Optimized functions discard inlining information when profiling with linux perf (or samply) #63816

Open
Open
Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
Labels
v8 engineIssues and PRs related to the V8 dependency.

Description

@GuillaumeLagrange
GuillaumeLagrange
opened on Jun 9, 2026

Version

v24.15.0

Platform

Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

basic.js

Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.

samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

Yields this profile on my machine that you can load with samply load ./profile.json.gz

profile.json.gz

Image

Notice the lost parent_1->a calls as children of the optimized root_function

How often does it reproduce? Is there a required condition?

100%, at least on x86

What is the expected behavior? Why is that the expected behavior?

Using latest d8 canary

$ ./d8 --version
V8 version 15.0.245.4

Yields this profile

$ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

profile.json.gz

Image

Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
I am using stock node/d8 builds to reduce the number of moving parts

What do you see instead?

We should see the inlined function as we do in the latest d8 build.

Additional information

I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.

I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.

The open question is about backporting

  1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.

Activity

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

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Metadata

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    Labels

    v8 engineIssues and PRs related to the V8 dependency.

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      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions

      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
      Open
      Open
      Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
      Labels
      v8 engineIssues and PRs related to the V8 dependency.
      Description
      @GuillaumeLagrange
      GuillaumeLagrange
      opened on Jun 9, 2026
      Version
      v24.15.0
      Platform
      Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

      Subsystem
      No response
      What steps will reproduce the bug?
      basic.js
      Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
      samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

      Yields this profile on my machine that you can load with samply load ./profile.json.gz
      profile.json.gz
      Image
      Notice the lost parent_1->a calls as children of the optimized root_function
      How often does it reproduce? Is there a required condition?
      100%, at least on x86
      What is the expected behavior? Why is that the expected behavior?
      Using latest d8 canary
      $ ./d8 --version
V8 version 15.0.245.4

      Yields this profile
      $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

      profile.json.gz
      Image
      Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
      
I am using stock node/d8 builds to reduce the number of moving parts
      What do you see instead?
      We should see the inlined function as we do in the latest d8 build.
      Additional information
      I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
      I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
      The open question is about backporting
      1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
      Activity
      Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
      Metadata
      Metadata
      Assignees
      No one assigned
        Labels
        v8 engineIssues and PRs related to the V8 dependency.
        Type
        No type
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
          Open
          Open
          Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
          Labels
          v8 engineIssues and PRs related to the V8 dependency.
          Description
          @GuillaumeLagrange
          GuillaumeLagrange
          opened on Jun 9, 2026
          Version
          v24.15.0
          Platform
          Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

          Subsystem
          No response
          What steps will reproduce the bug?
          basic.js
          Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
          samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

          Yields this profile on my machine that you can load with samply load ./profile.json.gz
          profile.json.gz
          Image
          Notice the lost parent_1->a calls as children of the optimized root_function
          How often does it reproduce? Is there a required condition?
          100%, at least on x86
          What is the expected behavior? Why is that the expected behavior?
          Using latest d8 canary
          $ ./d8 --version
V8 version 15.0.245.4

          Yields this profile
          $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

          profile.json.gz
          Image
          Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
          
I am using stock node/d8 builds to reduce the number of moving parts
          What do you see instead?
          We should see the inlined function as we do in the latest d8 build.
          Additional information
          I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
          I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
          The open question is about backporting
          1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
          Activity
          Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            v8 engineIssues and PRs related to the V8 dependency.
            Type
            No type
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
              Open
              Open
              Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
              Labels
              v8 engineIssues and PRs related to the V8 dependency.
              Description
              @GuillaumeLagrange
              GuillaumeLagrange
              opened on Jun 9, 2026
              Version
              v24.15.0
              Platform
              Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

              Subsystem
              No response
              What steps will reproduce the bug?
              basic.js
              Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
              samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

              Yields this profile on my machine that you can load with samply load ./profile.json.gz
              profile.json.gz
              Image
              Notice the lost parent_1->a calls as children of the optimized root_function
              How often does it reproduce? Is there a required condition?
              100%, at least on x86
              What is the expected behavior? Why is that the expected behavior?
              Using latest d8 canary
              $ ./d8 --version
V8 version 15.0.245.4

              Yields this profile
              $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

              profile.json.gz
              Image
              Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
              
I am using stock node/d8 builds to reduce the number of moving parts
              What do you see instead?
              We should see the inlined function as we do in the latest d8 build.
              Additional information
              I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
              I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
              The open question is about backporting
              1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
              Activity
              Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                v8 engineIssues and PRs related to the V8 dependency.
                Type
                No type
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
                  Open
                  Open
                  Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
                  Labels
                  v8 engineIssues and PRs related to the V8 dependency.
                  Description
                  @GuillaumeLagrange
                  GuillaumeLagrange
                  opened on Jun 9, 2026
                  Version
                  v24.15.0
                  Platform
                  Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

                  Subsystem
                  No response
                  What steps will reproduce the bug?
                  basic.js
                  Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
                  samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                  Yields this profile on my machine that you can load with samply load ./profile.json.gz
                  profile.json.gz
                  Image
                  Notice the lost parent_1->a calls as children of the optimized root_function
                  How often does it reproduce? Is there a required condition?
                  100%, at least on x86
                  What is the expected behavior? Why is that the expected behavior?
                  Using latest d8 canary
                  $ ./d8 --version
V8 version 15.0.245.4

                  Yields this profile
                  $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                  profile.json.gz
                  Image
                  Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
                  
I am using stock node/d8 builds to reduce the number of moving parts
                  What do you see instead?
                  We should see the inlined function as we do in the latest d8 build.
                  Additional information
                  I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
                  I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
                  The open question is about backporting
                  1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
                  Activity
                  Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    v8 engineIssues and PRs related to the V8 dependency.
                    Type
                    No type
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
                      Open
                      Open
                      Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
                      Labels
                      v8 engineIssues and PRs related to the V8 dependency.
                      Description
                      @GuillaumeLagrange
                      GuillaumeLagrange
                      opened on Jun 9, 2026
                      Version
                      v24.15.0
                      Platform
                      Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

                      Subsystem
                      No response
                      What steps will reproduce the bug?
                      basic.js
                      Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
                      samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                      Yields this profile on my machine that you can load with samply load ./profile.json.gz
                      profile.json.gz
                      Image
                      Notice the lost parent_1->a calls as children of the optimized root_function
                      How often does it reproduce? Is there a required condition?
                      100%, at least on x86
                      What is the expected behavior? Why is that the expected behavior?
                      Using latest d8 canary
                      $ ./d8 --version
V8 version 15.0.245.4

                      Yields this profile
                      $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                      profile.json.gz
                      Image
                      Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
                      
I am using stock node/d8 builds to reduce the number of moving parts
                      What do you see instead?
                      We should see the inlined function as we do in the latest d8 build.
                      Additional information
                      I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
                      I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
                      The open question is about backporting
                      1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
                      Activity
                      Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        v8 engineIssues and PRs related to the V8 dependency.
                        Type
                        No type
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
                          Open
                          Open
                          Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
                          Labels
                          v8 engineIssues and PRs related to the V8 dependency.
                          Description
                          @GuillaumeLagrange
                          GuillaumeLagrange
                          opened on Jun 9, 2026
                          Version
                          v24.15.0
                          Platform
                          Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

                          Subsystem
                          No response
                          What steps will reproduce the bug?
                          basic.js
                          Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
                          samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                          Yields this profile on my machine that you can load with samply load ./profile.json.gz
                          profile.json.gz
                          Image
                          Notice the lost parent_1->a calls as children of the optimized root_function
                          How often does it reproduce? Is there a required condition?
                          100%, at least on x86
                          What is the expected behavior? Why is that the expected behavior?
                          Using latest d8 canary
                          $ ./d8 --version
V8 version 15.0.245.4

                          Yields this profile
                          $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                          profile.json.gz
                          Image
                          Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
                          
I am using stock node/d8 builds to reduce the number of moving parts
                          What do you see instead?
                          We should see the inlined function as we do in the latest d8 build.
                          Additional information
                          I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
                          I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
                          The open question is about backporting
                          1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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                              Optimized functions discard inlining information when profiling with linux perf (or samply) #63816
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                              Open
                              Optimized functions discard inlining information when profiling with linux perf (or samply)#63816
                              Labels
                              v8 engineIssues and PRs related to the V8 dependency.
                              Description
                              @GuillaumeLagrange
                              GuillaumeLagrange
                              opened on Jun 9, 2026
                              Version
                              v24.15.0
                              Platform
                              Linux badlands 6.12.91 #1-NixOS SMP PREEMPT_DYNAMIC Sat May 23 11:05:02 UTC 2026 x86_64 GNU/Linux

                              Subsystem
                              No response
                              What steps will reproduce the bug?
                              basic.js
                              Using samply for profiling for simplicity, but the result is the same using perf record, then perf inject then the folding flamegraph scripts.
                              samply record -- node --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                              Yields this profile on my machine that you can load with samply load ./profile.json.gz
                              profile.json.gz
                              Image
                              Notice the lost parent_1->a calls as children of the optimized root_function
                              How often does it reproduce? Is there a required condition?
                              100%, at least on x86
                              What is the expected behavior? Why is that the expected behavior?
                              Using latest d8 canary
                              $ ./d8 --version
V8 version 15.0.245.4

                              Yields this profile
                              $ samply record -- ./d8 --perf-prof --interpreted-frames-native-stack --expose-gc --allow-natives-syntax basic.js

                              profile.json.gz
                              Image
                              Note: the root function is transformed into a Builtin::EntryTrampoline because of this bug: https://issues.chromium.org/issues/520898842
                              
I am using stock node/d8 builds to reduce the number of moving parts
                              What do you see instead?
                              We should see the inlined function as we do in the latest d8 build.
                              Additional information
                              I was not able to test with a stock node 26 build because it seems that it output corrupted jit dumps on my machine for an unrelated issue.
                              I have a patch that backported some of the v8 changes into the node24 branch and seemed to fix the issue, which I would be interested to submit.
                              The open question is about backporting
                              1. Is the team willing to backport this? Since node 24 will not be deprecated until 2027, this would help improve linux perf profiling.
                              Activity
                              Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
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