From 8372b50a6faa2883a6bd15fde121fcb47e6d43e9 Mon Sep 17 00:00:00 2001
From: dybucc <149513579+dybucc@users.noreply.github.com>
Date: Thu, 18 Jun 2026 15:53:52 +0200
Subject: [PATCH 1/2] feat: add macro to declare unstable constants

This patch adds a new macro that can be used for declaring constants
when these are known to possibly change upstream across target OS/ABI
versions.
---
 src/macros.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/macros.rs b/src/macros.rs
index 0149b1fd18466..5c5b8c2deac79 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -402,6 +402,21 @@ macro_rules! offset_of {
     }};
 }
 
+/// Defines constants with an accompanying doc comment pointing out their
+/// instability, and links to the crate documentation for usage guidelines.
+macro_rules! ct {
+    ($($it:item)+) => {
+$(
+/// This constant, among others often used in C for the purposes of denoting the
+/// latest value or limit in a set of constants, is likely to change upstream.
+/// For correct usage, see the [crate-level documentation][docs].
+///
+/// [docs]: index.html#usage-recommendations
+$it
+)+
+    };
+}
+
 #[cfg(test)]
 mod tests {
     use core::any::TypeId;

From d6d6fcdf33cfa4b64a1cea178227a9be5feba4af Mon Sep 17 00:00:00 2001
From: dybucc <149513579+dybucc@users.noreply.github.com>
Date: Thu, 28 May 2026 11:59:50 +0200
Subject: [PATCH 2/2] refactor: annotate *LAST constants as unstable

Constants matching the *LAST naming scheme, and whose purpose fits that
of a "delimitter" value have been annotated with a documentation comment
pointing to updated usage guidelines for the libc crate.
---
 src/solid/mod.rs                       |  5 ++++-
 src/unix/bsd/netbsdlike/openbsd/mod.rs |  5 ++++-
 src/unix/linux_like/android/mod.rs     | 15 ++++++++++++---
 src/unix/linux_like/linux/mod.rs       | 22 +++++++++++++++++-----
 src/unix/solarish/illumos.rs           |  4 +++-
 src/unix/solarish/solaris.rs           |  4 +++-
 6 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/src/solid/mod.rs b/src/solid/mod.rs
index 0182f8150df67..a4d653bca70d1 100644
--- a/src/solid/mod.rs
+++ b/src/solid/mod.rs
@@ -219,7 +219,10 @@ pub const LC_MONETARY: c_int = 3;
 pub const LC_NUMERIC: c_int = 4;
 pub const LC_TIME: c_int = 5;
 pub const LC_MESSAGES: c_int = 6;
-pub const _LC_LAST: c_int = 7;
+
+ct! {
+    pub const _LC_LAST: c_int = 7;
+}
 
 pub const EPERM: c_int = 1;
 pub const ENOENT: c_int = 2;
diff --git a/src/unix/bsd/netbsdlike/openbsd/mod.rs b/src/unix/bsd/netbsdlike/openbsd/mod.rs
index 6242505420559..96c0aca7204c2 100644
--- a/src/unix/bsd/netbsdlike/openbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/openbsd/mod.rs
@@ -1736,7 +1736,10 @@ pub const LC_NUMERIC_MASK: c_int = 1 << crate::LC_NUMERIC;
 pub const LC_TIME_MASK: c_int = 1 << crate::LC_TIME;
 pub const LC_MESSAGES_MASK: c_int = 1 << crate::LC_MESSAGES;
 
-const _LC_LAST: c_int = 7;
+ct! {
+    const _LC_LAST: c_int = 7;
+}
+
 pub const LC_ALL_MASK: c_int = (1 << _LC_LAST) - 2;
 
 pub const LC_GLOBAL_LOCALE: crate::locale_t = -1isize as crate::locale_t;
diff --git a/src/unix/linux_like/android/mod.rs b/src/unix/linux_like/android/mod.rs
index b262ff8a142c7..ee9a80ceb60e4 100644
--- a/src/unix/linux_like/android/mod.rs
+++ b/src/unix/linux_like/android/mod.rs
@@ -1937,7 +1937,10 @@ pub const NF_BR_PRI_BRNF: c_int = 0;
 pub const NF_BR_PRI_NAT_DST_OTHER: c_int = 100;
 pub const NF_BR_PRI_FILTER_OTHER: c_int = 200;
 pub const NF_BR_PRI_NAT_SRC: c_int = 300;
-pub const NF_BR_PRI_LAST: c_int = crate::INT_MAX;
+
+ct! {
+    pub const NF_BR_PRI_LAST: c_int = crate::INT_MAX;
+}
 
 // linux/netfilter_ipv4.h
 pub const NF_IP_PRE_ROUTING: c_int = 0;
@@ -1961,7 +1964,10 @@ pub const NF_IP_PRI_NAT_SRC: c_int = 100;
 pub const NF_IP_PRI_SELINUX_LAST: c_int = 225;
 pub const NF_IP_PRI_CONNTRACK_HELPER: c_int = 300;
 pub const NF_IP_PRI_CONNTRACK_CONFIRM: c_int = crate::INT_MAX;
-pub const NF_IP_PRI_LAST: c_int = crate::INT_MAX;
+
+ct! {
+    pub const NF_IP_PRI_LAST: c_int = crate::INT_MAX;
+}
 
 // linux/netfilter_ipv6.h
 pub const NF_IP6_PRE_ROUTING: c_int = 0;
@@ -1984,7 +1990,10 @@ pub const NF_IP6_PRI_SECURITY: c_int = 50;
 pub const NF_IP6_PRI_NAT_SRC: c_int = 100;
 pub const NF_IP6_PRI_SELINUX_LAST: c_int = 225;
 pub const NF_IP6_PRI_CONNTRACK_HELPER: c_int = 300;
-pub const NF_IP6_PRI_LAST: c_int = crate::INT_MAX;
+
+ct! {
+    pub const NF_IP6_PRI_LAST: c_int = crate::INT_MAX;
+}
 
 // linux/netfilter_ipv6/ip6_tables.h
 pub const IP6T_SO_ORIGINAL_DST: c_int = 80;
diff --git a/src/unix/linux_like/linux/mod.rs b/src/unix/linux_like/linux/mod.rs
index 081b16d78ce39..b50b9e174b852 100644
--- a/src/unix/linux_like/linux/mod.rs
+++ b/src/unix/linux_like/linux/mod.rs
@@ -2180,7 +2180,10 @@ pub const NF_BR_PRI_BRNF: c_int = 0;
 pub const NF_BR_PRI_NAT_DST_OTHER: c_int = 100;
 pub const NF_BR_PRI_FILTER_OTHER: c_int = 200;
 pub const NF_BR_PRI_NAT_SRC: c_int = 300;
-pub const NF_BR_PRI_LAST: c_int = crate::INT_MAX;
+
+ct! {
+    pub const NF_BR_PRI_LAST: c_int = crate::INT_MAX;
+}
 
 // linux/netfilter_ipv4.h
 pub const NF_IP_PRE_ROUTING: c_int = 0;
@@ -2204,7 +2207,10 @@ pub const NF_IP_PRI_NAT_SRC: c_int = 100;
 pub const NF_IP_PRI_SELINUX_LAST: c_int = 225;
 pub const NF_IP_PRI_CONNTRACK_HELPER: c_int = 300;
 pub const NF_IP_PRI_CONNTRACK_CONFIRM: c_int = crate::INT_MAX;
-pub const NF_IP_PRI_LAST: c_int = crate::INT_MAX;
+
+ct! {
+    pub const NF_IP_PRI_LAST: c_int = crate::INT_MAX;
+}
 
 // linux/netfilter_ipv6.h
 pub const NF_IP6_PRE_ROUTING: c_int = 0;
@@ -2227,7 +2233,10 @@ pub const NF_IP6_PRI_SECURITY: c_int = 50;
 pub const NF_IP6_PRI_NAT_SRC: c_int = 100;
 pub const NF_IP6_PRI_SELINUX_LAST: c_int = 225;
 pub const NF_IP6_PRI_CONNTRACK_HELPER: c_int = 300;
-pub const NF_IP6_PRI_LAST: c_int = crate::INT_MAX;
+
+ct! {
+    pub const NF_IP6_PRI_LAST: c_int = crate::INT_MAX;
+}
 
 // linux/netfilter_ipv6/ip6_tables.h
 pub const IP6T_SO_ORIGINAL_DST: c_int = 80;
@@ -2304,10 +2313,13 @@ pub const SIOCGIWENCODEEXT: c_ulong = 0x8B35;
 pub const SIOCSIWPMKSA: c_ulong = 0x8B36;
 
 pub const SIOCIWFIRSTPRIV: c_ulong = 0x8BE0;
-pub const SIOCIWLASTPRIV: c_ulong = 0x8BFF;
+
+ct! {
+    pub const SIOCIWLASTPRIV: c_ulong = 0x8BFF;
+    pub const SIOCIWLAST: c_ulong = SIOCIWLASTPRIV;
+}
 
 pub const SIOCIWFIRST: c_ulong = 0x8B00;
-pub const SIOCIWLAST: c_ulong = SIOCIWLASTPRIV;
 
 pub const IWEVTXDROP: c_ulong = 0x8C00;
 pub const IWEVQUAL: c_ulong = 0x8C01;
diff --git a/src/unix/solarish/illumos.rs b/src/unix/solarish/illumos.rs
index b31c31bd1f6c8..8112f05aab0be 100644
--- a/src/unix/solarish/illumos.rs
+++ b/src/unix/solarish/illumos.rs
@@ -152,7 +152,9 @@ pub const LOCK_EX: c_int = 2;
 pub const LOCK_NB: c_int = 4;
 pub const LOCK_UN: c_int = 8;
 
-pub const _PC_LAST: c_int = 101;
+ct! {
+    pub const _PC_LAST: c_int = 101;
+}
 
 pub const _CS_PATH: c_int = 65;
 
diff --git a/src/unix/solarish/solaris.rs b/src/unix/solarish/solaris.rs
index 992df9ddc0ad9..bf331b28456a9 100644
--- a/src/unix/solarish/solaris.rs
+++ b/src/unix/solarish/solaris.rs
@@ -132,7 +132,9 @@ pub const F_DUPFD_CLOFORK: c_int = 49;
 pub const F_DUP2FD_CLOEXEC: c_int = 48;
 pub const F_DUP2FD_CLOFORK: c_int = 50;
 
-pub const _PC_LAST: c_int = 102;
+ct! {
+    pub const _PC_LAST: c_int = 102;
+}
 
 pub const PRIV_PROC_SENSITIVE: c_uint = 0x0008;
 pub const PRIV_PFEXEC_AUTH: c_uint = 0x0200;