Commit 5a142dfa56

@@ -372,4 +372,54 @@ pub fn addCases(ctx: *TestContext) !void {
             \\pub export fn main() void { _ = entry; }
         );
     }
+
+    {
+        var case = ctx.exeUsingLlvmBackend("f segment address space reading and writing", linux_x64);
+        case.addCompareOutput(
+            \\fn assert(ok: bool) void {
+            \\    if (!ok) unreachable;
+            \\}
+            \\
+            \\fn setFs(value: c_ulong) void {
+            \\    asm volatile (
+            \\        \\syscall
+            \\        :
+            \\        : [number] "{rax}" (158),
+            \\          [code] "{rdi}" (0x1002),
+            \\          [val] "{rsi}" (value),
+            \\        : "rcx", "r11", "memory"
+            \\    );
+            \\}
+            \\
+            \\fn getFs() c_ulong {
+            \\    var result: c_ulong = undefined;
+            \\    asm volatile (
+            \\        \\syscall
+            \\        :
+            \\        : [number] "{rax}" (158),
+            \\          [code] "{rdi}" (0x1003),
+            \\          [ptr] "{rsi}" (@ptrToInt(&result)),
+            \\        : "rcx", "r11", "memory"
+            \\    );
+            \\    return result;
+            \\}
+            \\
+            \\var test_value: u64 = 12345;
+            \\
+            \\pub export fn main() c_int {
+            \\    const orig_fs = getFs();
+            \\
+            \\    setFs(@ptrToInt(&test_value));
+            \\    assert(getFs() == @ptrToInt(&test_value));
+            \\
+            \\    var test_ptr = @intToPtr(*allowzero addrspace(.fs) u64, 0);
+            \\    assert(test_ptr.* == 12345);
+            \\    test_ptr.* = 98765;
+            \\    assert(test_value == 98765);
+            \\
+            \\    setFs(orig_fs);
+            \\    return 0;
+            \\}
+        , "");
+    }
 }