Add sched_yield syscall

src/Enclave.edl

@@ -21,6 +21,7 @@ enclave {
         void ocall_clock_gettime(int clockid, [out] long* sec, [out] long* ns);
         void ocall_nanosleep(long sec, long nsec);
         void ocall_sync(void);
+        void ocall_sched_yield(void);
         int ocall_sched_getaffinity([out] int *error, int pid, size_t cpusize, [out, size=cpusize] unsigned char* buf);
         int ocall_sched_setaffinity([out] int *error, int pid, size_t cpusize, [in, size=cpusize] const unsigned char* buf);
     };

src/libos/src/process/mod.rs

@@ -3,7 +3,7 @@ pub use self::exit::{do_exit, do_wait4, ChildProcessFilter};
 pub use self::futex::{futex_op_and_flags_from_u32, futex_wait, futex_wake, FutexFlags, FutexOp};
 pub use self::process::{Status, IDLE_PROCESS};
 pub use self::process_table::get;
-pub use self::sched::{do_sched_getaffinity, do_sched_setaffinity, CpuSet};
+pub use self::sched::{do_sched_getaffinity, do_sched_setaffinity, do_sched_yield, CpuSet};
 pub use self::spawn::{do_spawn, ElfFile, FileAction, ProgramHeaderExt};
 pub use self::task::{current_pid, get_current, run_task};
 pub use self::thread::{do_clone, do_set_tid_address, CloneFlags, ThreadGroup};

src/libos/src/process/sched.rs

@@ -15,6 +15,7 @@ extern "C" {
         cpusetsize: size_t,
         mask: *const c_uchar,
     ) -> sgx_status_t;
+    fn ocall_sched_yield() -> sgx_status_t;
 }
 
 pub struct CpuSet {
@@ -122,3 +123,10 @@ pub fn do_sched_setaffinity(pid: pid_t, cpu_set: &CpuSet) -> Result<i32> {
     }
     Ok(ret)
 }
+
+pub fn do_sched_yield() {
+    unsafe {
+        let status = ocall_sched_yield();
+        assert!(status == sgx_status_t::SGX_SUCCESS);
+    }
+}

src/libos/src/syscall/mod.rs

@@ -182,6 +182,9 @@ pub extern "C" fn dispatch_syscall(
         ),
         SYS_ARCH_PRCTL => do_arch_prctl(arg0 as u32, arg1 as *mut usize),
         SYS_SET_TID_ADDRESS => do_set_tid_address(arg0 as *mut pid_t),
+
+        // sched
+        SYS_SCHED_YIELD => do_sched_yield(),
         SYS_SCHED_GETAFFINITY => {
             do_sched_getaffinity(arg0 as pid_t, arg1 as size_t, arg2 as *mut c_uchar)
         }
@@ -991,6 +994,11 @@ fn do_set_tid_address(tidptr: *mut pid_t) -> Result<isize> {
     process::do_set_tid_address(tidptr).map(|tid| tid as isize)
 }
 
+fn do_sched_yield() -> Result<isize> {
+    process::do_sched_yield();
+    Ok(0)
+}
+
 fn do_sched_getaffinity(pid: pid_t, cpusize: size_t, buf: *mut c_uchar) -> Result<isize> {
     // Construct safe Rust types
     let mut buf_slice = {

src/pal/pal.c

@@ -5,6 +5,7 @@
 #include <fcntl.h>
 #include <libgen.h>
 #include <pwd.h>
+#include <sched.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -286,6 +287,11 @@ int ocall_sched_setaffinity(int* error, int pid, size_t cpusize, const unsigned
     return ret;
 }
 
+/* In the Linux implementation, sched_yield() always succeeds */
+void ocall_sched_yield(void) {
+    sched_yield();
+}
+
 void ocall_sync(void) {
     sync();
 }

test/sched/main.c

@@ -154,6 +154,18 @@ static int test_sched_setaffinity_with_null_buffer() {
     return 0;
 }
 
+// ============================================================================
+// Test cases for sched_yield
+// ============================================================================
+
+static int test_sched_yield() {
+    // In the Linux implementation, sched_yield() always succeeds.
+    if (sched_yield() < 0) {
+        THROW_ERROR("check sched yield fail");
+    }
+    return 0;
+}
+
 // ============================================================================
 // Test suite main
 // ============================================================================
@@ -168,6 +180,7 @@ static test_case_t test_cases[] = {
     TEST_CASE(test_sched_setaffinity_with_zero_cpusetsize),
     TEST_CASE(test_sched_getaffinity_with_null_buffer),
     TEST_CASE(test_sched_setaffinity_with_null_buffer),
+    TEST_CASE(test_sched_yield),
 };
 
 int main() {