doc: document per-architecture fast FFI argument limits#65207

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27 changes: 20 additions & 7 deletions doc/api/ffi.md
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading
, '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" + '

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doc: document per-architecture fast FFI argument limits#65207

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doc: document per-architecture fast FFI argument limits
#65207
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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading

, '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('^' + ".*" + '

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doc: document per-architecture fast FFI argument limits#65207

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 Merged

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merged 1 commit into

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doc: document per-architecture fast FFI argument limits
#65207
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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading

, '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
doc: document per-architecture fast FFI argument limits#65207

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 Merged

nodejs-github-bot
merged 1 commit into

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Aug 18, 2026

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−7

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doc: document per-architecture fast FFI argument limits
#65207
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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading

, '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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doc: document per-architecture fast FFI argument limits
#65207
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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading

, '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
doc: document per-architecture fast FFI argument limits#65207

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 Merged

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merged 1 commit into

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Aug 18, 2026

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−7

 Merged


doc: document per-architecture fast FFI argument limits
#65207
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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading

, '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
doc: document per-architecture fast FFI argument limits#65207

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doc: document per-architecture fast FFI argument limits
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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
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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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 Merged

nodejs-github-bot
merged 1 commit into

from

Aug 18, 2026

+20

−7

 Merged


doc: document per-architecture fast FFI argument limits
#65207
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Commits

Show all changes


1 commit


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27 changes: 20 additions & 7 deletions
doc/api/ffi.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -126,13 +126,26 @@ raw pointer `bigint` values. For pointer-like parameters, `null`, `undefined`,
strings, `Buffer`, typed array, `DataView`, and `ArrayBuffer` values are
converted on the JavaScript side before calling the optimized native wrapper.

Optimized Fast FFI calls support at most 8 function arguments, but the exact
limit depends on the architecture and on the argument types, because each
argument must fit in the registers used by the platform trampoline. Integer
and pointer arguments are limited to 7 on AArch64 and to 6 on x86-64, while
floating-point arguments can use up to 8 on both. Functions that exceed these
limits, including any function with more than 8 arguments, use the generic FFI
call path instead.
Optimized Fast FFI calls fall back to the generic FFI call path when a
function's arguments or return type do not fit the platform-specific fast
trampoline. Fast FFI calls support at most 8 total arguments, and the
register and argument limits differ per architecture:

| Architecture | Max integer/pointer args | Max floating-point args | Buffer-shaped args | Buffer-shaped + FP together | Narrow (8/16-bit) return |
| -------------------------- | ----------------------------------------- | ----------------------- | ------------------ | --------------------------- | ------------------------ |
| AArch64 | 7 (6 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Linux/macOS (SysV) | 6 (4 when a buffer-shaped arg is present) | 8 | Supported | Not supported | Supported |
| x86-64, Windows (Win64) | 3 (total arguments also capped at 3) | 3 | Not supported | N/A | Supported |
| s390x | 4 | 4 | Not supported | N/A | Not supported |
| PPC64LE | 7 | 8 | Not supported | N/A | Not supported |
| LoongArch64 | 7 | 8 | Not supported | N/A | Not supported |
| RISC-V (64-bit) | 7 | 8 | Not supported | N/A | Not supported |

PPC64BE has no fast-call trampoline and always uses the generic call path.
"Buffer-shaped args" means `Buffer`, typed array, `DataView`, or `ArrayBuffer`
values passed as pointer-like arguments. Functions whose argument or return
types exceed the limits for the current platform use the generic FFI call
path instead.

## Signature objects

Expand Down
Loading