Add built in target, based on msp430. This uses external gcc to generate object files

Author: MabezDev

src/librustc_target/spec/mod.rs

@@ -448,6 +448,7 @@ supported_targets! {
     ("thumbv8m.main-none-eabihf", thumbv8m_main_none_eabihf),
 
     ("msp430-none-elf", msp430_none_elf),
+    ("xtensa-none-elf", xtensa_none_elf),
 
     ("aarch64-unknown-cloudabi", aarch64_unknown_cloudabi),
     ("armv7-unknown-cloudabi-eabihf", armv7_unknown_cloudabi_eabihf),

src/librustc_target/spec/xtensa_none_elf.rs

@@ -0,0 +1,66 @@
+use crate::spec::{LinkerFlavor, PanicStrategy, Target, TargetOptions, TargetResult, abi::Abi}; 
+// use crate::spec::abi::Abi;
+
+pub fn target() -> TargetResult {
+    Ok(Target {
+        llvm_target: "xtensa-none-elf".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-i1:8:32-i8:8:32-i16:16:32-i64:64-f64:64-a:0:32-n32".to_string(),
+        arch: "xtensa".to_string(),
+        target_os: "none".to_string(),
+        target_env: String::new(),
+        target_vendor: String::new(),
+        linker_flavor: LinkerFlavor::Gcc,
+
+        options: TargetOptions {
+            executables: true,
+
+            // The LLVM backend currently can't generate object files. To
+            // workaround this LLVM generates assembly files which then we feed
+            // to gcc to get object files. For this reason we have a hard
+            // dependency on this specific gcc.
+            // asm_args: vec!["-mcpu=generic".to_string()],
+            linker: Some("xtensa-esp32-elf-gcc".to_string()),
+            no_integrated_as: true,
+
+            max_atomic_width: Some(32),
+            atomic_cas: true,
+
+            // Because these devices have very little resources having an
+            // unwinder is too onerous so we default to "abort" because the
+            // "unwind" strategy is very rare.
+            panic_strategy: PanicStrategy::Abort,
+
+            // Similarly, one almost always never wants to use relocatable
+            // code because of the extra costs it involves.
+            relocation_model: "static".to_string(),
+
+            // Right now we invoke an external assembler and this isn't
+            // compatible with multiple codegen units, and plus we probably
+            // don't want to invoke that many gcc instances.
+            default_codegen_units: Some(1),
+
+            // Since MSP430 doesn't meaningfully support faulting on illegal
+            // instructions, LLVM generates a call to abort() function instead
+            // of a trap instruction. Such calls are 4 bytes long, and that is
+            // too much overhead for such small target.
+            trap_unreachable: false,
+
+            // See the thumb_base.rs file for an explanation of this value
+            emit_debug_gdb_scripts: false,
+
+            abi_blacklist: vec![
+                Abi::Stdcall,
+                Abi::Fastcall,
+                Abi::Vectorcall,
+                Abi::Thiscall,
+                Abi::Win64,
+                Abi::SysV64,
+            ],
+
+            .. Default::default( )
+        }
+    })
+}