From 715d808f14e132df9eb4e29261d010eca5cfb82a Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Sat, 11 May 2019 10:33:41 +0200
Subject: [PATCH] linux: Fix clock_gettime on systems w/o VDSO

---
 std/os/linux.zig | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/std/os/linux.zig b/std/os/linux.zig
index 99a29db58..3b0d0cc10 100644
--- a/std/os/linux.zig
+++ b/std/os/linux.zig
@@ -959,10 +959,13 @@ pub fn waitpid(pid: i32, status: *i32, options: i32) usize {
     return syscall4(SYS_wait4, @bitCast(usize, isize(pid)), @ptrToInt(status), @bitCast(usize, isize(options)), 0);
 }
 
+var vdso_clock_gettime = @ptrCast(?*const c_void, init_vdso_clock_gettime);
+
 pub fn clock_gettime(clk_id: i32, tp: *timespec) usize {
     if (VDSO_CGT_SYM.len != 0) {
-        const f = @atomicLoad(@typeOf(init_vdso_clock_gettime), &vdso_clock_gettime, builtin.AtomicOrder.Unordered);
-        if (@ptrToInt(f) != 0) {
+        const ptr = @atomicLoad(?*const c_void, &vdso_clock_gettime, .Unordered);
+        if (ptr) |fn_ptr| {
+            const f = @ptrCast(@typeOf(clock_gettime), fn_ptr);
             const rc = f(clk_id, tp);
             switch (rc) {
                 0, @bitCast(usize, isize(-EINVAL)) => return rc,
@@ -972,13 +975,18 @@ pub fn clock_gettime(clk_id: i32, tp: *timespec) usize {
     }
     return syscall2(SYS_clock_gettime, @bitCast(usize, isize(clk_id)), @ptrToInt(tp));
 }
-var vdso_clock_gettime = init_vdso_clock_gettime;
+
 extern fn init_vdso_clock_gettime(clk: i32, ts: *timespec) usize {
-    const addr = vdso.lookup(VDSO_CGT_VER, VDSO_CGT_SYM);
-    var f = @intToPtr(@typeOf(init_vdso_clock_gettime), addr);
-    _ = @cmpxchgStrong(@typeOf(init_vdso_clock_gettime), &vdso_clock_gettime, init_vdso_clock_gettime, f, builtin.AtomicOrder.Monotonic, builtin.AtomicOrder.Monotonic);
-    if (@ptrToInt(f) == 0) return @bitCast(usize, isize(-ENOSYS));
-    return f(clk, ts);
+    const ptr = @intToPtr(?*const c_void, vdso.lookup(VDSO_CGT_VER, VDSO_CGT_SYM));
+    // Note that we may not have a VDSO at all, update the stub address anyway
+    // so that clock_gettime will fall back on the good old (and slow) syscall
+    _ = @cmpxchgStrong(?*const c_void, &vdso_clock_gettime, &init_vdso_clock_gettime, ptr, .Monotonic, .Monotonic);
+    // Call into the VDSO if available
+    if (ptr) |fn_ptr| {
+        const f = @ptrCast(@typeOf(clock_gettime), fn_ptr);
+        return f(clk, ts);
+    }
+    return @bitCast(usize, isize(-ENOSYS));
 }
 
 pub fn clock_getres(clk_id: i32, tp: *timespec) usize {