Convert exit to syscall instead of VM instruction

api/syscalls.json

@@ -126,6 +126,22 @@
         "const_idx": 17,
         "description": "Grow the heap to a new size given in bytes. This is similar to the `brk()` system call on POSIX systems. Note that the heap may be resized to a size larger than requested. The heap size is guaranteed to be a multiple of 8 bytes. If the requested size is smaller than the current heap size, this is a no-op. Returns the new heap size in bytes."
       },
+      {
+        "name": "exit",
+        "args": [
+          [
+            "i8",
+            "status"
+          ]
+        ],
+        "returns": [
+          "void",
+          ""
+        ],
+        "permission": "default_allowed",
+        "const_idx": 11,
+        "description": "End program execution with the specified exit status."
+      },
       {
         "name": "thread_spawn",
         "args": [

doc/syscalls.md

@@ -68,6 +68,14 @@ u64 vm_grow_heap(u64 num_bytes)
 
 Grow the heap to a new size given in bytes. This is similar to the `brk()` system call on POSIX systems. Note that the heap may be resized to a size larger than requested. The heap size is guaranteed to be a multiple of 8 bytes. If the requested size is smaller than the current heap size, this is a no-op. Returns the new heap size in bytes.
 
+## exit
+
+```
+void exit(i8 status)
+```
+
+End program execution with the specified exit status.
+
 ## thread_spawn
 
 ```

ncc/include/assert.h

@@ -11,7 +11,7 @@
     asm () -> void { syscall print_endl; };\
     asm ("assert(" #test_expr ")") -> void { syscall print_str; };\
     asm () -> void { syscall print_endl; };\
-    asm () -> void { push -1; exit; };\
+    asm () -> void { push -1; syscall exit; };\
 }
 #else
 #define assert(test_val) {}

ncc/include/stdlib.h

@@ -11,9 +11,10 @@ int abs(int n)
     return n;
 }
 
+#undef exit
 void exit(int status)
 {
-    asm (status) -> void { exit; };
+    asm (status) -> void { syscall exit; };
 }
 
 // Convert long int to string

ncc/include/uvm/syscalls.h

@@ -29,6 +29,10 @@
 // Grow the heap to a new size given in bytes. This is similar to the `brk()` system call on POSIX systems. Note that the heap may be resized to a size larger than requested. The heap size is guaranteed to be a multiple of 8 bytes. If the requested size is smaller than the current heap size, this is a no-op. Returns the new heap size in bytes.
 #define vm_grow_heap(__num_bytes) asm (__num_bytes) -> u64 { syscall vm_grow_heap; }
 
+// void exit(i8 status)
+// End program execution with the specified exit status.
+#define exit(__status) asm (__status) -> void { syscall exit; }
+
 // u64 thread_spawn(void* fptr, void* arg)
 // Spawn a new thread running the given function with the argument value `arg`.
 #define thread_spawn(__fptr, __arg) asm (__fptr, __arg) -> u64 { syscall thread_spawn; }

ncc/src/codegen.rs

@@ -165,14 +165,14 @@ impl Unit
 
             out.push_str("# call the main function and then exit\n");
             out.push_str("call main, 0;\n");
-            out.push_str("exit;\n");
+            out.push_str("ret;\n");
             out.push_str("\n");
         }
         else
         {
             // If there is no main function, the unit should just exit (do nothing)
             out.push_str("push 0;\n");
-            out.push_str("exit;\n");
+            out.push_str("ret;\n");
             out.push_str("\n");
         }
 

vm/examples/empty.asm

@@ -1,2 +1,2 @@
 push 0;
-exit;
+ret;

vm/examples/factorial.asm

@@ -22,7 +22,7 @@ syscall print_i64;
 syscall print_endl;
 
 push 0;
-exit;
+ret;
 
 #### fact(n) ####
 FACT:

vm/examples/fib.asm

@@ -22,7 +22,7 @@ syscall print_i64;
 syscall print_endl;
 
 push 0;
-exit;
+ret;
 
 #
 # u64 fib(u64 n)

vm/examples/fizzbuzz.asm

@@ -58,4 +58,4 @@ push 101;
 lt_i64; # l0 < COUNT
 jnz LOOP;
 
-exit;
+ret;

vm/examples/guess.asm

@@ -84,7 +84,7 @@ syscall print_i64;
 syscall print_endl;
 
 push 0;
-exit;
+ret;
 
 #
 # Read a positive integer from stdlin

vm/examples/loop.asm

@@ -61,4 +61,4 @@ push MIPS_STR;
 syscall print_str;
 syscall print_endl;
 
-exit;
+ret;

vm/examples/memcpy.asm

@@ -73,4 +73,4 @@ push FPS_STR;
 syscall print_str;
 syscall print_endl;
 
-exit;
+ret;

vm/src/asm.rs

@@ -1169,7 +1169,6 @@ impl Assembler
             }
 
             "ret" => self.code.push_op(Op::ret),
-            "exit" => self.code.push_op(Op::exit),
 
             _ => {
                 return input.parse_error(&format!("unknown instruction opcode \"{}\"", op_name))
@@ -1323,7 +1322,7 @@ mod tests
         parse_ok(" FOO_BAR:   jmp  FOO_BAR; ");
 
         // Callback label
-        parse_ok("CB: ret; push_p32 CB; exit;");
+        parse_ok("CB: ret; push_p32 CB; ret;");
     }
 
     #[test]

vm/src/constants.rs

@@ -17,6 +17,7 @@ pub const PRINT_ENDL: u16 = 7;
 pub const GETCHAR: u16 = 8;
 pub const WINDOW_POLL_EVENT: u16 = 9;
 pub const WINDOW_DRAW_FRAME: u16 = 10;
+pub const EXIT: u16 = 11;
 pub const VM_HEAP_SIZE: u16 = 14;
 pub const MEMSET32: u16 = 16;
 pub const VM_GROW_HEAP: u16 = 17;
@@ -54,7 +55,7 @@ pub const SYSCALL_DESCS: [Option<SysCallDesc>; SYSCALL_TBL_LEN] = [
     Some(SysCallDesc { name: "getchar", const_idx: 8, argc: 0, has_ret: true }),
     Some(SysCallDesc { name: "window_poll_event", const_idx: 9, argc: 1, has_ret: true }),
     Some(SysCallDesc { name: "window_draw_frame", const_idx: 10, argc: 2, has_ret: false }),
-    None,
+    Some(SysCallDesc { name: "exit", const_idx: 11, argc: 1, has_ret: false }),
     None,
     None,
     Some(SysCallDesc { name: "vm_heap_size", const_idx: 14, argc: 0, has_ret: true }),

vm/src/host.rs

@@ -97,6 +97,7 @@ pub fn get_syscall(const_idx: u16) -> HostFn
         MEMSET32 => HostFn::Fn3_0(memset32),
         MEMCPY => HostFn::Fn3_0(memcpy),
         MEMCMP => HostFn::Fn3_1(memcmp),
+        EXIT => HostFn::Fn1_0(exit),
 
         THREAD_SPAWN => HostFn::Fn2_1(thread_spawn),
         THREAD_JOIN => HostFn::Fn1_1(thread_join),
@@ -224,6 +225,12 @@ fn memcmp(thread: &mut Thread, ptr_a: Value, ptr_b: Value, num_bytes: Value) ->
     }
 }
 
+// End program execution
+fn exit(thread: &mut Thread, val: Value)
+{
+    unsafe { libc::exit(val.as_i32() & 0xFF) };
+}
+
 fn print_i64(thread: &mut Thread, v: Value)
 {
     let v = v.as_i64();