Auto merge of #55041 - evq:thumbv8m, r=alexcrichton

targets: thumbv8m: Add target for baseline ARMv8-M

Tested against a SAM L11 MCU.

src/librustc_target/spec/mod.rs

@@ -399,6 +399,7 @@ fn $module() {
     ("thumbv7m-none-eabi", thumbv7m_none_eabi),
     ("thumbv7em-none-eabi", thumbv7em_none_eabi),
     ("thumbv7em-none-eabihf", thumbv7em_none_eabihf),
+    ("thumbv8m.base-none-eabi", thumbv8m_base_none_eabi),
 
     ("msp430-none-elf", msp430_none_elf),
 

src/librustc_target/spec/thumb_base.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// These 4 `thumbv*` targets cover the ARM Cortex-M family of processors which are widely used in
+// These `thumbv*` targets cover the ARM Cortex-M family of processors which are widely used in
 // microcontrollers. Namely, all these processors:
 //
 // - Cortex-M0
@@ -17,8 +17,9 @@
 // - Cortex-M3
 // - Cortex-M4(F)
 // - Cortex-M7(F)
+// - Cortex-M23
 //
-// We have opted for 4 targets instead of one target per processor (e.g. `cortex-m0`, `cortex-m3`,
+// We have opted for these instead of one target per processor (e.g. `cortex-m0`, `cortex-m3`,
 // etc) because the differences between some processors like the cortex-m0 and cortex-m1 are almost
 // non-existent from the POV of codegen so it doesn't make sense to have separate targets for them.
 // And if differences exist between two processors under the same target, rustc flags can be used to

src/librustc_target/spec/thumbv8m_base_none_eabi.rs

@@ -0,0 +1,36 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Targets the Cortex-M23 processor (Baseline ARMv8-M)
+
+use spec::{LinkerFlavor, LldFlavor, Target, TargetOptions, TargetResult};
+
+pub fn target() -> TargetResult {
+    Ok(Target {
+        llvm_target: "thumbv8m.base-none-eabi".to_string(),
+        target_endian: "little".to_string(),
+        target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
+        data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
+        arch: "arm".to_string(),
+        target_os: "none".to_string(),
+        target_env: String::new(),
+        target_vendor: String::new(),
+        linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
+
+        options: TargetOptions {
+            // ARMv8-M baseline doesn't support unaligned loads/stores so we disable them
+            // with +strict-align.
+            features: "+strict-align".to_string(),
+            max_atomic_width: Some(32),
+            .. super::thumb_base::opts()
+        },
+    })
+}