diff --git a/lib/std/build.zig b/lib/std/build.zig
index 4d2fbabcae..9bac20df4b 100644
--- a/lib/std/build.zig
+++ b/lib/std/build.zig
@@ -1064,6 +1064,9 @@ pub const LibExeObjStep = struct {
     /// Uses system QEMU installation to run cross compiled foreign architecture build artifacts.
     enable_qemu: bool = false,
 
+    /// Uses system Wasmtime installation to run cross compiled wasm/wasi build artifacts.
+    enable_wasmtime: bool = false,
+
     /// After following the steps in https://github.com/ziglang/zig/wiki/Updating-libc#glibc,
     /// this will be the directory $glibc-build-dir/install/glibcs
     /// Given the example of the aarch64 target, this is the directory
@@ -1863,6 +1866,11 @@ pub const LibExeObjStep = struct {
                 try zig_args.append(bin_name);
                 try zig_args.append("--test-cmd-bin");
             },
+            .wasmtime => |bin_name| if (self.enable_wasmtime) {
+                try zig_args.append("--test-cmd");
+                try zig_args.append(bin_name);
+                try zig_args.append("--test-cmd-bin");
+            },
         }
         for (self.packages.toSliceConst()) |pkg| {
             zig_args.append("--pkg-begin") catch unreachable;
diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 9df7370ad0..226574b3dd 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -213,7 +213,8 @@ pub fn assert(ok: bool) void {
 
 pub fn panic(comptime format: []const u8, args: ...) noreturn {
     @setCold(true);
-    const first_trace_addr = @returnAddress();
+    // TODO: remove conditional once wasi / LLVM defines __builtin_return_address
+    const first_trace_addr = if (builtin.os == .wasi) null else @returnAddress();
     panicExtra(null, first_trace_addr, format, args);
 }
 
diff --git a/lib/std/heap.zig b/lib/std/heap.zig
index dae836611e..259c29f6e6 100644
--- a/lib/std/heap.zig
+++ b/lib/std/heap.zig
@@ -33,11 +33,19 @@ fn cShrink(self: *Allocator, old_mem: []u8, old_align: u29, new_size: usize, new
 
 /// This allocator makes a syscall directly for every allocation and free.
 /// Thread-safe and lock-free.
-pub const page_allocator = &page_allocator_state;
+pub const page_allocator = if (std.Target.current.isWasm())
+    &wasm_page_allocator_state
+else
+    &page_allocator_state;
+
 var page_allocator_state = Allocator{
     .reallocFn = PageAllocator.realloc,
     .shrinkFn = PageAllocator.shrink,
 };
+var wasm_page_allocator_state = Allocator{
+    .reallocFn = WasmPageAllocator.realloc,
+    .shrinkFn = WasmPageAllocator.shrink,
+};
 
 /// Deprecated. Use `page_allocator`.
 pub const direct_allocator = page_allocator;
@@ -238,6 +246,88 @@ const PageAllocator = struct {
     }
 };
 
+// TODO Exposed LLVM intrinsics is a bug
+// See: https://github.com/ziglang/zig/issues/2291
+extern fn @"llvm.wasm.memory.size.i32"(u32) u32;
+extern fn @"llvm.wasm.memory.grow.i32"(u32, u32) i32;
+
+/// TODO: make this re-use freed pages, and cooperate with other callers of these global intrinsics
+/// by better utilizing the return value of grow()
+const WasmPageAllocator = struct {
+    var start_ptr: [*]u8 = undefined;
+    var num_pages: usize = 0;
+    var end_index: usize = 0;
+
+    comptime {
+        if (builtin.arch != .wasm32) {
+            @compileError("WasmPageAllocator is only available for wasm32 arch");
+        }
+    }
+
+    fn alloc(allocator: *Allocator, size: usize, alignment: u29) ![]u8 {
+        const addr = @ptrToInt(start_ptr) + end_index;
+        const adjusted_addr = mem.alignForward(addr, alignment);
+        const adjusted_index = end_index + (adjusted_addr - addr);
+        const new_end_index = adjusted_index + size;
+
+        if (new_end_index > num_pages * mem.page_size) {
+            const required_memory = new_end_index - (num_pages * mem.page_size);
+
+            var num_pages: usize = required_memory / mem.page_size;
+            if (required_memory % mem.page_size != 0) {
+                num_pages += 1;
+            }
+
+            const prev_page = @"llvm.wasm.memory.grow.i32"(0, @intCast(u32, num_pages));
+            if (prev_page == -1) {
+                return error.OutOfMemory;
+            }
+
+            num_pages += num_pages;
+        }
+
+        const result = start_ptr[adjusted_index..new_end_index];
+        end_index = new_end_index;
+
+        return result;
+    }
+
+    // Check if memory is the last "item" and is aligned correctly
+    fn is_last_item(memory: []u8, alignment: u29) bool {
+        return memory.ptr == start_ptr + end_index - memory.len and mem.alignForward(@ptrToInt(memory.ptr), alignment) == @ptrToInt(memory.ptr);
+    }
+
+    fn realloc(allocator: *Allocator, old_mem: []u8, old_align: u29, new_size: usize, new_align: u29) ![]u8 {
+        // Initialize start_ptr at the first realloc
+        if (num_pages == 0) {
+            start_ptr = @intToPtr([*]u8, @intCast(usize, @"llvm.wasm.memory.size.i32"(0)) * mem.page_size);
+        }
+
+        if (is_last_item(old_mem, new_align)) {
+            const start_index = end_index - old_mem.len;
+            const new_end_index = start_index + new_size;
+
+            if (new_end_index > num_pages * mem.page_size) {
+                _ = try alloc(allocator, new_end_index - end_index, new_align);
+            }
+            const result = start_ptr[start_index..new_end_index];
+
+            end_index = new_end_index;
+            return result;
+        } else if (new_size <= old_mem.len and new_align <= old_align) {
+            return error.OutOfMemory;
+        } else {
+            const result = try alloc(allocator, new_size, new_align);
+            mem.copy(u8, result, old_mem);
+            return result;
+        }
+    }
+
+    fn shrink(allocator: *Allocator, old_mem: []u8, old_align: u29, new_size: usize, new_align: u29) []u8 {
+        return old_mem[0..new_size];
+    }
+};
+
 pub const HeapAllocator = switch (builtin.os) {
     .windows => struct {
         allocator: Allocator,
@@ -487,103 +577,6 @@ pub const FixedBufferAllocator = struct {
     }
 };
 
-// TODO Exposed LLVM intrinsics is a bug
-// See: https://github.com/ziglang/zig/issues/2291
-extern fn @"llvm.wasm.memory.size.i32"(u32) u32;
-extern fn @"llvm.wasm.memory.grow.i32"(u32, u32) i32;
-
-pub const wasm_allocator = &wasm_allocator_state.allocator;
-var wasm_allocator_state = WasmAllocator{
-    .allocator = Allocator{
-        .reallocFn = WasmAllocator.realloc,
-        .shrinkFn = WasmAllocator.shrink,
-    },
-    .start_ptr = undefined,
-    .num_pages = 0,
-    .end_index = 0,
-};
-
-const WasmAllocator = struct {
-    allocator: Allocator,
-    start_ptr: [*]u8,
-    num_pages: usize,
-    end_index: usize,
-
-    comptime {
-        if (builtin.arch != .wasm32) {
-            @compileError("WasmAllocator is only available for wasm32 arch");
-        }
-    }
-
-    fn alloc(allocator: *Allocator, size: usize, alignment: u29) ![]u8 {
-        const self = @fieldParentPtr(WasmAllocator, "allocator", allocator);
-
-        const addr = @ptrToInt(self.start_ptr) + self.end_index;
-        const adjusted_addr = mem.alignForward(addr, alignment);
-        const adjusted_index = self.end_index + (adjusted_addr - addr);
-        const new_end_index = adjusted_index + size;
-
-        if (new_end_index > self.num_pages * mem.page_size) {
-            const required_memory = new_end_index - (self.num_pages * mem.page_size);
-
-            var num_pages: usize = required_memory / mem.page_size;
-            if (required_memory % mem.page_size != 0) {
-                num_pages += 1;
-            }
-
-            const prev_page = @"llvm.wasm.memory.grow.i32"(0, @intCast(u32, num_pages));
-            if (prev_page == -1) {
-                return error.OutOfMemory;
-            }
-
-            self.num_pages += num_pages;
-        }
-
-        const result = self.start_ptr[adjusted_index..new_end_index];
-        self.end_index = new_end_index;
-
-        return result;
-    }
-
-    // Check if memory is the last "item" and is aligned correctly
-    fn is_last_item(allocator: *Allocator, memory: []u8, alignment: u29) bool {
-        const self = @fieldParentPtr(WasmAllocator, "allocator", allocator);
-        return memory.ptr == self.start_ptr + self.end_index - memory.len and mem.alignForward(@ptrToInt(memory.ptr), alignment) == @ptrToInt(memory.ptr);
-    }
-
-    fn realloc(allocator: *Allocator, old_mem: []u8, old_align: u29, new_size: usize, new_align: u29) ![]u8 {
-        const self = @fieldParentPtr(WasmAllocator, "allocator", allocator);
-
-        // Initialize start_ptr at the first realloc
-        if (self.num_pages == 0) {
-            self.start_ptr = @intToPtr([*]u8, @intCast(usize, @"llvm.wasm.memory.size.i32"(0)) * mem.page_size);
-        }
-
-        if (is_last_item(allocator, old_mem, new_align)) {
-            const start_index = self.end_index - old_mem.len;
-            const new_end_index = start_index + new_size;
-
-            if (new_end_index > self.num_pages * mem.page_size) {
-                _ = try alloc(allocator, new_end_index - self.end_index, new_align);
-            }
-            const result = self.start_ptr[start_index..new_end_index];
-
-            self.end_index = new_end_index;
-            return result;
-        } else if (new_size <= old_mem.len and new_align <= old_align) {
-            return error.OutOfMemory;
-        } else {
-            const result = try alloc(allocator, new_size, new_align);
-            mem.copy(u8, result, old_mem);
-            return result;
-        }
-    }
-
-    fn shrink(allocator: *Allocator, old_mem: []u8, old_align: u29, new_size: usize, new_align: u29) []u8 {
-        return old_mem[0..new_size];
-    }
-};
-
 pub const ThreadSafeFixedBufferAllocator = blk: {
     if (builtin.single_threaded) {
         break :blk FixedBufferAllocator;
diff --git a/lib/std/os.zig b/lib/std/os.zig
index 7fcdb7f3ff..a616fbc49f 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -1527,7 +1527,7 @@ pub fn isatty(handle: fd_t) bool {
         return system.isatty(handle) != 0;
     }
     if (builtin.os == .wasi) {
-        @compileError("TODO implement std.os.isatty for WASI");
+        return system.isatty(handle);
     }
     if (builtin.os == .linux) {
         var wsz: linux.winsize = undefined;
diff --git a/lib/std/os/bits/wasi.zig b/lib/std/os/bits/wasi.zig
index 93d2a82fde..139418ded2 100644
--- a/lib/std/os/bits/wasi.zig
+++ b/lib/std/os/bits/wasi.zig
@@ -138,7 +138,7 @@ pub const FDFLAG_NONBLOCK: fdflags_t = 0x0004;
 pub const FDFLAG_RSYNC: fdflags_t = 0x0008;
 pub const FDFLAG_SYNC: fdflags_t = 0x0010;
 
-const fdstat_t = extern struct {
+pub const fdstat_t = extern struct {
     fs_filetype: filetype_t,
     fs_flags: fdflags_t,
     fs_rights_base: rights_t,
@@ -298,6 +298,7 @@ pub const subscription_t = extern struct {
 };
 
 pub const timestamp_t = u64;
+pub const time_t = i64; // match https://github.com/CraneStation/wasi-libc
 
 pub const userdata_t = u64;
 
@@ -305,3 +306,8 @@ pub const whence_t = u8;
 pub const WHENCE_CUR: whence_t = 0;
 pub const WHENCE_END: whence_t = 1;
 pub const WHENCE_SET: whence_t = 2;
+
+pub const timespec = extern struct {
+    tv_sec: time_t,
+    tv_nsec: isize,
+};
diff --git a/lib/std/os/wasi.zig b/lib/std/os/wasi.zig
index 7661be1f85..1ffc9610f0 100644
--- a/lib/std/os/wasi.zig
+++ b/lib/std/os/wasi.zig
@@ -76,3 +76,54 @@ pub extern "wasi_unstable" fn sched_yield() errno_t;
 pub extern "wasi_unstable" fn sock_recv(sock: fd_t, ri_data: *const iovec_t, ri_data_len: usize, ri_flags: riflags_t, ro_datalen: *usize, ro_flags: *roflags_t) errno_t;
 pub extern "wasi_unstable" fn sock_send(sock: fd_t, si_data: *const ciovec_t, si_data_len: usize, si_flags: siflags_t, so_datalen: *usize) errno_t;
 pub extern "wasi_unstable" fn sock_shutdown(sock: fd_t, how: sdflags_t) errno_t;
+
+/// Get the errno from a syscall return value, or 0 for no error.
+pub fn getErrno(r: usize) usize {
+    const signed_r = @bitCast(isize, r);
+    return if (signed_r > -4096 and signed_r < 0) @intCast(usize, -signed_r) else 0;
+}
+
+pub fn clock_getres(clock_id: i32, res: *timespec) errno_t {
+    var ts: timestamp_t = undefined;
+    const err = clock_res_get(@bitCast(u32, clock_id), &ts);
+    if (err != 0) {
+        return err;
+    }
+    res.* = .{
+        .tv_sec = @intCast(i64, ts / std.time.ns_per_s),
+        .tv_nsec = @intCast(isize, ts % std.time.ns_per_s),
+    };
+    return 0;
+}
+
+pub fn clock_gettime(clock_id: i32, tp: *timespec) errno_t {
+    var ts: timestamp_t = undefined;
+    const err = clock_time_get(@bitCast(u32, clock_id), 1, &ts);
+    if (err != 0) {
+        return err;
+    }
+    tp.* = .{
+        .tv_sec = @intCast(i64, ts / std.time.ns_per_s),
+        .tv_nsec = @intCast(isize, ts % std.time.ns_per_s),
+    };
+    return 0;
+}
+
+pub fn isatty(fd: fd_t) bool {
+    var statbuf: fdstat_t = undefined;
+    const err = fd_fdstat_get(fd, &statbuf);
+    if (err != 0) {
+        // errno = err;
+        return false;
+    }
+
+    // A tty is a character device that we can't seek or tell on.
+    if (statbuf.fs_filetype != FILETYPE_CHARACTER_DEVICE or
+        (statbuf.fs_rights_base & (RIGHT_FD_SEEK | RIGHT_FD_TELL)) != 0)
+    {
+        // errno = ENOTTY;
+        return false;
+    }
+
+    return true;
+}
diff --git a/lib/std/target.zig b/lib/std/target.zig
index 5c0ac3d905..9652d5b6e5 100644
--- a/lib/std/target.zig
+++ b/lib/std/target.zig
@@ -611,6 +611,7 @@ pub const Target = union(enum) {
         native,
         qemu: []const u8,
         wine: []const u8,
+        wasmtime: []const u8,
         unavailable,
     };
 
@@ -649,6 +650,13 @@ pub const Target = union(enum) {
             }
         }
 
+        if (self.isWasm()) {
+            switch (self.getArchPtrBitWidth()) {
+                32 => return Executor{ .wasmtime = "wasmtime" },
+                else => return .unavailable,
+            }
+        }
+
         return .unavailable;
     }
 };