From 76c62e509b31fa31a537da94966cbd2971dfa79b Mon Sep 17 00:00:00 2001
From: Brandon Black <bblack@wikimedia.org>
Date: Tue, 2 Sep 2025 12:20:11 -0500
Subject: [PATCH] Fix cmsghdr struct for the *nixes

Previously we had a single definition of std.c.cmsghdr for all
libc-linking platforms which aliased from the Solaris definition,
a superfluous matching one in std.os.dragonfly, and no others.

The existing definition from std.c didn't actually work for Linux,
as Linux's "len" field is usize in the kernel's definition.

Emscripten follows the Linux model of course (but uses the
binary-compatible musl definition, which has an endian-sensitive
padding scheme to make the len type "socklen_t" even though the
kernel uses a usize, which is fair).

This unifies and documents all the known *nix-ish cases (I'm not
sure if wasi or windows really has cmsghdr support? Could be added
later, void for now), such that c.cmsghdr and posix.system.cmsghdr
should work correctly for all the known cases here, libc or
otherwise.
---
 lib/std/c.zig           | 34 +++++++++++++++++++++++++++++++++-
 lib/std/c/dragonfly.zig |  6 ------
 lib/std/c/solaris.zig   |  6 ------
 lib/std/os/linux.zig    |  7 +++++++
 4 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/lib/std/c.zig b/lib/std/c.zig
index 380aad88f5..4b869bf2e4 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -4171,6 +4171,39 @@ pub const msghdr_const = switch (native_os) {
     },
     else => void,
 };
+pub const cmsghdr = switch (native_os) {
+    // https://github.com/emscripten-core/emscripten/blob/96371ed7888fc78c040179f4d4faa82a6a07a116/system/lib/libc/musl/include/sys/socket.h#L44
+    .linux, .emscripten => linux.cmsghdr,
+    // https://github.com/freebsd/freebsd-src/blob/b197d2abcb6895d78bc9df8404e374397aa44748/sys/sys/socket.h#L492
+    .freebsd,
+    // https://github.com/DragonFlyBSD/DragonFlyBSD/blob/107c0518337ba90e7fa49e74845d8d44320c9a6d/sys/sys/socket.h#L452
+    .dragonfly,
+    // https://github.com/NetBSD/src/blob/ba8e1774fd9c0c26ecca461c07bc95d9ebb69579/sys/sys/socket.h#L528
+    .netbsd,
+    // https://github.com/openbsd/src/blob/master/sys/sys/socket.h#L527
+    .openbsd,
+    // https://github.com/kofemann/opensolaris/blob/80192cd83bf665e708269dae856f9145f7190f74/usr/src/uts/common/sys/socket.h#L416
+    .solaris,
+    // https://github.com/illumos/illumos-gate/blob/afdf2e523873cb523df379676067bf9785a0f456/usr/src/uts/common/sys/socket.h#L460
+    .illumos,
+    // https://github.com/SerenityOS/serenity/blob/4ee360a348a5e2490eeaeeabb3eb19e70dd450eb/Kernel/API/POSIX/sys/socket.h#L68
+    .serenity,
+    // https://github.com/haiku/haiku/blob/b54f586058fd6623645512e4631468cede9933b9/headers/posix/sys/socket.h#L132
+    .haiku,
+    // https://github.com/apple/darwin-xnu/blob/2ff845c2e033bd0ff64b5b6aa6063a1f8f65aa32/bsd/sys/socket.h#L1041
+    .macos,
+    .driverkit,
+    .ios,
+    .tvos,
+    .visionos,
+    .watchos,
+    => extern struct {
+        len: socklen_t,
+        level: c_int,
+        type: c_int,
+    },
+    else => void,
+};
 pub const nfds_t = switch (native_os) {
     .linux => linux.nfds_t,
     .emscripten => emscripten.nfds_t,
@@ -11010,7 +11043,6 @@ pub const SCM = solaris.SCM;
 pub const SETCONTEXT = solaris.SETCONTEXT;
 pub const SETUSTACK = solaris.GETUSTACK;
 pub const SFD = solaris.SFD;
-pub const cmsghdr = solaris.cmsghdr;
 pub const ctid_t = solaris.ctid_t;
 pub const file_obj = solaris.file_obj;
 pub const fpregset_t = solaris.fpregset_t;
diff --git a/lib/std/c/dragonfly.zig b/lib/std/c/dragonfly.zig
index cb33fc1e56..c06d7ab8f5 100644
--- a/lib/std/c/dragonfly.zig
+++ b/lib/std/c/dragonfly.zig
@@ -158,12 +158,6 @@ pub const BADSIG = SIG.ERR;
 
 pub const sig_t = *const fn (i32) callconv(.c) void;
 
-pub const cmsghdr = extern struct {
-    len: socklen_t,
-    level: c_int,
-    type: c_int,
-};
-
 pub const cmsgcred = extern struct {
     pid: pid_t,
     uid: uid_t,
diff --git a/lib/std/c/solaris.zig b/lib/std/c/solaris.zig
index df7dbca16a..91d96527d9 100644
--- a/lib/std/c/solaris.zig
+++ b/lib/std/c/solaris.zig
@@ -31,12 +31,6 @@ pub const poolid_t = id_t;
 pub const zoneid_t = id_t;
 pub const ctid_t = id_t;
 
-pub const cmsghdr = extern struct {
-    len: socklen_t,
-    level: i32,
-    type: i32,
-};
-
 pub const SCM = struct {
     pub const UCRED = 0x1012;
     pub const RIGHTS = 0x1010;
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index 7db0634271..f5ff7767a8 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -9709,6 +9709,13 @@ pub const msghdr_const = extern struct {
     flags: u32,
 };
 
+// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/socket.h?id=b320789d6883cc00ac78ce83bccbfe7ed58afcf0#n105
+pub const cmsghdr = extern struct {
+    len: usize,
+    level: i32,
+    type: i32,
+};
+
 /// The syscalls, but with Zig error sets, going through libc if linking libc,
 /// and with some footguns eliminated.
 pub const wrapped = struct {