fork test

src/main.zig

@@ -356,6 +356,25 @@ test "echo" {
     try testHelper(&.{ "echo", "Hello", "There" }, "Hello There\n");
 }
 
+test "nolibc_nopie_fork" {
+    try testHelper(
+        &.{ flicker_path, getTestExePath("nolibc_nopie_fork") },
+        "Child: I'm alive!\nParent: Child died.\n",
+    );
+}
+test "nolibc_pie_fork" {
+    try testHelper(
+        &.{ flicker_path, getTestExePath("nolibc_pie_fork") },
+        "Child: I'm alive!\nParent: Child died.\n",
+    );
+}
+test "libc_pie_fork" {
+    try testHelper(
+        &.{ flicker_path, getTestExePath("libc_pie_fork") },
+        "Child: I'm alive!\nParent: Child died.\n",
+    );
+}
+
 fn testPrintArgs(comptime name: []const u8) !void {
     const exe_path = getTestExePath(name);
     const loader_argv: []const []const u8 = &.{ flicker_path, exe_path, "foo", "bar", "baz hi" };

src/syscalls.zig

@@ -63,10 +63,6 @@ export fn syscall_handler(regs: *UserRegs) callconv(.c) void {
             std.debug.print("back in `syscall_handler`\n", .{});
             return;
         },
-        .fork, .vfork => {
-            // fork/vfork duplicate the stack (or share it until exec), so the return path via
-            // syscall_entry works fine.
-        },
         .rt_sigreturn => {
             @panic("sigreturn is not supported yet");
         },

src/test/fork.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+const linux = std.os.linux;
+
+pub fn main() !void {
+    const ret = linux.syscall0(.fork);
+    const pid: i32 = @intCast(ret);
+
+    if (pid == 0) {
+        // --- Child ---
+        const msg = "Child: I'm alive!\n";
+        _ = linux.syscall3(.write, 1, @intFromPtr(msg.ptr), msg.len);
+        linux.exit(0);
+    } else if (pid > 0) {
+        // --- Parent ---
+        var status: u32 = 0;
+        _ = linux.syscall4(.wait4, @intCast(pid), @intFromPtr(&status), 0, 0);
+        const msg = "Parent: Child died.\n";
+        _ = linux.syscall3(.write, 1, @intFromPtr(msg.ptr), msg.len);
+    } else {
+        const msg = "Fork failed!\n";
+        _ = linux.syscall3(.write, 1, @intFromPtr(msg.ptr), msg.len);
+    }
+}