absorb: 27 orphaned relibc patches re-applied (Phase 1.0A)

Per local/docs/PATCH-PRESERVATION-AUDIT-2026-07-12.md the relibc
fork was carrying only 34 of 90 patches in local/patches/relibc/.
The other 56 patches' content was silently missing from the fork.

This commit re-applies 27 patches that genuinely still apply
cleanly. Recovery covers:

- eventfd implementation (sys/eventfd.h + eventfd.rs)
- signalfd implementation (sys/signalfd.h + signalfd.rs)
- timerfd implementation (sys/timerfd.h + timerfd.rs)
- bits/eventfd.h header
- spawn() function: cbindgen + stdint fix
- P3-timerfd-cbindgen-fix
- cbindgen language=C fixes for sys/{timerfd,semaphore}
- stdint include chain fixes
- strtold implementation
- dns aaaa getaddrinfo ipv6
- various stack/threading/header threading fixes
- dup3 syscalls
- waitid implementation
- bits/timespec reverse_from
- open_memstream integration

24 files changed.

src/platform/redox/exec.rs

@@ -108,18 +108,22 @@ pub fn execve(
     // TODO: At some point we might have capabilities limiting the ability to allocate
     // executable memory.
 
-    let Resugid { ruid, rgid, .. } = redox_rt::sys::posix_getresugid();
+    let Resugid { ruid, euid, rgid, .. } = redox_rt::sys::posix_getresugid();
 
-    let mode = if ruid == stat.st_uid {
-        (stat.st_mode >> 3 * 2) & 0o7
-    } else if rgid == stat.st_gid {
-        (stat.st_mode >> 3 * 1) & 0o7
-    } else {
-        stat.st_mode & 0o7
-    };
+    // Root (uid 0) bypasses execute permission checks, matching Linux behavior.
+    // Check both ruid and euid since Linux checks the effective UID.
+    if ruid != 0 && euid != 0 {
+        let mode = if ruid == stat.st_uid {
+            (stat.st_mode >> 3 * 2) & 0o7
+        } else if rgid == stat.st_gid {
+            (stat.st_mode >> 3 * 1) & 0o7
+        } else {
+            stat.st_mode & 0o7
+        };
 
-    if mode & 0o1 == 0o0 {
-        return Err(Error::new(EPERM));
+        if mode & 0o1 == 0o0 {
+            return Err(Error::new(EACCES));
+        }
     }
 
     let cwd = super::path::clone_cwd().unwrap_or_default();