diff --git a/src/fuchsia/mod.rs b/src/fuchsia/mod.rs
index 834d4e9fac2b7..69fbdd9696ff2 100644
--- a/src/fuchsia/mod.rs
+++ b/src/fuchsia/mod.rs
@@ -1592,6 +1592,8 @@ pub const LOCK_UN: c_int = 8;
 pub const SS_ONSTACK: c_int = 1;
 pub const SS_DISABLE: c_int = 2;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 4096;
 
 pub const FD_SETSIZE: c_int = 1024;
diff --git a/src/new/linux_uapi/linux/can/j1939.rs b/src/new/linux_uapi/linux/can/j1939.rs
index fdf425ce6c0c1..f3e04eee407f5 100644
--- a/src/new/linux_uapi/linux/can/j1939.rs
+++ b/src/new/linux_uapi/linux/can/j1939.rs
@@ -57,4 +57,6 @@ s! {
     }
 }
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const J1939_FILTER_MAX: c_int = 512;
diff --git a/src/new/linux_uapi/linux/can/raw.rs b/src/new/linux_uapi/linux/can/raw.rs
index 470334bd5d147..6e07cd8eb6a14 100644
--- a/src/new/linux_uapi/linux/can/raw.rs
+++ b/src/new/linux_uapi/linux/can/raw.rs
@@ -3,6 +3,9 @@
 pub use crate::linux::can::*;
 
 pub const SOL_CAN_RAW: c_int = SOL_CAN_BASE + CAN_RAW;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const CAN_RAW_FILTER_MAX: c_int = 512;
 
 // FIXME(cleanup): use `c_enum!`, which needs to be adapted to allow omitting a type.
diff --git a/src/new/qurt/limits.rs b/src/new/qurt/limits.rs
index fefe069c1c19f..18f2151d4d4d4 100644
--- a/src/new/qurt/limits.rs
+++ b/src/new/qurt/limits.rs
@@ -27,12 +27,24 @@ pub const USHRT_MAX: c_ushort = 65535;
 // POSIX Limits
 pub const ARG_MAX: c_int = 4096;
 pub const CHILD_MAX: c_int = 25;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const LINK_MAX: c_int = 8;
+
 pub const MAX_CANON: c_int = 255;
 pub const MAX_INPUT: c_int = 255;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NAME_MAX: c_int = 255;
+
 pub const OPEN_MAX: c_int = 20;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 260;
+
 pub const PIPE_BUF: c_int = 512;
 pub const STREAM_MAX: c_int = 20;
 pub const TZNAME_MAX: c_int = 50;
diff --git a/src/new/qurt/signal.rs b/src/new/qurt/signal.rs
index e5a219af5881b..bd14a8423244f 100644
--- a/src/new/qurt/signal.rs
+++ b/src/new/qurt/signal.rs
@@ -51,6 +51,9 @@ pub const SIG_SETMASK: c_int = 3;
 pub const POSIX_MSG: c_int = 7;
 pub const POSIX_NOTIF: c_int = 8;
 pub const SIGRTMIN: c_int = 10;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SIGRTMAX: c_int = 32;
 
 // Notification types (from QuRT signal.h)
diff --git a/src/unix/aix/mod.rs b/src/unix/aix/mod.rs
index 04df0b6ba336d..d5da6372e2369 100644
--- a/src/unix/aix/mod.rs
+++ b/src/unix/aix/mod.rs
@@ -932,7 +932,11 @@ pub const RTAX_IFP: c_int = 4;
 pub const RTAX_IFA: c_int = 5;
 pub const RTAX_AUTHOR: c_int = 6;
 pub const RTAX_BRD: c_int = 7;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTAX_MAX: c_int = 8;
+
 pub const RTF_UP: c_int = 0x1;
 pub const RTF_GATEWAY: c_int = 0x2;
 pub const RTF_HOST: c_int = 0x4;
@@ -1445,7 +1449,11 @@ pub const L_GETPROCINFO: c_int = 7;
 pub const L_GETXINFO: c_int = 8;
 
 // sys/limits.h
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 1023;
+
 pub const PAGESIZE: c_int = 4096;
 pub const IOV_MAX: c_int = 16;
 pub const AIO_LISTIO_MAX: c_int = 4096;
@@ -1454,14 +1462,37 @@ pub const OPEN_MAX: c_int = 65534;
 pub const MAX_INPUT: c_int = 512;
 pub const MAX_CANON: c_int = 256;
 pub const ARG_MAX: c_int = 1048576;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_BASE_MAX: c_int = 99;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_DIM_MAX: c_int = 0x800;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_SCALE_MAX: c_int = 99;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_STRING_MAX: c_int = 0x800;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const CHARCLASS_NAME_MAX: c_int = 14;
+
 pub const CHILD_MAX: c_int = 128;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const COLL_WEIGHTS_MAX: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const EXPR_NEST_MAX: c_int = 32;
+
 pub const NZERO: c_int = 20;
 
 // sys/lockf.h
@@ -1541,7 +1572,11 @@ pub const MAXPATHLEN: c_int = PATH_MAX + 1;
 pub const MAXSYMLINKS: c_int = 20;
 pub const MAXHOSTNAMELEN: c_int = 256;
 pub const MAXUPRC: c_int = 128;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NGROUPS_MAX: c_ulong = 2048;
+
 pub const NGROUPS: c_ulong = NGROUPS_MAX;
 pub const NOFILE: c_int = OPEN_MAX;
 
@@ -1739,7 +1774,11 @@ pub const SIGXCPU: c_int = 24;
 pub const SIGXFSZ: c_int = 25;
 pub const SIGTRAP: c_int = 5;
 pub const SIGCLD: c_int = 20;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SIGRTMAX: c_int = 57;
+
 pub const SIGRTMIN: c_int = 50;
 pub const SI_USER: c_int = 0;
 pub const SI_UNDEFINED: c_int = 8;
@@ -1817,7 +1856,11 @@ pub const AF_INET6: c_int = 24;
 pub const AF_INTF: c_int = 20;
 pub const AF_RIF: c_int = 21;
 pub const AF_NDD: c_int = 23;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const AF_MAX: c_int = 30;
+
 pub const PF_UNSPEC: c_int = AF_UNSPEC;
 pub const PF_UNIX: c_int = AF_UNIX;
 pub const PF_INET: c_int = AF_INET;
@@ -1843,7 +1886,11 @@ pub const PF_RIF: c_int = AF_RIF;
 pub const PF_INTF: c_int = AF_INTF;
 pub const PF_NDD: c_int = AF_NDD;
 pub const PF_INET6: c_int = AF_INET6;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PF_MAX: c_int = AF_MAX;
+
 pub const SF_CLOSE: c_int = 1;
 pub const SF_REUSE: c_int = 2;
 pub const SF_DONT_CACHE: c_int = 4;
diff --git a/src/unix/bsd/apple/mod.rs b/src/unix/bsd/apple/mod.rs
index 63e1b51546b1f..60fc88006c22a 100644
--- a/src/unix/bsd/apple/mod.rs
+++ b/src/unix/bsd/apple/mod.rs
@@ -2014,6 +2014,9 @@ pub const CPU_STATE_USER: c_int = 0;
 pub const CPU_STATE_SYSTEM: c_int = 1;
 pub const CPU_STATE_IDLE: c_int = 2;
 pub const CPU_STATE_NICE: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const CPU_STATE_MAX: c_int = 4;
 
 pub const PROCESSOR_BASIC_INFO: c_int = 1;
@@ -3399,14 +3402,39 @@ pub const HW_TARGET: c_int = 26;
 pub const HW_PRODUCT: c_int = 27;
 pub const HW_MAXID: c_int = 28;
 pub const USER_CS_PATH: c_int = 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_BASE_MAX: c_int = 2;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_DIM_MAX: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_SCALE_MAX: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_STRING_MAX: c_int = 5;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_EXPR_NEST_MAX: c_int = 7;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_LINE_MAX: c_int = 8;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_RE_DUP_MAX: c_int = 9;
+
 pub const USER_POSIX2_VERSION: c_int = 10;
 pub const USER_POSIX2_C_BIND: c_int = 11;
 pub const USER_POSIX2_C_DEV: c_int = 12;
@@ -3450,10 +3478,6 @@ pub const SIGEV_THREAD: c_int = 3;
 pub const AIO_CANCELED: c_int = 2;
 pub const AIO_NOTCANCELED: c_int = 4;
 pub const AIO_ALLDONE: c_int = 1;
-#[deprecated(
-    since = "0.2.64",
-    note = "Can vary at runtime.  Use sysconf(3) instead"
-)]
 pub const AIO_LISTIO_MAX: c_int = 16;
 pub const LIO_NOP: c_int = 0;
 pub const LIO_WRITE: c_int = 2;
@@ -3529,6 +3553,8 @@ pub const RTV_SSTHRESH: c_int = 0x20;
 pub const RTV_RTT: c_int = 0x40;
 pub const RTV_RTTVAR: c_int = 0x80;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTAX_MAX: c_int = 8;
 
 pub const KERN_PROCARGS2: c_int = 49;
diff --git a/src/unix/bsd/freebsdlike/dragonfly/mod.rs b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
index 6c630c197f377..23af9aeacd2b5 100644
--- a/src/unix/bsd/freebsdlike/dragonfly/mod.rs
+++ b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
@@ -645,14 +645,39 @@ pub const HW_MACHINE_PLATFORM: c_int = 12;
 pub const HW_SENSORS: c_int = 13;
 pub const HW_MAXID: c_int = 14;
 pub const USER_CS_PATH: c_int = 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_BASE_MAX: c_int = 2;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_DIM_MAX: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_SCALE_MAX: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_STRING_MAX: c_int = 5;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_EXPR_NEST_MAX: c_int = 7;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_LINE_MAX: c_int = 8;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_RE_DUP_MAX: c_int = 9;
+
 pub const USER_POSIX2_VERSION: c_int = 10;
 pub const USER_POSIX2_C_BIND: c_int = 11;
 pub const USER_POSIX2_C_DEV: c_int = 12;
@@ -1172,6 +1197,9 @@ pub const RTM_VERSION: c_int = 7;
 pub const RTAX_MPLS1: c_int = 8;
 pub const RTAX_MPLS2: c_int = 9;
 pub const RTAX_MPLS3: c_int = 10;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTAX_MAX: c_int = 11;
 
 const fn _CMSG_ALIGN(n: usize) -> usize {
diff --git a/src/unix/bsd/freebsdlike/freebsd/mod.rs b/src/unix/bsd/freebsdlike/freebsd/mod.rs
index 453f4dcfbda23..ddfb516d7dfdf 100644
--- a/src/unix/bsd/freebsdlike/freebsd/mod.rs
+++ b/src/unix/bsd/freebsdlike/freebsd/mod.rs
@@ -2320,14 +2320,39 @@ pub const HW_MACHINE_ARCH: c_int = 11;
 pub const HW_REALMEM: c_int = 12;
 
 pub const USER_CS_PATH: c_int = 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_BASE_MAX: c_int = 2;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_DIM_MAX: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_SCALE_MAX: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_STRING_MAX: c_int = 5;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_EXPR_NEST_MAX: c_int = 7;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_LINE_MAX: c_int = 8;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_RE_DUP_MAX: c_int = 9;
+
 pub const USER_POSIX2_VERSION: c_int = 10;
 pub const USER_POSIX2_C_BIND: c_int = 11;
 pub const USER_POSIX2_C_DEV: c_int = 12;
@@ -2444,6 +2469,9 @@ pub const SO_TS_BINTIME: c_int = 1;
 pub const SO_TS_REALTIME: c_int = 2;
 pub const SO_TS_MONOTONIC: c_int = 3;
 pub const SO_TS_DEFAULT: c_int = SO_TS_REALTIME_MICRO;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SO_TS_CLOCK_MAX: c_int = SO_TS_MONOTONIC;
 
 pub const LOCAL_CREDS: c_int = 2;
@@ -2729,6 +2757,8 @@ pub const IFNET_SLOWHZ: c_int = 1;
 pub const IFAN_ARRIVAL: c_int = 0;
 pub const IFAN_DEPARTURE: c_int = 1;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const IFSTATMAX: c_int = 800;
 
 pub const RSS_FUNC_NONE: c_int = 0;
@@ -3066,6 +3096,9 @@ pub const TCP_PCAP_IN: c_int = 4096;
 pub const TCP_FUNCTION_BLK: c_int = 8192;
 pub const TCP_FUNCTION_ALIAS: c_int = 8193;
 pub const TCP_FASTOPEN_PSK_LEN: c_int = 16;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const TCP_FUNCTION_NAME_LEN_MAX: c_int = 32;
 
 pub const TCP_REUSPORT_LB_NUMA: c_int = 1026;
@@ -3432,71 +3465,111 @@ pub const KKST_STATE_SWAPPED: c_int = 1;
 pub const KKST_STATE_RUNNING: c_int = 2;
 
 // Constants about priority.
+
 pub const PRI_MIN: c_int = 0;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MAX: c_int = 255;
+
 pub const PRI_MIN_ITHD: c_int = PRI_MIN;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MAX_ITHD: c_int = PRI_MIN_REALTIME - 1;
+
 pub const PI_REALTIME: c_int = PRI_MIN_ITHD + 0;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PI_AV: c_int = PRI_MIN_ITHD + 4;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PI_NET: c_int = PRI_MIN_ITHD + 8;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PI_DISK: c_int = PRI_MIN_ITHD + 12;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PI_TTY: c_int = PRI_MIN_ITHD + 16;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PI_DULL: c_int = PRI_MIN_ITHD + 20;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PI_SOFT: c_int = PRI_MIN_ITHD + 24;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MIN_REALTIME: c_int = 48;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MAX_REALTIME: c_int = PRI_MIN_KERN - 1;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MIN_KERN: c_int = 80;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MAX_KERN: c_int = PRI_MIN_TIMESHARE - 1;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PSWP: c_int = PRI_MIN_KERN + 0;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PVM: c_int = PRI_MIN_KERN + 4;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PINOD: c_int = PRI_MIN_KERN + 8;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRIBIO: c_int = PRI_MIN_KERN + 12;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PVFS: c_int = PRI_MIN_KERN + 16;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PZERO: c_int = PRI_MIN_KERN + 20;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PSOCK: c_int = PRI_MIN_KERN + 24;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PWAIT: c_int = PRI_MIN_KERN + 28;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PLOCK: c_int = PRI_MIN_KERN + 32;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PPAUSE: c_int = PRI_MIN_KERN + 36;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PRI_MIN_TIMESHARE: c_int = 120;
+
 pub const PRI_MAX_TIMESHARE: c_int = PRI_MIN_IDLE - 1;
-#[deprecated(since = "0.2.133", note = "Not stable across OS versions")]
-#[allow(deprecated)]
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PUSER: c_int = PRI_MIN_TIMESHARE;
+
 pub const PRI_MIN_IDLE: c_int = 224;
 pub const PRI_MAX_IDLE: c_int = PRI_MAX;
 
@@ -3512,6 +3585,7 @@ cfg_if! {
         pub const ARG_MAX: c_int = 2 * 256 * 1024;
     }
 }
+
 pub const CHILD_MAX: c_int = 40;
 /// max command name remembered
 pub const MAXCOMLEN: usize = 19;
@@ -3535,10 +3609,16 @@ pub const MAXHOSTNAMELEN: c_int = 256;
 pub const MAX_CANON: c_int = 255;
 /// max bytes in terminal input
 pub const MAX_INPUT: c_int = 255;
-/// max bytes in a file name
+/// Max bytes in a file name.
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NAME_MAX: c_int = 255;
 pub const MAXSYMLINKS: c_int = 32;
-/// max supplemental group id's
+/// Max supplemental group IDs.
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NGROUPS_MAX: c_int = 1023;
 /// max open files per process
 pub const OPEN_MAX: c_int = 64;
@@ -3552,23 +3632,58 @@ pub const _POSIX_PIPE_BUF: c_int = 512;
 pub const _POSIX_SSIZE_MAX: c_int = 32767;
 pub const _POSIX_STREAM_MAX: c_int = 8;
 
-/// max ibase/obase values in bc(1)
+/// Max ibase/obase values in bc(1).
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_BASE_MAX: c_int = 99;
-/// max array elements in bc(1)
+
+/// Max array elements in bc(1).
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_DIM_MAX: c_int = 2048;
-/// max scale value in bc(1)
+
+/// Max scale value in bc(1).
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_SCALE_MAX: c_int = 99;
-/// max const string length in bc(1)
+
+/// Max const string length in bc(1).
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const BC_STRING_MAX: c_int = 1000;
-/// max character class name size
+
+/// Max character class name size.
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const CHARCLASS_NAME_MAX: c_int = 14;
-/// max weights for order keyword
+
+/// Max weights for order keyword.
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const COLL_WEIGHTS_MAX: c_int = 10;
-/// max expressions nested in expr(1)
+
+/// Max expressions nested in expr(1).
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const EXPR_NEST_MAX: c_int = 32;
-/// max bytes in an input line
+
+/// Max bytes in an input line.
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const LINE_MAX: c_int = 2048;
-/// max RE's in interval notation
+
+/// Max RE's in interval notation.
+///
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RE_DUP_MAX: c_int = 255;
 
 pub const _POSIX2_BC_BASE_MAX: c_int = 99;
@@ -3976,6 +4091,8 @@ pub const RTF_FIXEDMTU: c_int = 0x80000;
 
 pub const RTM_VERSION: c_int = 5;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTAX_MAX: c_int = 8;
 
 // sys/signal.h
@@ -4023,7 +4140,11 @@ pub const SCTP_PR_SCTP_TTL: c_int = 0x0001;
 pub const SCTP_PR_SCTP_PRIO: c_int = 0x0002;
 pub const SCTP_PR_SCTP_BUF: c_int = SCTP_PR_SCTP_PRIO;
 pub const SCTP_PR_SCTP_RTX: c_int = 0x0003;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SCTP_PR_SCTP_MAX: c_int = SCTP_PR_SCTP_RTX;
+
 pub const SCTP_PR_SCTP_ALL: c_int = 0x000f;
 
 pub const SCTP_INIT: c_int = 0x0001;
@@ -4105,6 +4226,9 @@ pub const SCTP_ASSOC_SUPPORTS_ASCONF: c_int = 0x03;
 pub const SCTP_ASSOC_SUPPORTS_MULTIBUF: c_int = 0x04;
 pub const SCTP_ASSOC_SUPPORTS_RE_CONFIG: c_int = 0x05;
 pub const SCTP_ASSOC_SUPPORTS_INTERLEAVING: c_int = 0x06;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SCTP_ASSOC_SUPPORTS_MAX: c_int = 0x06;
 
 pub const SCTP_ADDR_AVAILABLE: c_int = 0x0001;
diff --git a/src/unix/bsd/freebsdlike/mod.rs b/src/unix/bsd/freebsdlike/mod.rs
index 1ccf04eb2c85c..14b1b76203218 100644
--- a/src/unix/bsd/freebsdlike/mod.rs
+++ b/src/unix/bsd/freebsdlike/mod.rs
@@ -408,10 +408,6 @@ s! {
 // Non-public helper constant
 const SIZEOF_LONG: usize = size_of::<c_long>();
 
-#[deprecated(
-    since = "0.2.64",
-    note = "Can vary at runtime.  Use sysconf(3) instead"
-)]
 pub const AIO_LISTIO_MAX: c_int = 16;
 pub const AIO_CANCELED: c_int = 1;
 pub const AIO_NOTCANCELED: c_int = 2;
diff --git a/src/unix/bsd/mod.rs b/src/unix/bsd/mod.rs
index 47fd27321609f..586a1e05aea18 100644
--- a/src/unix/bsd/mod.rs
+++ b/src/unix/bsd/mod.rs
@@ -163,7 +163,10 @@ pub const FIOASYNC: c_ulong = 0x8004667d;
 pub const FIOSETOWN: c_ulong = 0x8004667c;
 pub const FIOGETOWN: c_ulong = 0x4004667b;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 1024;
+
 pub const MAXPATHLEN: c_int = PATH_MAX;
 
 pub const IOV_MAX: c_int = 1024;
diff --git a/src/unix/bsd/netbsdlike/netbsd/mod.rs b/src/unix/bsd/netbsdlike/netbsd/mod.rs
index 08afb94b70232..282c6cd6440a9 100644
--- a/src/unix/bsd/netbsdlike/netbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/netbsd/mod.rs
@@ -1715,6 +1715,8 @@ pub const KVME_FLAG_PAGEABLE: c_int = 0x000000008;
 pub const KVME_FLAG_GROWS_UP: c_int = 0x000000010;
 pub const KVME_FLAG_GROWS_DOWN: c_int = 0x000000020;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NGROUPS_MAX: c_int = 16;
 
 pub const KI_NGROUPS: c_int = 16;
@@ -1791,6 +1793,9 @@ pub const RTM_CHGADDR: c_int = 0x18;
 pub const RTA_TAG: c_int = 0x100;
 
 pub const RTAX_TAG: c_int = 8;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTAX_MAX: c_int = 9;
 
 // For eventfd
diff --git a/src/unix/bsd/netbsdlike/openbsd/mod.rs b/src/unix/bsd/netbsdlike/openbsd/mod.rs
index e4b3f2c509afa..5f14ed15b6e3f 100644
--- a/src/unix/bsd/netbsdlike/openbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/openbsd/mod.rs
@@ -1510,6 +1510,8 @@ pub const ISOFSMNT_EXTATT: c_int = 0x4; // enable extended attr
 pub const ISOFSMNT_NOJOLIET: c_int = 0x8; // disable Joliet Ext
 pub const ISOFSMNT_SESS: c_int = 0x10; // use iso_args.sess
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NFS_ARGSVERSION: c_int = 4; // change when nfs_args changes
 
 pub const NFSMNT_RESVPORT: c_int = 0; // always use reserved ports
@@ -1817,6 +1819,9 @@ pub const RTAX_BFD: c_int = 11;
 pub const RTAX_DNS: c_int = 12;
 pub const RTAX_STATIC: c_int = 13;
 pub const RTAX_SEARCH: c_int = 14;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTAX_MAX: c_int = 15;
 
 const fn _ALIGN(p: usize) -> usize {
diff --git a/src/unix/cygwin/mod.rs b/src/unix/cygwin/mod.rs
index f63a05e9830ef..9572b9b217e04 100644
--- a/src/unix/cygwin/mod.rs
+++ b/src/unix/cygwin/mod.rs
@@ -897,8 +897,15 @@ pub const ARG_MAX: c_int = 32000;
 pub const CHILD_MAX: c_int = 256;
 pub const IOV_MAX: c_int = 1024;
 pub const PTHREAD_STACK_MIN: size_t = 65536;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 4096;
+
 pub const PIPE_BUF: usize = 4096;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NGROUPS_MAX: c_int = 1024;
 
 pub const FILENAME_MAX: c_int = 4096;
diff --git a/src/unix/haiku/mod.rs b/src/unix/haiku/mod.rs
index eddcd302f9315..53694109f35ef 100644
--- a/src/unix/haiku/mod.rs
+++ b/src/unix/haiku/mod.rs
@@ -902,6 +902,9 @@ pub const MINSIGSTKSZ: size_t = 8192;
 pub const SIGSTKSZ: size_t = 16384;
 
 pub const IOV_MAX: c_int = 1024;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 1024;
 
 pub const SA_NOCLDSTOP: c_int = 0x01;
diff --git a/src/unix/hurd/mod.rs b/src/unix/hurd/mod.rs
index 47164e1f2b7b5..a55b0f8f5e8cc 100644
--- a/src/unix/hurd/mod.rs
+++ b/src/unix/hurd/mod.rs
@@ -1230,7 +1230,11 @@ pub const PF_IPX: c_int = 23;
 pub const PF_SIP: c_int = 24;
 pub const PF_PIP: c_int = 25;
 pub const PF_INET6: c_int = 26;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PF_MAX: c_int = 27;
+
 pub const AF_UNSPEC: c_int = 0;
 pub const AF_LOCAL: c_int = 1;
 pub const AF_UNIX: c_int = 1;
@@ -1260,7 +1264,11 @@ pub const AF_IPX: c_int = 23;
 pub const AF_SIP: c_int = 24;
 pub const pseudo_AF_PIP: c_int = 25;
 pub const AF_INET6: c_int = 26;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const AF_MAX: c_int = 27;
+
 pub const SOMAXCONN: c_int = 4096;
 pub const _SS_SIZE: usize = 128;
 pub const CMGROUP_MAX: usize = 16;
@@ -1526,8 +1534,15 @@ pub const _POSIX_QLIMIT: usize = 1;
 pub const _POSIX_HIWAT: usize = 512;
 pub const _POSIX_UIO_MAXIOV: usize = 16;
 pub const _POSIX_CLOCKRES_MIN: usize = 20000000;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NAME_MAX: usize = 255;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NGROUPS_MAX: usize = 256;
+
 pub const _POSIX_THREAD_KEYS_MAX: usize = 128;
 pub const _POSIX_THREAD_DESTRUCTOR_ITERATIONS: usize = 4;
 pub const _POSIX_THREAD_THREADS_MAX: usize = 64;
@@ -3207,6 +3222,9 @@ pub const RTLD_DI_PROFILEOUT: c_int = 8;
 pub const RTLD_DI_TLS_MODID: c_int = 9;
 pub const RTLD_DI_TLS_DATA: c_int = 10;
 pub const RTLD_DI_PHDR: c_int = 11;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RTLD_DI_MAX: c_int = 11;
 
 pub const SI_ASYNCIO: c_int = -4;
diff --git a/src/unix/linux_like/android/mod.rs b/src/unix/linux_like/android/mod.rs
index cea6778750119..ec6408ebb44fa 100644
--- a/src/unix/linux_like/android/mod.rs
+++ b/src/unix/linux_like/android/mod.rs
@@ -1681,6 +1681,9 @@ pub const NFQA_CFG_F_CONNTRACK: c_int = 0x0002;
 pub const NFQA_CFG_F_GSO: c_int = 0x0004;
 pub const NFQA_CFG_F_UID_GID: c_int = 0x0008;
 pub const NFQA_CFG_F_SECCTX: c_int = 0x0010;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NFQA_CFG_F_MAX: c_int = 0x0020;
 
 pub const NFQA_SKB_CSUMNOTREADY: c_int = 0x0001;
@@ -2001,7 +2004,11 @@ pub const NFT_REG_1: c_int = 1;
 pub const NFT_REG_2: c_int = 2;
 pub const NFT_REG_3: c_int = 3;
 pub const NFT_REG_4: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const __NFT_REG_MAX: c_int = 5;
+
 pub const NFT_REG32_00: c_int = 8;
 pub const NFT_REG32_01: c_int = 9;
 pub const NFT_REG32_02: c_int = 10;
@@ -2050,6 +2057,9 @@ pub const NFT_MSG_NEWOBJ: c_int = 18;
 pub const NFT_MSG_GETOBJ: c_int = 19;
 pub const NFT_MSG_DELOBJ: c_int = 20;
 pub const NFT_MSG_GETOBJ_RESET: c_int = 21;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NFT_MSG_MAX: c_int = 25;
 
 pub const NFT_SET_ANONYMOUS: c_int = 0x1;
@@ -2181,31 +2191,77 @@ pub const NFT_NG_INCREMENTAL: c_int = 0;
 pub const NFT_NG_RANDOM: c_int = 1;
 
 // linux/input.h
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const FF_MAX: crate::__u16 = 0x7f;
+
 pub const FF_CNT: usize = FF_MAX as usize + 1;
 
 // linux/input-event-codes.h
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const INPUT_PROP_MAX: crate::__u16 = 0x1f;
+
 pub const INPUT_PROP_CNT: usize = INPUT_PROP_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const EV_MAX: crate::__u16 = 0x1f;
+
 pub const EV_CNT: usize = EV_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SYN_MAX: crate::__u16 = 0xf;
+
 pub const SYN_CNT: usize = SYN_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const KEY_MAX: crate::__u16 = 0x2ff;
+
 pub const KEY_CNT: usize = KEY_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const REL_MAX: crate::__u16 = 0x0f;
+
 pub const REL_CNT: usize = REL_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const ABS_MAX: crate::__u16 = 0x3f;
+
 pub const ABS_CNT: usize = ABS_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SW_MAX: crate::__u16 = 0x0f;
+
 pub const SW_CNT: usize = SW_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const MSC_MAX: crate::__u16 = 0x07;
+
 pub const MSC_CNT: usize = MSC_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const LED_MAX: crate::__u16 = 0x0f;
+
 pub const LED_CNT: usize = LED_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const REP_MAX: crate::__u16 = 0x01;
+
 pub const REP_CNT: usize = REP_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SND_MAX: crate::__u16 = 0x07;
+
 pub const SND_CNT: usize = SND_MAX as usize + 1;
 
 // linux/uinput.h
@@ -2835,7 +2891,11 @@ pub const PR_SCHED_CORE_GET: c_int = 0;
 pub const PR_SCHED_CORE_CREATE: c_int = 1;
 pub const PR_SCHED_CORE_SHARE_TO: c_int = 2;
 pub const PR_SCHED_CORE_SHARE_FROM: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PR_SCHED_CORE_MAX: c_int = 4;
+
 pub const PR_SCHED_CORE_SCOPE_THREAD: c_int = 0;
 pub const PR_SCHED_CORE_SCOPE_THREAD_GROUP: c_int = 1;
 pub const PR_SCHED_CORE_SCOPE_PROCESS_GROUP: c_int = 2;
@@ -3137,7 +3197,11 @@ pub const KERN_S390_USER_DEBUG_LOGGING: c_int = 51;
 pub const KERN_CORE_USES_PID: c_int = 52;
 pub const KERN_TAINTED: c_int = 53;
 pub const KERN_CADPID: c_int = 54;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const KERN_PIDMAX: c_int = 55;
+
 pub const KERN_CORE_PATTERN: c_int = 56;
 pub const KERN_PANIC_ON_OOPS: c_int = 57;
 pub const KERN_HPPA_PWRSW: c_int = 58;
@@ -3145,7 +3209,11 @@ pub const KERN_HPPA_UNALIGNED: c_int = 59;
 pub const KERN_PRINTK_RATELIMIT: c_int = 60;
 pub const KERN_PRINTK_RATELIMIT_BURST: c_int = 61;
 pub const KERN_PTY: c_int = 62;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const KERN_NGROUPS_MAX: c_int = 63;
+
 pub const KERN_SPARC_SCONS_PWROFF: c_int = 64;
 pub const KERN_HZ_TIMER: c_int = 65;
 pub const KERN_UNKNOWN_NMI_PANIC: c_int = 66;
diff --git a/src/unix/linux_like/linux/mod.rs b/src/unix/linux_like/linux/mod.rs
index 20ddce4860e97..11281dab33e40 100644
--- a/src/unix/linux_like/linux/mod.rs
+++ b/src/unix/linux_like/linux/mod.rs
@@ -1493,7 +1493,11 @@ pub const SKF_AD_VLAN_TAG_PRESENT: c_int = 48;
 pub const SKF_AD_PAY_OFFSET: c_int = 52;
 pub const SKF_AD_RANDOM: c_int = 56;
 pub const SKF_AD_VLAN_TPID: c_int = 60;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SKF_AD_MAX: c_int = 64;
+
 pub const SKF_NET_OFF: c_int = -0x100000;
 pub const SKF_LL_OFF: c_int = -0x200000;
 pub const BPF_NET_OFF: c_int = SKF_NET_OFF;
@@ -1794,6 +1798,9 @@ pub const NFQA_CFG_F_CONNTRACK: c_int = 0x0002;
 pub const NFQA_CFG_F_GSO: c_int = 0x0004;
 pub const NFQA_CFG_F_UID_GID: c_int = 0x0008;
 pub const NFQA_CFG_F_SECCTX: c_int = 0x0010;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NFQA_CFG_F_MAX: c_int = 0x0020;
 
 pub const NFQA_SKB_CSUMNOTREADY: c_int = 0x0001;
@@ -2841,7 +2848,11 @@ pub const NFT_REG_1: c_int = 1;
 pub const NFT_REG_2: c_int = 2;
 pub const NFT_REG_3: c_int = 3;
 pub const NFT_REG_4: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const __NFT_REG_MAX: c_int = 5;
+
 pub const NFT_REG32_00: c_int = 8;
 pub const NFT_REG32_01: c_int = 9;
 pub const NFT_REG32_02: c_int = 10;
@@ -2895,6 +2906,8 @@ cfg_if! {
     }
 }
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NFT_MSG_MAX: c_int = 34;
 
 pub const NFT_SET_ANONYMOUS: c_int = 0x1;
@@ -3025,7 +3038,10 @@ pub const NFT_NG_INCREMENTAL: c_int = 0;
 pub const NFT_NG_RANDOM: c_int = 1;
 
 // linux/input.h
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const FF_MAX: __u16 = 0x7f;
+
 pub const FF_CNT: usize = FF_MAX as usize + 1;
 
 // linux/input-event-codes.h
@@ -3036,27 +3052,71 @@ pub const INPUT_PROP_SEMI_MT: __u16 = 0x03;
 pub const INPUT_PROP_TOPBUTTONPAD: __u16 = 0x04;
 pub const INPUT_PROP_POINTING_STICK: __u16 = 0x05;
 pub const INPUT_PROP_ACCELEROMETER: __u16 = 0x06;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const INPUT_PROP_MAX: __u16 = 0x1f;
+
 pub const INPUT_PROP_CNT: usize = INPUT_PROP_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const EV_MAX: __u16 = 0x1f;
+
 pub const EV_CNT: usize = EV_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SYN_MAX: __u16 = 0xf;
+
 pub const SYN_CNT: usize = SYN_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const KEY_MAX: __u16 = 0x2ff;
+
 pub const KEY_CNT: usize = KEY_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const REL_MAX: __u16 = 0x0f;
+
 pub const REL_CNT: usize = REL_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const ABS_MAX: __u16 = 0x3f;
+
 pub const ABS_CNT: usize = ABS_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SW_MAX: __u16 = 0x10;
+
 pub const SW_CNT: usize = SW_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const MSC_MAX: __u16 = 0x07;
+
 pub const MSC_CNT: usize = MSC_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const LED_MAX: __u16 = 0x0f;
+
 pub const LED_CNT: usize = LED_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const REP_MAX: __u16 = 0x01;
+
 pub const REP_CNT: usize = REP_MAX as usize + 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SND_MAX: __u16 = 0x07;
+
 pub const SND_CNT: usize = SND_MAX as usize + 1;
 
 // linux/uinput.h
@@ -3290,7 +3350,11 @@ pub const SCTP_PR_SCTP_NONE: c_int = 0x0000;
 pub const SCTP_PR_SCTP_TTL: c_int = 0x0010;
 pub const SCTP_PR_SCTP_RTX: c_int = 0x0020;
 pub const SCTP_PR_SCTP_PRIO: c_int = 0x0030;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SCTP_PR_SCTP_MAX: c_int = SCTP_PR_SCTP_PRIO;
+
 pub const SCTP_PR_SCTP_MASK: c_int = 0x0030;
 pub const SCTP_ENABLE_RESET_STREAM_REQ: c_int = 0x01;
 pub const SCTP_ENABLE_RESET_ASSOC_REQ: c_int = 0x02;
@@ -3398,7 +3462,11 @@ pub const KERN_S390_USER_DEBUG_LOGGING: c_int = 51;
 pub const KERN_CORE_USES_PID: c_int = 52;
 pub const KERN_TAINTED: c_int = 53;
 pub const KERN_CADPID: c_int = 54;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const KERN_PIDMAX: c_int = 55;
+
 pub const KERN_CORE_PATTERN: c_int = 56;
 pub const KERN_PANIC_ON_OOPS: c_int = 57;
 pub const KERN_HPPA_PWRSW: c_int = 58;
@@ -3406,7 +3474,11 @@ pub const KERN_HPPA_UNALIGNED: c_int = 59;
 pub const KERN_PRINTK_RATELIMIT: c_int = 60;
 pub const KERN_PRINTK_RATELIMIT_BURST: c_int = 61;
 pub const KERN_PTY: c_int = 62;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const KERN_NGROUPS_MAX: c_int = 63;
+
 pub const KERN_SPARC_SCONS_PWROFF: c_int = 64;
 pub const KERN_HZ_TIMER: c_int = 65;
 pub const KERN_UNKNOWN_NMI_PANIC: c_int = 66;
diff --git a/src/unix/linux_like/linux/musl/b32/hexagon.rs b/src/unix/linux_like/linux/musl/b32/hexagon.rs
index 9a62e4d57d6da..307cba3fa927d 100644
--- a/src/unix/linux_like/linux/musl/b32/hexagon.rs
+++ b/src/unix/linux_like/linux/musl/b32/hexagon.rs
@@ -103,7 +103,11 @@ s! {
 
 pub const AF_FILE: c_int = 1;
 pub const AF_KCM: c_int = 41;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const AF_MAX: c_int = 43;
+
 pub const AF_QIPCRTR: c_int = 42;
 pub const EADDRINUSE: c_int = 98;
 pub const EADDRNOTAVAIL: c_int = 99;
@@ -236,7 +240,11 @@ pub const O_SYNC: c_int = 1052672;
 pub const O_RSYNC: c_int = 1052672;
 pub const PF_FILE: c_int = 1;
 pub const PF_KCM: c_int = 41;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PF_MAX: c_int = 43;
+
 pub const PF_QIPCRTR: c_int = 42;
 pub const SA_ONSTACK: c_int = 0x08000000;
 pub const SA_SIGINFO: c_int = 0x00000004;
diff --git a/src/unix/linux_like/linux_l4re_shared.rs b/src/unix/linux_like/linux_l4re_shared.rs
index d50efafa0e777..7bf5ac3e3b3a8 100644
--- a/src/unix/linux_like/linux_l4re_shared.rs
+++ b/src/unix/linux_like/linux_l4re_shared.rs
@@ -1160,7 +1160,11 @@ pub const PR_SCHED_CORE_GET: c_int = 0;
 pub const PR_SCHED_CORE_CREATE: c_int = 1;
 pub const PR_SCHED_CORE_SHARE_TO: c_int = 2;
 pub const PR_SCHED_CORE_SHARE_FROM: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PR_SCHED_CORE_MAX: c_int = 4;
+
 pub const PR_SCHED_CORE_SCOPE_THREAD: c_int = 0;
 pub const PR_SCHED_CORE_SCOPE_THREAD_GROUP: c_int = 1;
 pub const PR_SCHED_CORE_SCOPE_PROCESS_GROUP: c_int = 2;
@@ -1313,6 +1317,9 @@ pub const RT_CLASS_UNSPEC: u8 = 0;
 pub const RT_CLASS_DEFAULT: u8 = 253;
 pub const RT_CLASS_MAIN: u8 = 254;
 pub const RT_CLASS_LOCAL: u8 = 255;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const RT_CLASS_MAX: u8 = 255;
 
 pub const MAX_ADDR_LEN: usize = 7;
diff --git a/src/unix/linux_like/mod.rs b/src/unix/linux_like/mod.rs
index fd2bb96bc9283..9132061ee5528 100644
--- a/src/unix/linux_like/mod.rs
+++ b/src/unix/linux_like/mod.rs
@@ -1043,7 +1043,12 @@ pub const LOCK_UN: c_int = 8;
 pub const SS_ONSTACK: c_int = 1;
 pub const SS_DISABLE: c_int = 2;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const NAME_MAX: c_int = 255;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 4096;
 
 pub const UIO_MAXIOV: c_int = 1024;
diff --git a/src/unix/newlib/horizon/mod.rs b/src/unix/newlib/horizon/mod.rs
index 1f27bbee8d1bc..4d86a89687ee6 100644
--- a/src/unix/newlib/horizon/mod.rs
+++ b/src/unix/newlib/horizon/mod.rs
@@ -151,6 +151,9 @@ pub const EAI_SYSTEM: c_int = 11;
 pub const EAI_BADHINTS: c_int = 12;
 pub const EAI_PROTOCOL: c_int = 13;
 pub const EAI_OVERFLOW: c_int = 14;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const EAI_MAX: c_int = 15;
 
 pub const AF_UNIX: c_int = 1;
diff --git a/src/unix/newlib/rtems/mod.rs b/src/unix/newlib/rtems/mod.rs
index ec4534e32a11f..48a5ac141df96 100644
--- a/src/unix/newlib/rtems/mod.rs
+++ b/src/unix/newlib/rtems/mod.rs
@@ -56,7 +56,11 @@ pub const SIGWINCH: c_int = 24;
 pub const SIGUSR1: c_int = 25;
 pub const SIGUSR2: c_int = 26;
 pub const SIGRTMIN: c_int = 27;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const SIGRTMAX: c_int = 31;
+
 pub const SIGXCPU: c_int = 24;
 pub const SIGXFSZ: c_int = 25;
 pub const SIGVTALRM: c_int = 26;
diff --git a/src/unix/nto/mod.rs b/src/unix/nto/mod.rs
index 7ebfc2194bfb0..7865984b91da8 100644
--- a/src/unix/nto/mod.rs
+++ b/src/unix/nto/mod.rs
@@ -1154,6 +1154,8 @@ pub const LOCK_UN: c_int = 0x8;
 pub const SS_ONSTACK: c_int = 1;
 pub const SS_DISABLE: c_int = 2;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 1024;
 
 pub const UIO_MAXIOV: c_int = 1024;
@@ -2340,14 +2342,39 @@ pub const TIOCSTOP: c_int = 29807;
 pub const TIOCSWINSZ: c_int = -2146929561;
 
 pub const USER_CS_PATH: c_int = 1;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_BASE_MAX: c_int = 2;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_DIM_MAX: c_int = 3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_SCALE_MAX: c_int = 4;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_BC_STRING_MAX: c_int = 5;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_COLL_WEIGHTS_MAX: c_int = 6;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_EXPR_NEST_MAX: c_int = 7;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_LINE_MAX: c_int = 8;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const USER_RE_DUP_MAX: c_int = 9;
+
 pub const USER_POSIX2_VERSION: c_int = 10;
 pub const USER_POSIX2_C_BIND: c_int = 11;
 pub const USER_POSIX2_C_DEV: c_int = 12;
diff --git a/src/unix/redox/mod.rs b/src/unix/redox/mod.rs
index 797de99668153..8d5b7b0c36d88 100644
--- a/src/unix/redox/mod.rs
+++ b/src/unix/redox/mod.rs
@@ -333,6 +333,8 @@ cfg_if! {
 }
 
 // limits.h
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 4096;
 
 // fcntl.h
diff --git a/src/unix/solarish/illumos.rs b/src/unix/solarish/illumos.rs
index b31c31bd1f6c8..7069d8e737656 100644
--- a/src/unix/solarish/illumos.rs
+++ b/src/unix/solarish/illumos.rs
@@ -109,7 +109,11 @@ pub const FD_CLOFORK: c_int = 2;
 pub const FIL_ATTACH: c_int = 0x1;
 pub const FIL_DETACH: c_int = 0x2;
 pub const FIL_LIST: c_int = 0x3;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const FILNAME_MAX: c_int = 32;
+
 pub const FILF_PROG: c_int = 0x1;
 pub const FILF_AUTO: c_int = 0x2;
 pub const FILF_BYPASS: c_int = 0x4;
diff --git a/src/unix/solarish/mod.rs b/src/unix/solarish/mod.rs
index 5dcafd92e23b7..aa83656ab58de 100644
--- a/src/unix/solarish/mod.rs
+++ b/src/unix/solarish/mod.rs
@@ -823,6 +823,8 @@ pub const NOEXPR: crate::nl_item = 57;
 pub const _DATE_FMT: crate::nl_item = 58;
 pub const MAXSTRMSG: crate::nl_item = 58;
 
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = 1024;
 
 pub const SA_ONSTACK: c_int = 0x00000001;
diff --git a/src/vxworks/mod.rs b/src/vxworks/mod.rs
index a5f5c6908960c..d7246bcaf75f9 100644
--- a/src/vxworks/mod.rs
+++ b/src/vxworks/mod.rs
@@ -702,6 +702,9 @@ pub const PTHREAD_MUTEX_ERRORCHECK: c_int = 1;
 pub const PTHREAD_MUTEX_RECURSIVE: c_int = 2;
 pub const PTHREAD_MUTEX_DEFAULT: c_int = PTHREAD_MUTEX_NORMAL;
 pub const PTHREAD_STACK_MIN: usize = 4096;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const _PTHREAD_SHARED_SEM_NAME_MAX: usize = 30;
 
 //sched.h
@@ -1041,6 +1044,9 @@ pub const AF_SOCKDEV: c_int = 31;
 pub const AF_TIPC: c_int = 33;
 pub const AF_MIPC: c_int = 34;
 pub const AF_MIPC_SAFE: c_int = 35;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const AF_MAX: c_int = 39;
 
 // termios.h
@@ -1171,7 +1177,10 @@ pub const FIOGETNAME: c_int = 18;
 pub const FIONBIO: c_int = 0x90040010;
 
 // limits.h
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const PATH_MAX: c_int = _PARM_PATH_MAX;
+
 pub const _POSIX_PATH_MAX: c_int = 256;
 
 // Some poll stuff
@@ -1315,7 +1324,12 @@ pub const AT_REMOVEDIR: c_int = 0x200;
 pub const AT_SYMLINK_FOLLOW: c_int = 0x400;
 
 // vxParams.h definitions
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const _PARM_NAME_MAX: c_int = 255;
+
+/// This symbol is prone to change across releases upstream.
+/// See the [usage guidelines](crate#usage-guidelines) for details.
 pub const _PARM_PATH_MAX: c_int = 1024;
 
 // WAIT STUFF