feat: Add std Xtensa targets support

compiler/rustc_target/src/spec/mod.rs

@@ -1767,8 +1767,11 @@ supported_targets! {
     ("nvptx64-nvidia-cuda", nvptx64_nvidia_cuda),
 
     ("xtensa-esp32-none-elf", xtensa_esp32_none_elf),
+    ("xtensa-esp32-espidf", xtensa_esp32_espidf),
     ("xtensa-esp32s2-none-elf", xtensa_esp32s2_none_elf),
+    ("xtensa-esp32s2-espidf", xtensa_esp32s2_espidf),
     ("xtensa-esp32s3-none-elf", xtensa_esp32s3_none_elf),
+    ("xtensa-esp32s3-espidf", xtensa_esp32s3_espidf),
 
     ("i686-wrs-vxworks", i686_wrs_vxworks),
     ("x86_64-wrs-vxworks", x86_64_wrs_vxworks),

compiler/rustc_target/src/spec/targets/xtensa_esp32_espidf.rs

@@ -0,0 +1,36 @@
+use crate::abi::Endian;
+use crate::spec::{base::xtensa, cvs, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "xtensa-none-elf".into(),
+        pointer_width: 32,
+        data_layout: "e-m:e-p:32:32-v1:8:8-i64:64-i128:128-n32".into(),
+        arch: "xtensa".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: None,
+            tier: None,
+            host_tools: None,
+            std: None,
+        },
+
+        options: TargetOptions {
+            endian: Endian::Little,
+            c_int_width: "32".into(),
+            families: cvs!["unix"],
+            os: "espidf".into(),
+            env: "newlib".into(),
+            vendor: "espressif".into(),
+
+            executables: true,
+            cpu: "esp32".into(),
+            linker: Some("xtensa-esp32-elf-gcc".into()),
+
+            // The esp32 only supports native 32bit atomics.
+            max_atomic_width: Some(32),
+            atomic_cas: true,
+
+            ..xtensa::opts()
+        },
+    }
+}

compiler/rustc_target/src/spec/targets/xtensa_esp32s2_espidf.rs

@@ -0,0 +1,43 @@
+use crate::abi::Endian;
+use crate::spec::{base::xtensa, cvs, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "xtensa-none-elf".into(),
+        pointer_width: 32,
+        data_layout: "e-m:e-p:32:32-v1:8:8-i64:64-i128:128-n32".into(),
+        arch: "xtensa".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: None,
+            tier: None,
+            host_tools: None,
+            std: None,
+        },
+
+        options: TargetOptions {
+            endian: Endian::Little,
+            c_int_width: "32".into(),
+            families: cvs!["unix"],
+            os: "espidf".into(),
+            env: "newlib".into(),
+            vendor: "espressif".into(),
+
+            executables: true,
+            cpu: "esp32-s2".into(),
+            linker: Some("xtensa-esp32s2-elf-gcc".into()),
+
+            // See https://github.com/espressif/rust-esp32-example/issues/3#issuecomment-861054477
+            //
+            // While the ESP32-S2 chip does not natively support atomics, ESP-IDF does support
+            // the __atomic* and __sync* compiler builtins. Setting `max_atomic_width` and `atomic_cas`
+            // and `atomic_cas: true` will cause the compiler to emit libcalls to these builtins. On the
+            // ESP32-S2, these are guaranteed to be lock-free.
+            //
+            // Support for atomics is necessary for the Rust STD library, which is supported by ESP-IDF.
+            max_atomic_width: Some(32),
+            atomic_cas: true,
+
+            ..xtensa::opts()
+        },
+    }
+}

compiler/rustc_target/src/spec/targets/xtensa_esp32s3_espidf.rs

@@ -0,0 +1,36 @@
+use crate::abi::Endian;
+use crate::spec::{base::xtensa, cvs, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "xtensa-none-elf".into(),
+        pointer_width: 32,
+        data_layout: "e-m:e-p:32:32-v1:8:8-i64:64-i128:128-n32".into(),
+        arch: "xtensa".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: None,
+            tier: None,
+            host_tools: None,
+            std: None,
+        },
+
+        options: TargetOptions {
+            endian: Endian::Little,
+            c_int_width: "32".into(),
+            families: cvs!["unix"],
+            os: "espidf".into(),
+            env: "newlib".into(),
+            vendor: "espressif".into(),
+
+            executables: true,
+            cpu: "esp32-s3".into(),
+            linker: Some("xtensa-esp32s3-elf-gcc".into()),
+
+            // The esp32s3 only supports native 32bit atomics.
+            max_atomic_width: Some(32),
+            atomic_cas: true,
+
+            ..xtensa::opts()
+        },
+    }
+}