diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index 3864db9ffc1bc..d05d09a11eacd 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -1036,7 +1036,8 @@ unsafe fn embed_bitcode(
     // reason (see issue #90326 for historical background).
     let is_apple = cgcx.opts.target_triple.triple().contains("-ios")
         || cgcx.opts.target_triple.triple().contains("-darwin")
-        || cgcx.opts.target_triple.triple().contains("-tvos");
+        || cgcx.opts.target_triple.triple().contains("-tvos")
+        || cgcx.opts.target_triple.triple().contains("-watchos");
     if is_apple
         || cgcx.opts.target_triple.triple().starts_with("wasm")
         || cgcx.opts.target_triple.triple().starts_with("asmjs")
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 82213e7d74847..e70509f3ecc4b 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -2606,7 +2606,7 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
     let os = &sess.target.os;
     let llvm_target = &sess.target.llvm_target;
     if sess.target.vendor != "apple"
-        || !matches!(os.as_ref(), "ios" | "tvos")
+        || !matches!(os.as_ref(), "ios" | "tvos" | "watchos")
         || flavor != LinkerFlavor::Gcc
     {
         return;
@@ -2616,11 +2616,16 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
         ("x86_64", "tvos") => "appletvsimulator",
         ("arm", "ios") => "iphoneos",
         ("aarch64", "ios") if llvm_target.contains("macabi") => "macosx",
-        ("aarch64", "ios") if llvm_target.contains("sim") => "iphonesimulator",
+        ("aarch64", "ios") if llvm_target.ends_with("-simulator") => "iphonesimulator",
         ("aarch64", "ios") => "iphoneos",
         ("x86", "ios") => "iphonesimulator",
         ("x86_64", "ios") if llvm_target.contains("macabi") => "macosx",
         ("x86_64", "ios") => "iphonesimulator",
+        ("x86_64", "watchos") => "watchsimulator",
+        ("arm64_32", "watchos") => "watchos",
+        ("aarch64", "watchos") if llvm_target.ends_with("-simulator") => "watchsimulator",
+        ("aarch64", "watchos") => "watchos",
+        ("arm", "watchos") => "watchos",
         _ => {
             sess.err(&format!("unsupported arch `{}` for os `{}`", arch, os));
             return;
@@ -2667,6 +2672,11 @@ fn get_apple_sdk_root(sdk_name: &str) -> Result<String, String> {
             "macosx10.15"
                 if sdkroot.contains("iPhoneOS.platform")
                     || sdkroot.contains("iPhoneSimulator.platform") => {}
+            "watchos"
+                if sdkroot.contains("WatchSimulator.platform")
+                    || sdkroot.contains("MacOSX.platform") => {}
+            "watchsimulator"
+                if sdkroot.contains("WatchOS.platform") || sdkroot.contains("MacOSX.platform") => {}
             // Ignore `SDKROOT` if it's not a valid path.
             _ if !p.is_absolute() || p == Path::new("/") || !p.exists() => {}
             _ => return Ok(sdkroot),
diff --git a/compiler/rustc_target/src/spec/aarch64_apple_watchos_sim.rs b/compiler/rustc_target/src/spec/aarch64_apple_watchos_sim.rs
new file mode 100644
index 0000000000000..3059f42140be4
--- /dev/null
+++ b/compiler/rustc_target/src/spec/aarch64_apple_watchos_sim.rs
@@ -0,0 +1,38 @@
+use super::apple_sdk_base::{opts, Arch};
+use crate::spec::{FramePointer, Target, TargetOptions};
+
+pub fn target() -> Target {
+    let base = opts("watchos", Arch::Arm64_sim);
+
+    // Clang automatically chooses a more specific target based on
+    // WATCHOS_DEPLOYMENT_TARGET.
+    // This is required for the simulator target to pick the right
+    // MACH-O commands, so we do too.
+    let arch = "arm64";
+    let llvm_target = super::apple_base::watchos_sim_llvm_target(arch);
+
+    Target {
+        llvm_target: llvm_target.into(),
+        pointer_width: 64,
+        data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".into(),
+        arch: "aarch64".into(),
+        options: TargetOptions {
+            features: "+neon,+fp-armv8,+apple-a7".into(),
+            max_atomic_width: Some(128),
+            forces_embed_bitcode: true,
+            frame_pointer: FramePointer::NonLeaf,
+            // Taken from a clang build on Xcode 11.4.1.
+            // These arguments are not actually invoked - they just have
+            // to look right to pass App Store validation.
+            bitcode_llvm_cmdline: "-triple\0\
+                arm64-apple-watchos5.0-simulator\0\
+                -emit-obj\0\
+                -disable-llvm-passes\0\
+                -target-abi\0\
+                darwinpcs\0\
+                -Os\0"
+                .into(),
+            ..base
+        },
+    }
+}
diff --git a/compiler/rustc_target/src/spec/apple_base.rs b/compiler/rustc_target/src/spec/apple_base.rs
index 238d3f8bda5ff..e8460a509e2ba 100644
--- a/compiler/rustc_target/src/spec/apple_base.rs
+++ b/compiler/rustc_target/src/spec/apple_base.rs
@@ -114,3 +114,12 @@ pub fn ios_sim_llvm_target(arch: &str) -> String {
     let (major, minor) = ios_deployment_target();
     format!("{}-apple-ios{}.{}.0-simulator", arch, major, minor)
 }
+
+fn watchos_deployment_target() -> (u32, u32) {
+    deployment_target("WATCHOS_DEPLOYMENT_TARGET").unwrap_or((5, 0))
+}
+
+pub fn watchos_sim_llvm_target(arch: &str) -> String {
+    let (major, minor) = watchos_deployment_target();
+    format!("{}-apple-watchos{}.{}.0-simulator", arch, major, minor)
+}
diff --git a/compiler/rustc_target/src/spec/apple_sdk_base.rs b/compiler/rustc_target/src/spec/apple_sdk_base.rs
index e2d08955c089c..ecb6cbd9f8a49 100644
--- a/compiler/rustc_target/src/spec/apple_sdk_base.rs
+++ b/compiler/rustc_target/src/spec/apple_sdk_base.rs
@@ -6,8 +6,10 @@ use Arch::*;
 #[derive(Copy, Clone)]
 pub enum Arch {
     Armv7,
+    Armv7k,
     Armv7s,
     Arm64,
+    Arm64_32,
     I386,
     X86_64,
     X86_64_macabi,
@@ -17,7 +19,7 @@ pub enum Arch {
 
 fn target_abi(arch: Arch) -> &'static str {
     match arch {
-        Armv7 | Armv7s | Arm64 | I386 | X86_64 => "",
+        Armv7 | Armv7k | Armv7s | Arm64 | Arm64_32 | I386 | X86_64 => "",
         X86_64_macabi | Arm64_macabi => "macabi",
         Arm64_sim => "sim",
     }
@@ -26,8 +28,10 @@ fn target_abi(arch: Arch) -> &'static str {
 fn target_cpu(arch: Arch) -> &'static str {
     match arch {
         Armv7 => "cortex-a8", // iOS7 is supported on iPhone 4 and higher
+        Armv7k => "cortex-a8",
         Armv7s => "cortex-a9",
         Arm64 => "apple-a7",
+        Arm64_32 => "apple-s4",
         I386 => "yonah",
         X86_64 => "core2",
         X86_64_macabi => "core2",
@@ -38,7 +42,7 @@ fn target_cpu(arch: Arch) -> &'static str {
 
 fn link_env_remove(arch: Arch) -> Cow<'static, [Cow<'static, str>]> {
     match arch {
-        Armv7 | Armv7s | Arm64 | I386 | X86_64 | Arm64_sim => {
+        Armv7 | Armv7k | Armv7s | Arm64 | Arm64_32 | I386 | X86_64 | Arm64_sim => {
             cvs!["MACOSX_DEPLOYMENT_TARGET"]
         }
         X86_64_macabi | Arm64_macabi => cvs!["IPHONEOS_DEPLOYMENT_TARGET"],
diff --git a/compiler/rustc_target/src/spec/arm64_32_apple_watchos.rs b/compiler/rustc_target/src/spec/arm64_32_apple_watchos.rs
new file mode 100644
index 0000000000000..7b23fe1c482e1
--- /dev/null
+++ b/compiler/rustc_target/src/spec/arm64_32_apple_watchos.rs
@@ -0,0 +1,28 @@
+use super::apple_sdk_base::{opts, Arch};
+use crate::spec::{Target, TargetOptions};
+
+pub fn target() -> Target {
+    let base = opts("watchos", Arch::Arm64_32);
+    Target {
+        llvm_target: "arm64_32-apple-watchos".into(),
+        pointer_width: 32,
+        data_layout: "e-m:o-p:32:32-i64:64-i128:128-n32:64-S128".into(),
+        arch: "aarch64".into(),
+        options: TargetOptions {
+            features: "+neon,+fp-armv8,+apple-a7".into(),
+            max_atomic_width: Some(64),
+            forces_embed_bitcode: true,
+            // These arguments are not actually invoked - they just have
+            // to look right to pass App Store validation.
+            bitcode_llvm_cmdline: "-triple\0\
+                arm64_32-apple-watchos5.0.0\0\
+                -emit-obj\0\
+                -disable-llvm-passes\0\
+                -target-abi\0\
+                darwinpcs\0\
+                -Os\0"
+                .into(),
+            ..base
+        },
+    }
+}
diff --git a/compiler/rustc_target/src/spec/armv7k_apple_watchos.rs b/compiler/rustc_target/src/spec/armv7k_apple_watchos.rs
new file mode 100644
index 0000000000000..af5d1c2ff4581
--- /dev/null
+++ b/compiler/rustc_target/src/spec/armv7k_apple_watchos.rs
@@ -0,0 +1,28 @@
+use super::apple_sdk_base::{opts, Arch};
+use crate::spec::{Target, TargetOptions};
+
+pub fn target() -> Target {
+    let base = opts("watchos", Arch::Armv7k);
+    Target {
+        llvm_target: "armv7k-apple-watchos".into(),
+        pointer_width: 32,
+        data_layout: "e-m:o-p:32:32-Fi8-i64:64-a:0:32-n32-S128".into(),
+        arch: "arm".into(),
+        options: TargetOptions {
+            features: "+v7,+vfp4,+neon".into(),
+            max_atomic_width: Some(64),
+            forces_embed_bitcode: true,
+            // These arguments are not actually invoked - they just have
+            // to look right to pass App Store validation.
+            bitcode_llvm_cmdline: "-triple\0\
+                armv7k-apple-watchos3.0.0\0\
+                -emit-obj\0\
+                -disable-llvm-passes\0\
+                -target-abi\0\
+                darwinpcs\0\
+                -Os\0"
+                .into(),
+            ..base
+        },
+    }
+}
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 4ede0677ab3a6..422af66787579 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -928,6 +928,11 @@ supported_targets! {
     ("aarch64-apple-tvos", aarch64_apple_tvos),
     ("x86_64-apple-tvos", x86_64_apple_tvos),
 
+    ("armv7k-apple-watchos", armv7k_apple_watchos),
+    ("arm64_32-apple-watchos", arm64_32_apple_watchos),
+    ("x86_64-apple-watchos-sim", x86_64_apple_watchos_sim),
+    ("aarch64-apple-watchos-sim", aarch64_apple_watchos_sim),
+
     ("armebv7r-none-eabi", armebv7r_none_eabi),
     ("armebv7r-none-eabihf", armebv7r_none_eabihf),
     ("armv7r-none-eabi", armv7r_none_eabi),
diff --git a/compiler/rustc_target/src/spec/x86_64_apple_watchos_sim.rs b/compiler/rustc_target/src/spec/x86_64_apple_watchos_sim.rs
new file mode 100644
index 0000000000000..4dff3c2f209cd
--- /dev/null
+++ b/compiler/rustc_target/src/spec/x86_64_apple_watchos_sim.rs
@@ -0,0 +1,35 @@
+use super::apple_sdk_base::{opts, Arch};
+use crate::spec::{StackProbeType, Target, TargetOptions};
+
+pub fn target() -> Target {
+    let base = opts("watchos", Arch::X86_64);
+
+    let arch = "x86_64";
+    let llvm_target = super::apple_base::watchos_sim_llvm_target(arch);
+
+    Target {
+        llvm_target: llvm_target.into(),
+        pointer_width: 64,
+        data_layout: "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+            .into(),
+        arch: "x86_64".into(),
+        options: TargetOptions {
+            max_atomic_width: Some(64),
+            // don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
+            stack_probes: StackProbeType::Call,
+            forces_embed_bitcode: true,
+            // Taken from a clang build on Xcode 11.4.1.
+            // These arguments are not actually invoked - they just have
+            // to look right to pass App Store validation.
+            bitcode_llvm_cmdline: "-triple\0\
+                x86_64-apple-watchos5.0-simulator\0\
+                -emit-obj\0\
+                -disable-llvm-passes\0\
+                -target-abi\0\
+                darwinpcs\0\
+                -Os\0"
+                .into(),
+            ..base
+        },
+    }
+}
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 2b0b7f65b07ed..e23498873f3d3 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -315,8 +315,11 @@ impl Step for Llvm {
             cfg.define("LLVM_ENABLE_ZLIB", "OFF");
         }
 
-        // Are we compiling for iOS/tvOS?
-        if target.contains("apple-ios") || target.contains("apple-tvos") {
+        // Are we compiling for iOS/tvOS/watchOS?
+        if target.contains("apple-ios")
+            || target.contains("apple-tvos")
+            || target.contains("apple-watchos")
+        {
             // These two defines prevent CMake from automatically trying to add a MacOSX sysroot, which leads to a compiler error.
             cfg.define("CMAKE_OSX_SYSROOT", "/");
             cfg.define("CMAKE_OSX_DEPLOYMENT_TARGET", "");
diff --git a/src/doc/rustc/src/SUMMARY.md b/src/doc/rustc/src/SUMMARY.md
index 8e2d44c181215..e464564c12078 100644
--- a/src/doc/rustc/src/SUMMARY.md
+++ b/src/doc/rustc/src/SUMMARY.md
@@ -16,6 +16,7 @@
     - [Target Tier Policy](target-tier-policy.md)
     - [Template for Target-specific Documentation](platform-support/TEMPLATE.md)
     - [aarch64-apple-ios-sim](platform-support/aarch64-apple-ios-sim.md)
+    - [\*-apple-watchos\*](platform-support/apple-watchos.md)
     - [armv7-unknown-linux-uclibceabi](platform-support/armv7-unknown-linux-uclibceabi.md)
     - [armv7-unknown-linux-uclibceabihf](platform-support/armv7-unknown-linux-uclibceabihf.md)
     - [\*-kmc-solid_\*](platform-support/kmc-solid.md)
diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
index 4ac09711b0a09..ec93bdd3fd37f 100644
--- a/src/doc/rustc/src/platform-support.md
+++ b/src/doc/rustc/src/platform-support.md
@@ -207,6 +207,7 @@ target | std | host | notes
 -------|:---:|:----:|-------
 `aarch64-apple-ios-macabi` | ? |  | Apple Catalyst on ARM64
 `aarch64-apple-tvos` | * |  | ARM64 tvOS
+[`aarch64-apple-watchos-sim`](platform-support/apple-watchos.md) | ✓ |  | ARM64 Apple WatchOS Simulator
 [`aarch64-kmc-solid_asp3`](platform-support/kmc-solid.md) | ✓ |  | ARM64 SOLID with TOPPERS/ASP3
 [`aarch64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
@@ -220,6 +221,7 @@ target | std | host | notes
 `aarch64-wrs-vxworks` | ? |  |
 `aarch64_be-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (big-endian, ILP32 ABI)
 `aarch64_be-unknown-linux-gnu` | ✓ | ✓ | ARM64 Linux (big-endian)
+[`arm64_32-apple-watchos`](platform-support/apple-watchos.md) | ✓ | | ARM Apple WatchOS 64-bit with 32-bit pointers
 `armv4t-unknown-linux-gnueabi` | ? |  |
 `armv5te-unknown-linux-uclibceabi` | ? |  | ARMv5TE Linux with uClibc
 `armv6-unknown-freebsd` | ✓ | ✓ | ARMv6 FreeBSD
@@ -234,6 +236,7 @@ target | std | host | notes
 [`armv7a-kmc-solid_asp3-eabi`](platform-support/kmc-solid.md) | ✓ |  | ARM SOLID with TOPPERS/ASP3
 [`armv7a-kmc-solid_asp3-eabihf`](platform-support/kmc-solid.md) | ✓ |  | ARM SOLID with TOPPERS/ASP3, hardfloat
 `armv7a-none-eabihf` | * | | ARM Cortex-A, hardfloat
+[`armv7k-apple-watchos`](platform-support/apple-watchos.md) | ✓ | | ARM Apple WatchOS
 `armv7s-apple-ios` | ✓ |  |
 `avr-unknown-gnu-atmega328` | * |  | AVR. Requires `-Z build-std=core`
 `bpfeb-unknown-none` | * |  | BPF (big endian)
@@ -290,6 +293,7 @@ target | std | host | notes
 [`wasm64-unknown-unknown`](platform-support/wasm64-unknown-unknown.md) | ? |  | WebAssembly
 `x86_64-apple-ios-macabi` | ✓ |  | Apple Catalyst on x86_64
 `x86_64-apple-tvos` | * | | x86 64-bit tvOS
+[`x86_64-apple-watchos-sim`](platform-support/apple-watchos.md) | ✓ | | x86 64-bit Apple WatchOS simulator
 [`x86_64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
 `x86_64-pc-windows-msvc` | * |  | 64-bit Windows XP support
 `x86_64-sun-solaris` | ? |  | Deprecated target for 64-bit Solaris 10/11, illumos
diff --git a/src/doc/rustc/src/platform-support/apple-watchos.md b/src/doc/rustc/src/platform-support/apple-watchos.md
new file mode 100644
index 0000000000000..fe4c7c0c88f6d
--- /dev/null
+++ b/src/doc/rustc/src/platform-support/apple-watchos.md
@@ -0,0 +1,55 @@
+# *-apple-watchos
+- arm64_32-apple-watchos
+- armv7k-apple-watchos
+- aarch64-apple-watchos-sim
+- x86_64-apple-watchos-sim
+
+**Tier: 3**
+
+Apple WatchOS targets:
+- Apple WatchOS on Arm 64_32
+- Apple WatchOS on Arm v7k
+- Apple WatchOS Simulator on arm64
+- Apple WatchOS Simulator on x86_64
+
+## Target maintainers
+
+* [@deg4uss3r](https://github.com/deg4uss3r)
+* [@vladimir-ea](https://github.com/vladimir-ea)
+
+## Requirements
+
+These targets are cross-compiled.
+To build these targets Xcode 12 or higher on macOS is required.
+
+## Building the target
+
+The targets can be built by enabling them for a `rustc` build, for example:
+
+```toml
+[build]
+build-stage = 1
+target = ["aarch64-apple-watchos-sim"]
+```
+
+## Building Rust programs
+
+*Note: Building for this target requires the corresponding WatchOS SDK, as provided by Xcode 12+.*
+
+Rust programs can be built for these targets, if `rustc` has been built with support for them, for example:
+
+```text
+rustc --target aarch64-apple-watchos-sim your-code.rs
+```
+
+## Testing
+
+There is no support for running the Rust testsuite on WatchOS or the simulators.
+
+There is no easy way to run simple programs on WatchOS or the WatchOS simulators. Static library builds can be embedded into WatchOS applications.
+
+## Cross-compilation toolchains and C code
+
+This target can be cross-compiled from x86_64 or aarch64 macOS hosts.
+
+Other hosts are not supported for cross-compilation, but might work when also providing the required Xcode SDK.
diff --git a/src/test/ui/check-cfg/well-known-values.stderr b/src/test/ui/check-cfg/well-known-values.stderr
index a1f7e17d778c5..24ce2280c8adf 100644
--- a/src/test/ui/check-cfg/well-known-values.stderr
+++ b/src/test/ui/check-cfg/well-known-values.stderr
@@ -7,7 +7,7 @@ LL | #[cfg(target_os = "linuz")]
    |                   help: did you mean: `"linux"`
    |
    = note: `#[warn(unexpected_cfgs)]` on by default
-   = note: expected values for `target_os` are: android, cuda, dragonfly, emscripten, espidf, freebsd, fuchsia, haiku, hermit, horizon, illumos, ios, l4re, linux, macos, netbsd, none, openbsd, psp, redox, solaris, solid_asp3, tvos, uefi, unknown, vxworks, wasi, windows, xous
+   = note: expected values for `target_os` are: android, cuda, dragonfly, emscripten, espidf, freebsd, fuchsia, haiku, hermit, horizon, illumos, ios, l4re, linux, macos, netbsd, none, openbsd, psp, redox, solaris, solid_asp3, tvos, uefi, unknown, vxworks, wasi, watchos, windows, xous
 
 warning: unexpected `cfg` condition value
   --> $DIR/well-known-values.rs:14:7
diff --git a/src/tools/compiletest/src/raise_fd_limit.rs b/src/tools/compiletest/src/raise_fd_limit.rs
index faded7c802483..bc2946e2c1354 100644
--- a/src/tools/compiletest/src/raise_fd_limit.rs
+++ b/src/tools/compiletest/src/raise_fd_limit.rs
@@ -4,7 +4,7 @@
 /// on the number of cores available.
 ///
 /// This fixes issue #7772.
-#[cfg(any(target_os = "macos", target_os = "ios"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
 #[allow(non_camel_case_types)]
 pub unsafe fn raise_fd_limit() {
     use std::cmp;
diff --git a/src/tools/compiletest/src/util.rs b/src/tools/compiletest/src/util.rs
index bed509d77be77..215af347f17d2 100644
--- a/src/tools/compiletest/src/util.rs
+++ b/src/tools/compiletest/src/util.rs
@@ -31,6 +31,7 @@ const OS_TABLE: &[(&str, &str)] = &[
     ("redox", "redox"),
     ("sgx", "sgx"),
     ("solaris", "solaris"),
+    ("watchos", "watchos"),
     ("win32", "windows"),
     ("windows", "windows"),
     ("vxworks", "vxworks"),