumn.line > 0, making it a small positive integer that cannot collide with 0, -1, INT_MAX, or INT_MAX-1. The safety invariant holds regardless of which sentinel values WTF actually uses.

The risk of the misleading comment is that a future developer might: (a) add a spurious sampleLine != -1 guard believing -1 is a sentinel; (b) rely on the sampleLine > 0 guard as sufficient protection against the alleged "0 sentinel" while missing the actual INT_MAX sentinel; or (c) spend time searching for the nonexistent "IntHashTraits" type. The fix is to replace the comment with the correct type name (WTF::HashTraits<int>) and accurate sentinel values, along with the real safety justification: source line numbers are small positive integers, nowhere near INT_MAX.

WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)
Expand Down Expand Up @@ -160,8 +170,13 @@ WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)
WTF::String functionName;
WTF::String url;
int scriptId = 0;
int lineNumber = -1;
int columnNumber = -1;
// Function-definition line/column (0-indexed for JSON emit, matching
// Node/Deno/Chrome DevTools). -1 means "unknown".
int functionDefLine = -1;
int functionDefColumn = -1;
// Current-sample line (1-indexed) — fed to positionTicks when this
// frame is the top of the stack. 0 means "unknown".
int sampleLine = 0;

// Get function name - displayName works for all frame types
functionName = frame.displayName(vm);
Expand Down Expand Up @@ -200,24 +215,67 @@ WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)
}
}

// Function definition location. JSC returns these 1-based;
// Node/Deno/Chrome DevTools emit them 0-based in the JSON.
// We remap this (not the sample position) through the
// sourcemap callback so callFrame.url/line/column all agree
// on the function's DEFINITION site — bundled/transpiled
// scripts then report the original source for the node while
// positionTicks reports original-source sample lines.
int rawFunctionStartLine = frame.functionStartLine();
unsigned rawFunctionStartColumn = frame.functionStartColumn();
if (rawFunctionStartLine > 0 && rawFunctionStartColumn != std::numeric_limits<unsigned>::max()) {
JSC::LineColumn functionStartLineColumn {
static_cast<unsigned>(rawFunctionStartLine),
rawFunctionStartColumn,
};
if (provider) {
#if USE(BUN_JSC_ADDITIONS)
auto& fn = vm.computeLineColumnWithSourcemap();
if (fn) {
// `url` is the out-param — on a successful remap
// it becomes the original-source URL, matching
// the line/column we're emitting.
fn(vm, provider, functionStartLineColumn, url);
}
#endif
}
// Emit 0-indexed, clamping at 0 so we never underflow.
functionDefLine = functionStartLineColumn.line > 0
? static_cast<int>(functionStartLineColumn.line) - 1
: 0;
functionDefColumn = functionStartLineColumn.column > 0
? static_cast<int>(functionStartLineColumn.column) - 1
: 0;
}

if (frame.hasExpressionInfo()) {
// Apply sourcemap if available
// Current sample position (what line inside the function
// was executing). Apply sourcemap if available, but keep
// the URL we already resolved for the function definition
// — a throwaway out-param ensures the sample remap can't
// clobber `url` with the sample's source file (which, for
// inlined helpers, may differ from the function's).
JSC::LineColumn sourceMappedLineColumn = frame.semanticLocation.lineColumn;
if (provider) {
#if USE(BUN_JSC_ADDITIONS)
auto& fn = vm.computeLineColumnWithSourcemap();
if (fn) {
fn(vm, provider, sourceMappedLineColumn, url);
WTF::String scratchURL = url;
fn(vm, provider, sourceMappedLineColumn, scratchURL);
}
#endif
}
lineNumber = static_cast<int>(sourceMappedLineColumn.line);
columnNumber = static_cast<int>(sourceMappedLineColumn.column);
// positionTicks lines are 1-indexed in the Chrome format;
// semanticLocation.line is already 1-based.
if (sourceMappedLineColumn.line > 0)
sampleLine = static_cast<int>(sourceMappedLineColumn.line);
}
}

// Create a unique key for this frame based on parent + callFrame
// This creates separate nodes for the same function in different call paths
// Create a unique key for this frame based on parent + callFrame.
// line/column here identify the function's DEFINITION, so all samples
// of the same function under the same parent collapse to one node.
WTF::StringBuilder keyBuilder;
keyBuilder.append(currentParentId);
keyBuilder.append(':');
Expand All @@ -227,9 +285,9 @@ WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)
keyBuilder.append(':');
keyBuilder.append(scriptId);
keyBuilder.append(':');
keyBuilder.append(lineNumber);
keyBuilder.append(functionDefLine);
keyBuilder.append(':');
keyBuilder.append(columnNumber);
keyBuilder.append(functionDefColumn);

WTF::String key = keyBuilder.toString();

Expand All @@ -245,8 +303,8 @@ WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)
node.functionName = functionName;
node.url = url;
node.scriptId = scriptId;
node.lineNumber = lineNumber;
node.columnNumber = columnNumber;
node.lineNumber = functionDefLine;
node.columnNumber = functionDefColumn;
node.hitCount = 0;

nodes.append(WTF::move(node));
Expand All @@ -262,9 +320,13 @@ WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)

currentParentId = nodeId;

// If this is the top frame, increment hit count
// If this is the top frame, increment hit count and record the
// sample line in positionTicks (matching Node/Deno/Chrome DevTools).
if (i == 0) {
nodes[nodeId - 1].hitCount++;
if (sampleLine > 0) {
nodes[nodeId - 1].positionTicks.add(sampleLine, 0).iterator->value++;
}
}
}

Expand Down Expand Up @@ -313,6 +375,26 @@ WTF::String stopCPUProfilerAndGetJSON(JSC::VM& vm)
nodeObj->setValue("children"_s, childrenArray);
}

// Per-line sample counts (Chrome DevTools format). Emit sorted by line
// for deterministic output.
if (!node.positionTicks.isEmpty()) {
WTF::Vector<std::pair<int, int>> sortedTicks;
sortedTicks.reserveInitialCapacity(node.positionTicks.size());
for (auto& entry : node.positionTicks)
sortedTicks.append({ entry.key, entry.value });
std::sort(sortedTicks.begin(), sortedTicks.end(), [](const auto& a, const auto& b) {
return a.first < b.first;
});
auto positionTicksArray = JSON::Array::create();
for (auto& [line, ticks] : sortedTicks) {
auto tickObj = JSON::Object::create();
tickObj->setInteger("line"_s, line);
tickObj->setInteger("ticks"_s, ticks);
positionTicksArray->pushValue(tickObj);
}
nodeObj->setValue("positionTicks"_s, positionTicksArray);
}

nodesArray->pushValue(nodeObj);
}
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Outdated
json->setValue("nodes"_s, nodesArray);
Expand Down Expand Up @@ -638,8 +720,11 @@ void stopCPUProfiler(JSC::VM& vm, WTF::String* outJSON, WTF::String* outText)
WTF::String functionName = frame.displayName(vm);
WTF::String url;
int scriptId = 0;
int lineNumber = -1;
int columnNumber = -1;
// Function-definition line/column (0-indexed) for callFrame.
int functionDefLine = -1;
int functionDefColumn = -1;
// Current-sample line (1-indexed) for positionTicks.
int sampleLine = 0;

if (frame.frameType == JSC::SamplingProfiler::FrameType::Executable && frame.executable) {
auto sourceProviderAndID = frame.sourceProviderAndID();
Expand All @@ -664,20 +749,57 @@ void stopCPUProfiler(JSC::VM& vm, WTF::String* outJSON, WTF::String* outText)
url = WTF::URL::fileURLWithFileSystemPath(url).string();
}

// Function definition location. JSC returns these 1-based;
// Node/Deno/Chrome DevTools emit them 0-based in the JSON.
// The definition (not the sample position) is remapped
// through the sourcemap callback so callFrame.url and
// callFrame.line/column agree on the function's source.
int rawFunctionStartLine = frame.functionStartLine();
unsigned rawFunctionStartColumn = frame.functionStartColumn();
if (rawFunctionStartLine > 0 && rawFunctionStartColumn != std::numeric_limits<unsigned>::max()) {
JSC::LineColumn functionStartLineColumn {
static_cast<unsigned>(rawFunctionStartLine),
rawFunctionStartColumn,
};
if (provider) {
#if USE(BUN_JSC_ADDITIONS)
auto& fn = vm.computeLineColumnWithSourcemap();
if (fn) {
// `url` is the out-param — on a successful
// remap it becomes the original-source URL.
fn(vm, provider, functionStartLineColumn, url);
}
#endif
}
functionDefLine = functionStartLineColumn.line > 0
? static_cast<int>(functionStartLineColumn.line) - 1
: 0;
functionDefColumn = functionStartLineColumn.column > 0
? static_cast<int>(functionStartLineColumn.column) - 1
: 0;
}
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if (frame.hasExpressionInfo()) {
// Sample position for positionTicks — a throwaway
// out-param ensures the sample remap can't clobber
// `url` with a different file than the definition.
JSC::LineColumn sourceMappedLineColumn = frame.semanticLocation.lineColumn;
if (provider) {
#if USE(BUN_JSC_ADDITIONS)
auto& fn = vm.computeLineColumnWithSourcemap();
if (fn)
fn(vm, provider, sourceMappedLineColumn, url);
if (fn) {
WTF::String scratchURL = url;
fn(vm, provider, sourceMappedLineColumn, scratchURL);
}
#endif
}
lineNumber = static_cast<int>(sourceMappedLineColumn.line);
columnNumber = static_cast<int>(sourceMappedLineColumn.column);
if (sourceMappedLineColumn.line > 0)
sampleLine = static_cast<int>(sourceMappedLineColumn.line);
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}
}

// line/column here identify the function's DEFINITION, so all
// samples of the same function under the same parent collapse.
WTF::StringBuilder keyBuilder;
keyBuilder.append(currentParentId);
keyBuilder.append(':');
Expand All @@ -687,9 +809,9 @@ void stopCPUProfiler(JSC::VM& vm, WTF::String* outJSON, WTF::String* outText)
keyBuilder.append(':');
keyBuilder.append(scriptId);
keyBuilder.append(':');
keyBuilder.append(lineNumber);
keyBuilder.append(functionDefLine);
keyBuilder.append(':');
keyBuilder.append(columnNumber);
keyBuilder.append(functionDefColumn);

WTF::String key = keyBuilder.toString();

Expand All @@ -704,8 +826,8 @@ void stopCPUProfiler(JSC::VM& vm, WTF::String* outJSON, WTF::String* outText)
node.functionName = functionName;
node.url = url;
node.scriptId = scriptId;
node.lineNumber = lineNumber;
node.columnNumber = columnNumber;
node.lineNumber = functionDefLine;
node.columnNumber = functionDefColumn;
node.hitCount = 0;

nodes.append(WTF::move(node));
Expand All @@ -718,8 +840,11 @@ void stopCPUProfiler(JSC::VM& vm, WTF::String* outJSON, WTF::String* outText)

currentParentId = nodeId;

if (i == 0)
if (i == 0) {
nodes[nodeId - 1].hitCount++;
if (sampleLine > 0)
nodes[nodeId - 1].positionTicks.add(sampleLine, 0).iterator->value++;
}
}

samples.append(currentParentId);
Expand Down Expand Up @@ -761,6 +886,26 @@ void stopCPUProfiler(JSC::VM& vm, WTF::String* outJSON, WTF::String* outText)
nodeObj->setValue("children"_s, childrenArray);
}

// Per-line sample counts (Chrome DevTools format). Emit sorted by
// line for deterministic output.
if (!node.positionTicks.isEmpty()) {
WTF::Vector<std::pair<int, int>> sortedTicks;
sortedTicks.reserveInitialCapacity(node.positionTicks.size());
for (auto& entry : node.positionTicks)
sortedTicks.append({ entry.key, entry.value });
std::sort(sortedTicks.begin(), sortedTicks.end(), [](const auto& a, const auto& b) {
return a.first < b.first;
});
auto positionTicksArray = JSON::Array::create();
for (auto& [line, ticks] : sortedTicks) {
auto tickObj = JSON::Object::create();
tickObj->setInteger("line"_s, line);
tickObj->setInteger("ticks"_s, ticks);
positionTicksArray->pushValue(tickObj);
}
nodeObj->setValue("positionTicks"_s, positionTicksArray);
}

nodesArray->pushValue(nodeObj);
}
json->setValue("nodes"_s, nodesArray);
Expand Down
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