diff --git a/build.zig b/build.zig
index a97142b090..223c225383 100644
--- a/build.zig
+++ b/build.zig
@@ -96,9 +96,9 @@ fn findLLVM(b: &Builder) -> LibraryDep {
         const args1 = [][]const u8{"llvm-config-5.0", "--libs", "--system-libs"};
         const args2 = [][]const u8{"llvm-config", "--libs", "--system-libs"};
         const max_output_size = 10 * 1024;
-        const good_result = exec(b.allocator, args1, null, null, max_output_size) %% |err| {
+        const good_result = os.ChildProcess.exec(b.allocator, args1, null, null, max_output_size) %% |err| {
             if (err == error.FileNotFound) {
-                exec(b.allocator, args2, null, null, max_output_size) %% |err2| {
+                os.ChildProcess.exec(b.allocator, args2, null, null, max_output_size) %% |err2| {
                     std.debug.panic("unable to spawn {}: {}\n", args2[0], err2);
                 }
             } else {
@@ -121,9 +121,9 @@ fn findLLVM(b: &Builder) -> LibraryDep {
         const args1 = [][]const u8{"llvm-config-5.0", "--includedir"};
         const args2 = [][]const u8{"llvm-config", "--includedir"};
         const max_output_size = 10 * 1024;
-        const good_result = exec(b.allocator, args1, null, null, max_output_size) %% |err| {
+        const good_result = os.ChildProcess.exec(b.allocator, args1, null, null, max_output_size) %% |err| {
             if (err == error.FileNotFound) {
-                exec(b.allocator, args2, null, null, max_output_size) %% |err2| {
+                os.ChildProcess.exec(b.allocator, args2, null, null, max_output_size) %% |err2| {
                     std.debug.panic("unable to spawn {}: {}\n", args2[0], err2);
                 }
             } else {
@@ -146,9 +146,9 @@ fn findLLVM(b: &Builder) -> LibraryDep {
         const args1 = [][]const u8{"llvm-config-5.0", "--libdir"};
         const args2 = [][]const u8{"llvm-config", "--libdir"};
         const max_output_size = 10 * 1024;
-        const good_result = exec(b.allocator, args1, null, null, max_output_size) %% |err| {
+        const good_result = os.ChildProcess.exec(b.allocator, args1, null, null, max_output_size) %% |err| {
             if (err == error.FileNotFound) {
-                exec(b.allocator, args2, null, null, max_output_size) %% |err2| {
+                os.ChildProcess.exec(b.allocator, args2, null, null, max_output_size) %% |err2| {
                     std.debug.panic("unable to spawn {}: {}\n", args2[0], err2);
                 }
             } else {
@@ -203,41 +203,3 @@ fn findLLVM(b: &Builder) -> LibraryDep {
     }
     return result;
 }
-
-
-// TODO move to std lib
-const ExecResult = struct {
-    term: os.ChildProcess.Term,
-    stdout: []u8,
-    stderr: []u8,
-};
-
-fn exec(allocator: &std.mem.Allocator, argv: []const []const u8, cwd: ?[]const u8, env_map: ?&const BufMap, max_output_size: usize) -> %ExecResult {
-    const child = %%os.ChildProcess.init(argv, allocator);
-    defer child.deinit();
-
-    child.stdin_behavior = os.ChildProcess.StdIo.Ignore;
-    child.stdout_behavior = os.ChildProcess.StdIo.Pipe;
-    child.stderr_behavior = os.ChildProcess.StdIo.Pipe;
-    child.cwd = cwd;
-    child.env_map = env_map;
-
-    %return child.spawn();
-
-    var stdout = Buffer.initNull(allocator);
-    var stderr = Buffer.initNull(allocator);
-    defer Buffer.deinit(&stdout);
-    defer Buffer.deinit(&stderr);
-
-    var stdout_file_in_stream = io.FileInStream.init(&??child.stdout);
-    var stderr_file_in_stream = io.FileInStream.init(&??child.stderr);
-
-    %return stdout_file_in_stream.stream.readAllBuffer(&stdout, max_output_size);
-    %return stderr_file_in_stream.stream.readAllBuffer(&stderr, max_output_size);
-
-    return ExecResult {
-        .term = %return child.wait(),
-        .stdout = stdout.toOwnedSlice(),
-        .stderr = stderr.toOwnedSlice(),
-    };
-}
diff --git a/std/os/child_process.zig b/std/os/child_process.zig
index 75a2dcf24d..5aa1578583 100644
--- a/std/os/child_process.zig
+++ b/std/os/child_process.zig
@@ -5,7 +5,6 @@ const os = std.os;
 const posix = os.posix;
 const windows = os.windows;
 const mem = std.mem;
-const Allocator = mem.Allocator;
 const debug = std.debug;
 const assert = debug.assert;
 const BufMap = std.BufMap;
@@ -74,7 +73,7 @@ pub const ChildProcess = struct {
 
     /// First argument in argv is the executable.
     /// On success must call deinit.
-    pub fn init(argv: []const []const u8, allocator: &Allocator) -> %&ChildProcess {
+    pub fn init(argv: []const []const u8, allocator: &mem.Allocator) -> %&ChildProcess {
         const child = %return allocator.create(ChildProcess);
         %defer allocator.destroy(child);
 
@@ -180,6 +179,46 @@ pub const ChildProcess = struct {
         }
     }
 
+    pub const ExecResult = struct {
+        term: os.ChildProcess.Term,
+        stdout: []u8,
+        stderr: []u8,
+    };
+
+    /// Spawns a child process, waits for it, collecting stdout and stderr, and then returns.
+    /// If it succeeds, the caller owns result.stdout and result.stderr memory.
+    pub fn exec(allocator: &mem.Allocator, argv: []const []const u8, cwd: ?[]const u8,
+        env_map: ?&const BufMap, max_output_size: usize) -> %ExecResult
+    {
+        const child = %%ChildProcess.init(argv, allocator);
+        defer child.deinit();
+
+        child.stdin_behavior = ChildProcess.StdIo.Ignore;
+        child.stdout_behavior = ChildProcess.StdIo.Pipe;
+        child.stderr_behavior = ChildProcess.StdIo.Pipe;
+        child.cwd = cwd;
+        child.env_map = env_map;
+
+        %return child.spawn();
+
+        var stdout = Buffer.initNull(allocator);
+        var stderr = Buffer.initNull(allocator);
+        defer Buffer.deinit(&stdout);
+        defer Buffer.deinit(&stderr);
+
+        var stdout_file_in_stream = io.FileInStream.init(&??child.stdout);
+        var stderr_file_in_stream = io.FileInStream.init(&??child.stderr);
+
+        %return stdout_file_in_stream.stream.readAllBuffer(&stdout, max_output_size);
+        %return stderr_file_in_stream.stream.readAllBuffer(&stderr, max_output_size);
+
+        return ExecResult {
+            .term = %return child.wait(),
+            .stdout = stdout.toOwnedSlice(),
+            .stderr = stderr.toOwnedSlice(),
+        };
+    }
+
     fn waitWindows(self: &ChildProcess) -> %Term {
         if (self.term) |term| {
             self.cleanupStreams();
@@ -589,6 +628,7 @@ pub const ChildProcess = struct {
             StdIo.Ignore => %return os.posixDup2(dev_null_fd, std_fileno),
         }
     }
+
 };
 
 fn windowsCreateProcess(app_name: &u8, cmd_line: &u8, envp_ptr: ?&u8, cwd_ptr: ?&u8,
@@ -611,7 +651,7 @@ fn windowsCreateProcess(app_name: &u8, cmd_line: &u8, envp_ptr: ?&u8, cwd_ptr: ?
 
 /// Caller must dealloc.
 /// Guarantees a null byte at result[result.len].
-fn windowsCreateCommandLine(allocator: &Allocator, argv: []const []const u8) -> %[]u8 {
+fn windowsCreateCommandLine(allocator: &mem.Allocator, argv: []const []const u8) -> %[]u8 {
     var buf = %return Buffer.initSize(allocator, 0);
     defer buf.deinit();