musl: fix utmpx struct layout

This ut_session has changed from long to int + padding in newer
versions. This was already reflected on loongarch64 and ohos - this
commit adds this change, and re-enables the test when musl_v1_2_3 is
set.

Co-authored-by: Ariadne Conill <ariadne@dereferenced.org>

(backport <rust-lang#4443>)
(cherry picked from commit 1038c7f)

Author: xbjfk

libc-test/build.rs

@@ -4897,8 +4897,8 @@ fn test_linux(target: &str) {
         (struct_ == "statvfs64" && field == "__f_spare") ||
         // the `xsk_tx_metadata_union` field is an anonymous union
         (struct_ == "xsk_tx_metadata" && field == "xsk_tx_metadata_union") ||
-        // FIXME(musl): After musl 1.2.0, the type becomes `int` instead of `long`.
-        (struct_ == "utmpx" && field == "ut_session")
+        // After musl 1.2.0, the type becomes `int` instead of `long`.
+        (old_musl && struct_ == "utmpx" && field == "ut_session")
     });
 
     cfg.skip_roundtrip(move |s| match s {

src/unix/linux_like/linux/musl/mod.rs

@@ -438,13 +438,6 @@ s_no_extra_traits! {
         pub __reserved: [c_char; 256],
     }
 
-    // FIXME(musl): musl added paddings and adjusted
-    // layout in 1.2.0 but our CI is still 1.1.24.
-    // So, I'm leaving some fields as cfg for now.
-    // ref. https://github.com/bminor/musl/commit/
-    // 1e7f0fcd7ff2096904fd93a2ee6d12a2392be392
-    //
-    // OpenHarmony uses the musl 1.2 layout.
     pub struct utmpx {
         pub ut_type: c_short,
         __ut_pad1: c_short,
@@ -455,31 +448,24 @@ s_no_extra_traits! {
         pub ut_host: [c_char; 256],
         pub ut_exit: __exit_status,
 
-        #[cfg(target_env = "musl")]
-        #[cfg(not(target_arch = "loongarch64"))]
+        #[cfg(not(musl_v1_2_3))]
+        #[deprecated(
+            since = "0.2.173",
+            note = "The ABI of this field has changed from c_long to c_int with padding, \
+                we'll follow that change in the future release. See #4443 for more info."
+        )]
         pub ut_session: c_long,
 
-        #[cfg(target_env = "musl")]
-        #[cfg(target_arch = "loongarch64")]
-        pub ut_session: c_int,
-
-        #[cfg(target_env = "musl")]
-        #[cfg(target_arch = "loongarch64")]
+        #[cfg(musl_v1_2_3)]
+        #[cfg(not(target_endian = "little"))]
         __ut_pad2: c_int,
 
-        #[cfg(target_env = "ohos")]
-        #[cfg(target_endian = "little")]
+        #[cfg(musl_v1_2_3)]
         pub ut_session: c_int,
-        #[cfg(target_env = "ohos")]
-        #[cfg(target_endian = "little")]
-        __ut_pad2: c_int,
 
-        #[cfg(target_env = "ohos")]
-        #[cfg(not(target_endian = "little"))]
+        #[cfg(musl_v1_2_3)]
+        #[cfg(target_endian = "little")]
         __ut_pad2: c_int,
-        #[cfg(target_env = "ohos")]
-        #[cfg(not(target_endian = "little"))]
-        pub ut_session: c_int,
 
         pub ut_tv: crate::timeval,
         pub ut_addr_v6: [c_uint; 4],
@@ -555,6 +541,7 @@ cfg_if! {
         }
 
         impl PartialEq for utmpx {
+            #[allow(deprecated)]
             fn eq(&self, other: &utmpx) -> bool {
                 self.ut_type == other.ut_type
                     //&& self.__ut_pad1 == other.__ut_pad1
@@ -579,6 +566,7 @@ cfg_if! {
         impl Eq for utmpx {}
 
         impl fmt::Debug for utmpx {
+            #[allow(deprecated)]
             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                 f.debug_struct("utmpx")
                     .field("ut_type", &self.ut_type)
@@ -599,6 +587,7 @@ cfg_if! {
         }
 
         impl hash::Hash for utmpx {
+            #[allow(deprecated)]
             fn hash<H: hash::Hasher>(&self, state: &mut H) {
                 self.ut_type.hash(state);
                 //self.__ut_pad1.hash(state);