Auto merge of #3937 - FrankReh:syscall-eventfd2, r=RalfJung

syscall eventfd2

Add plumbing so syscall of SYS_eventfd2 can take advantage of the eventfd support already built into Miri.

src/tools/miri/src/shims/unix/linux/foreign_items.rs

@@ -122,6 +122,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
                 let sys_getrandom = this.eval_libc("SYS_getrandom").to_target_usize(this)?;
                 let sys_futex = this.eval_libc("SYS_futex").to_target_usize(this)?;
+                let sys_eventfd2 = this.eval_libc("SYS_eventfd2").to_target_usize(this)?;
 
                 if args.is_empty() {
                     throw_ub_format!(
@@ -155,6 +156,17 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     id if id == sys_futex => {
                         futex(this, &args[1..], dest)?;
                     }
+                    id if id == sys_eventfd2 => {
+                        let [_, initval, flags, ..] = args else {
+                            throw_ub_format!(
+                                "incorrect number of arguments for `eventfd2` syscall: got {}, expected at least 3",
+                                args.len()
+                            );
+                        };
+
+                        let result = this.eventfd(initval, flags)?;
+                        this.write_int(result.to_i32()?, dest)?;
+                    }
                     id => {
                         this.handle_unsupported_foreign_item(format!(
                             "can't execute syscall with ID {id}"

src/tools/miri/tests/pass-dep/libc/libc-eventfd.rs

@@ -10,6 +10,7 @@ use std::thread;
 fn main() {
     test_read_write();
     test_race();
+    test_syscall();
 }
 
 fn read_bytes<const N: usize>(fd: i32, buf: &mut [u8; N]) -> i32 {
@@ -109,3 +110,11 @@ fn test_race() {
     thread::yield_now();
     thread1.join().unwrap();
 }
+
+// This is a test for calling eventfd2 through a syscall.
+fn test_syscall() {
+    let initval = 0 as libc::c_uint;
+    let flags = (libc::EFD_CLOEXEC | libc::EFD_NONBLOCK) as libc::c_int;
+    let fd = unsafe { libc::syscall(libc::SYS_eventfd2, initval, flags) };
+    assert_ne!(fd, -1);
+}