[PATCH 0/1] MR4996: ntdll: Assume process-private futexes are always present on Linux.

[Brendan Shanks (＠bshanks)]

This bumps the minimum Linux kernel requirement to 2.6.22 (released in July 2007).

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/4996

[PATCH 1/1] ntdll: Assume process-private futexes are always present on Linux.

[Brendan Shanks]

From: Brendan Shanks <bshanks(a)codeweavers.com>

---
 README.md              |  2 +-
 dlls/ntdll/unix/sync.c | 52 ++++++++++--------------------------------
 2 files changed, 13 insertions(+), 41 deletions(-)

diff --git a/README.md b/README.md
index 888e95895e2..8a804b30dfc 100644
--- a/README.md
+++ b/README.md
@@ -42,7 +42,7 @@ especially the wealth of information found at https://www.winehq.org.
 
 To compile and run Wine, you must have one of the following:
 
-- Linux version 2.0.36 or later
+- Linux version 2.6.22 or later
 - FreeBSD 12.4 or later
 - Solaris x86 9 or later
 - NetBSD-current
diff --git a/dlls/ntdll/unix/sync.c b/dlls/ntdll/unix/sync.c
index bfbcaf4a851..c73110f0ae6 100644
--- a/dlls/ntdll/unix/sync.c
+++ b/dlls/ntdll/unix/sync.c
@@ -103,10 +103,7 @@ static inline ULONGLONG monotonic_counter(void)
 
 #ifdef __linux__
 
-#define FUTEX_WAIT 0
-#define FUTEX_WAKE 1
-
-static int futex_private = 128;
+#include <linux/futex.h>
 
 static inline int futex_wait( const LONG *addr, int val, struct timespec *timeout )
 {
@@ -118,32 +115,15 @@ static inline int futex_wait( const LONG *addr, int val, struct timespec *timeou
             long tv_nsec;
         } timeout32 = { timeout->tv_sec, timeout->tv_nsec };
 
-        return syscall( __NR_futex, addr, FUTEX_WAIT | futex_private, val, &timeout32, 0, 0 );
+        return syscall( __NR_futex, addr, FUTEX_WAIT_PRIVATE, val, &timeout32, 0, 0 );
     }
 #endif
-    return syscall( __NR_futex, addr, FUTEX_WAIT | futex_private, val, timeout, 0, 0 );
+    return syscall( __NR_futex, addr, FUTEX_WAIT_PRIVATE, val, timeout, 0, 0 );
 }
 
 static inline int futex_wake( const LONG *addr, int val )
 {
-    return syscall( __NR_futex, addr, FUTEX_WAKE | futex_private, val, NULL, 0, 0 );
-}
-
-static inline int use_futexes(void)
-{
-    static LONG supported = -1;
-
-    if (supported == -1)
-    {
-        futex_wait( &supported, 10, NULL );
-        if (errno == ENOSYS)
-        {
-            futex_private = 0;
-            futex_wait( &supported, 10, NULL );
-        }
-        supported = (errno != ENOSYS);
-    }
-    return supported;
+    return syscall( __NR_futex, addr, FUTEX_WAKE_PRIVATE, val, NULL, 0, 0 );
 }
 
 #endif
@@ -2356,11 +2336,10 @@ union tid_alert_entry
 {
 #ifdef HAVE_KQUEUE
     int kq;
+#elif defined(__linux__)
+    LONG futex;
 #else
     HANDLE event;
-#ifdef __linux__
-    LONG futex;
-#endif
 #endif
 };
 
@@ -2426,12 +2405,9 @@ static union tid_alert_entry *get_tid_alert_entry( HANDLE tid )
         if (InterlockedCompareExchange( (LONG *)&entry->kq, kq, 0 ))
             close( kq );
     }
+#elif defined(__linux__)
+    return entry;
 #else
-#ifdef __linux__
-    if (use_futexes())
-        return entry;
-#endif
-
     if (!entry->event)
     {
         HANDLE event;
@@ -2473,17 +2449,14 @@ NTSTATUS WINAPI NtAlertThreadByThreadId( HANDLE tid )
         kevent( entry->kq, &signal_event, 1, NULL, 0, NULL );
         return STATUS_SUCCESS;
     }
-#else
-#ifdef __linux__
-    if (use_futexes())
+#elif defined(__linux__)
     {
         LONG *futex = &entry->futex;
         if (!InterlockedExchange( futex, 1 ))
             futex_wake( futex, 1 );
         return STATUS_SUCCESS;
     }
-#endif
-
+#else
     return NtSetEvent( entry->event, NULL );
 #endif
 }
@@ -2578,7 +2551,6 @@ NTSTATUS WINAPI NtWaitForAlertByThreadId( const void *address, const LARGE_INTEG
     if (!entry) return STATUS_INVALID_CID;
 
 #ifdef __linux__
-    if (use_futexes())
     {
         LONG *futex = &entry->futex;
         ULONGLONG end;
@@ -2610,11 +2582,11 @@ NTSTATUS WINAPI NtWaitForAlertByThreadId( const void *address, const LARGE_INTEG
         }
         return STATUS_ALERTED;
     }
-#endif
-
+#else
     status = NtWaitForSingleObject( entry->event, FALSE, timeout );
     if (!status) return STATUS_ALERTED;
     return status;
+#endif
 }
 
 #endif
-- 
GitLab

https://gitlab.winehq.org/wine/wine/-/merge_requests/4996