Rollup merge of rust-lang#136037 - no1wudi:doc, r=jieyouxu

Mark all NuttX targets as tier 3 target and support the standard library

The support for standard library added by rust-lang#130595.

Author: GuillaumeGomez

compiler/rustc_target/src/spec/targets/aarch64_unknown_nuttx.rs

@@ -36,7 +36,7 @@ pub(crate) fn target() -> Target {
             description: Some("AArch64 NuttX".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32".into(),

compiler/rustc_target/src/spec/targets/armv7a_nuttx_eabi.rs

@@ -31,7 +31,7 @@ pub(crate) fn target() -> Target {
             description: Some("ARMv7-A Cortex-A with NuttX".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),

compiler/rustc_target/src/spec/targets/armv7a_nuttx_eabihf.rs

@@ -31,7 +31,7 @@ pub(crate) fn target() -> Target {
             description: Some("ARMv7-A Cortex-A with NuttX (hard float)".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),

compiler/rustc_target/src/spec/targets/riscv32imac_unknown_nuttx_elf.rs

@@ -6,9 +6,9 @@ pub(crate) fn target() -> Target {
         llvm_target: "riscv32".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         pointer_width: 32,
         arch: "riscv32".into(),

compiler/rustc_target/src/spec/targets/riscv32imafc_unknown_nuttx_elf.rs

@@ -6,9 +6,9 @@ pub(crate) fn target() -> Target {
         llvm_target: "riscv32".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         pointer_width: 32,
         arch: "riscv32".into(),

compiler/rustc_target/src/spec/targets/riscv32imc_unknown_nuttx_elf.rs

@@ -6,9 +6,9 @@ pub(crate) fn target() -> Target {
         llvm_target: "riscv32".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         pointer_width: 32,
         arch: "riscv32".into(),

compiler/rustc_target/src/spec/targets/riscv64gc_unknown_nuttx_elf.rs

@@ -8,9 +8,9 @@ pub(crate) fn target() -> Target {
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         llvm_target: "riscv64".into(),
         pointer_width: 64,

compiler/rustc_target/src/spec/targets/riscv64imac_unknown_nuttx_elf.rs

@@ -8,9 +8,9 @@ pub(crate) fn target() -> Target {
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         llvm_target: "riscv64".into(),
         pointer_width: 64,

compiler/rustc_target/src/spec/targets/thumbv6m_nuttx_eabi.rs

@@ -7,9 +7,9 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv6m-none-eabi".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),
@@ -22,12 +22,9 @@ pub(crate) fn target() -> Target {
             llvm_floatabi: Some(FloatAbi::Soft),
             // The ARMv6-M architecture doesn't support unaligned loads/stores so we disable them
             // with +strict-align.
-            // Also force-enable 32-bit atomics, which allows the use of atomic load/store only.
-            // The resulting atomics are ABI incompatible with atomics backed by libatomic.
-            features: "+strict-align,+atomics-32".into(),
-            // There are no atomic CAS instructions available in the instruction set of the ARMv6-M
-            // architecture
-            atomic_cas: false,
+            // The ARMv6-M doesn't support hardware atomic operations, use atomic builtins instead.
+            features: "+strict-align".into(),
+            max_atomic_width: Some(32),
             ..base::thumb::opts()
         },
     }

compiler/rustc_target/src/spec/targets/thumbv7a_nuttx_eabi.rs

@@ -11,9 +11,9 @@ pub(crate) fn target() -> Target {
         llvm_target: "thumbv7a-none-eabi".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
-            tier: None,
+            tier: Some(3),
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),