compiler: use CanonAbi for entry_abi

makes entry_abi a lowering of the ABI string, so now it can be
```json
  "entry_abi": "C",
  "entry_abi": "win64",
  "entry_abi": "aapcs",
```

compiler/rustc_abi/src/canon_abi.rs

@@ -3,7 +3,7 @@ use std::fmt;
 #[cfg(feature = "nightly")]
 use rustc_macros::HashStable_Generic;
 
-use crate::{AbiFromStrErr, ExternAbi};
+use crate::ExternAbi;
 
 /// Calling convention to determine codegen
 ///

compiler/rustc_target/src/spec/json.rs

@@ -2,10 +2,12 @@ use std::borrow::Cow;
 use std::collections::BTreeMap;
 use std::str::FromStr;
 
+use rustc_abi::ExternAbi;
 use serde_json::Value;
 
 use super::{Target, TargetKind, TargetOptions, TargetWarnings};
 use crate::json::{Json, ToJson};
+use crate::spec::AbiMap;
 
 impl Target {
     /// Loads a target descriptor from a JSON object.
@@ -515,18 +517,6 @@ impl Target {
                     }
                 }
             } );
-            ($key_name:ident, Conv) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match super::Conv::from_str(s) {
-                        Ok(c) => {
-                            base.$key_name = c;
-                            Some(Ok(()))
-                        }
-                        Err(e) => Some(Err(e))
-                    }
-                })).unwrap_or(Ok(()))
-            } );
         }
 
         if let Some(j) = obj.remove("target-endian") {
@@ -546,6 +536,7 @@ impl Target {
                 incorrect_type.push("frame-pointer".into())
             }
         }
+
         key!(c_int_width = "target-c-int-width");
         key!(c_enum_min_bits, Option<u64>); // if None, matches c_int_width
         key!(os);
@@ -659,9 +650,23 @@ impl Target {
         key!(supports_stack_protector, bool);
         key!(small_data_threshold_support, SmallDataThresholdSupport)?;
         key!(entry_name);
-        key!(entry_abi, Conv)?;
         key!(supports_xray, bool);
 
+        // we're going to run `update_from_cli`, but that won't change the target's AbiMap
+        // FIXME: better factor the Target definition so we enforce this on a type level
+        let abi_map = AbiMap::from_target(&base);
+
+        if let Some(abi_str) = obj.remove("entry-abi") {
+            if let Json::String(abi_str) = abi_str {
+                match abi_str.parse::<ExternAbi>() {
+                    Ok(abi) => base.options.entry_abi = abi_map.canonize_abi(abi, false).unwrap(),
+                    Err(_) => return Err(format!("{abi_str} is not a valid ExternAbi")),
+                }
+            } else {
+                incorrect_type.push("entry-abi".to_owned())
+            }
+        }
+
         base.update_from_cli();
         base.check_consistency(TargetKind::Json)?;
 

compiler/rustc_target/src/spec/mod.rs

@@ -43,7 +43,7 @@ use std::str::FromStr;
 use std::{fmt, io};
 
 use rustc_abi::{
-    Align, Endian, ExternAbi, Integer, Size, TargetDataLayout, TargetDataLayoutErrors,
+    Align, CanonAbi, Endian, ExternAbi, Integer, Size, TargetDataLayout, TargetDataLayoutErrors,
 };
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_fs_util::try_canonicalize;
@@ -53,7 +53,6 @@ use rustc_span::{Symbol, kw, sym};
 use serde_json::Value;
 use tracing::debug;
 
-use crate::callconv::Conv;
 use crate::json::{Json, ToJson};
 use crate::spec::crt_objects::CrtObjects;
 
@@ -2657,9 +2656,9 @@ pub struct TargetOptions {
     /// Default value is "main"
     pub entry_name: StaticCow<str>,
 
-    /// The ABI of entry function.
-    /// Default value is `Conv::C`, i.e. C call convention
-    pub entry_abi: Conv,
+    /// The ABI of the entry function.
+    /// Default value is `CanonAbi::C`
+    pub entry_abi: CanonAbi,
 
     /// Whether the target supports XRay instrumentation.
     pub supports_xray: bool,
@@ -2890,7 +2889,7 @@ impl Default for TargetOptions {
             generate_arange_section: true,
             supports_stack_protector: true,
             entry_name: "main".into(),
-            entry_abi: Conv::C,
+            entry_abi: CanonAbi::C,
             supports_xray: false,
             small_data_threshold_support: SmallDataThresholdSupport::DefaultForArch,
         }

compiler/rustc_target/src/spec/targets/x86_64_unknown_uefi.rs

@@ -5,7 +5,8 @@
 // The win64 ABI is used. It differs from the sysv64 ABI, so we must use a windows target with
 // LLVM. "x86_64-unknown-windows" is used to get the minimal subset of windows-specific features.
 
-use crate::callconv::Conv;
+use rustc_abi::{CanonAbi, X86Call};
+
 use crate::spec::{RustcAbi, Target, TargetMetadata, base};
 
 pub(crate) fn target() -> Target {
@@ -13,7 +14,7 @@ pub(crate) fn target() -> Target {
     base.cpu = "x86-64".into();
     base.plt_by_default = false;
     base.max_atomic_width = Some(64);
-    base.entry_abi = Conv::X86_64Win64;
+    base.entry_abi = CanonAbi::X86(X86Call::Win64);
 
     // We disable MMX and SSE for now, even though UEFI allows using them. Problem is, you have to
     // enable these CPU features explicitly before their first use, otherwise their instructions