[Wasm] Write barriers - #128225

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kg:wasm-writebarriers-callconv
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[Wasm] Write barriers#128225
kg merged 12 commits into
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kg:wasm-writebarriers-callconv

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Sufficient for the R2R'd version of this to run without crashing:

staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}

Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.

This PR:

  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files

CopilotAI review requested due to automatic review settings May 14, 2026 20:11
@kgkg added the arch-wasm WebAssembly architecture label May 14, 2026
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Pull request overview

Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.

Changes:

  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.

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Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

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Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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var __m = "github.com";
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[Wasm] Write barriers - #128225
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kg:wasm-writebarriers-callconv
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[Wasm] Write barriers#128225
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.
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, '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");
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})();
(function(){
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var __re = new RegExp('^' + ".*" + '

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[Wasm] Write barriers - #128225
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kg merged 12 commits into
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kg:wasm-writebarriers-callconv
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[Wasm] Write barriers#128225
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
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, '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('^' + ".*" + '

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[Wasm] Write barriers - #128225
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kg:wasm-writebarriers-callconv
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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, '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" + '

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[Wasm] Write barriers - #128225
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kg:wasm-writebarriers-callconv
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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, '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");
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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[Wasm] Write barriers - #128225
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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Comment threadsrc/coreclr/jit/codegenwasm.cpp
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, '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('^' + ".*" + '

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[Wasm] Write barriers - #128225
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kg:wasm-writebarriers-callconv
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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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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[Wasm] Write barriers - #128225
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kg:wasm-writebarriers-callconv
May 22, 2026
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[Wasm] Write barriers#128225
kg merged 12 commits into
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kg:wasm-writebarriers-callconv
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Sufficient for the R2R'd version of this to run without crashing:
staticstring?TestField;[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticvoidConcatTwoStrings(stringa,stringb){TestField=a+b;}[MethodImpl(MethodImplOptions.NoOptimization|MethodImplOptions.NoInlining)]publicstaticintMain(){Console.WriteLine("Hello world!");ConcatTwoStrings("A","B");Console.WriteLine(TestField);return42;}
Currently the write barrier in ConcatTwoStrings fails due to the calling convention being wrong and then once the calling convention is fixed, it fails because we didn't implement the write barriers yet.
This PR:
  • Updates the calling convention of the write barriers to match that expected by the JIT (bare calling convention without sp/pep args) by adding new FCDECL2_RAW / FCIMPL2_RAW macros
  • Fixes RhpByRefAssignRef's signature being incorrect (missing *)
  • Disables RhpByRefAssignRef on Wasm
  • Updates genCodeForStoreBlk to not use RhpByRefAssignRef anymore
  • Implements the checked and unchecked write barriers in inline wasm assembly in the new wasm/writebarriers.cpp file
  • Cleans up various misleading comments in our inline assembly files
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Pull request overview
Initial scaffolding to make the WASM portable write barriers (RhpAssignRef, RhpCheckedAssignRef, RhpByRefAssignRef) use a "raw" calling convention that matches what RyuJIT expects for write barriers, rather than the trampolined WASM FCALL convention that threads callersStackPointer / portableEntryPointContext through. The actual barrier implementations still assert and will be filled in later.
Changes:
  • Add new FCDECL2_RAW / FCIMPL2_RAW macros that bypass the WASM stack-pointer/entrypoint-context plumbing and define the function with the plain (a1, a2) signature; provide non-WASM fallbacks that alias to FCDECL2 / FCIMPL2.
  • Switch the three Rhp*AssignRef declarations in jitinterface.h and definitions in WriteBarriers.cpp to the new _RAW variants.
  • Trivial whitespace cleanup in jitinterface.h.
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FileDescription
src/coreclr/vm/fcall.hAdds WASM-specific FCDECL2_RAW / FCIMPL2_RAW macros and non-WASM fallbacks aliasing to the standard FCDECL2 / FCIMPL2.
src/coreclr/vm/jitinterface.hSwitches Rhp{Checked,ByRef,}AssignRef declarations to FCDECL2_RAW; trims trailing whitespace.
src/coreclr/runtime/portable/WriteBarriers.cppUpdates the three portable write-barrier stubs to use FCDECL2_RAW / FCIMPL2_RAW.
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Pull request overview
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Pull request overview
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