Create a generic AVR target: avr-none

This commit removes the `avr-unknown-gnu-atmega328` target and replaces
it with a more generic `avr-none` variant that must be specialized with
the `-C target-cpu` flag (e.g. `-C target-cpu=atmega328p`).

2 files changed, 13 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 105a4cb81f0..0399ea77c72 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -1990,6 +1990,7 @@ fn add_pre_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor)
     if let Some(args) = sess.target.pre_link_args.get(&flavor) {
         cmd.verbatim_args(args.iter().map(Deref::deref));
     }
+
     cmd.verbatim_args(&sess.opts.unstable_opts.pre_link_args);
 }
 
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index e3ace01c1eb..8900405c1b8 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -153,6 +153,7 @@ pub(crate) fn get_linker<'a>(
             hinted_static: None,
             is_ld: cc == Cc::No,
             is_gnu: flavor.is_gnu(),
+            uses_lld: flavor.uses_lld(),
         }) as Box<dyn Linker>,
         LinkerFlavor::Msvc(..) => Box::new(MsvcLinker { cmd, sess }) as Box<dyn Linker>,
         LinkerFlavor::EmCc => Box::new(EmLinker { cmd, sess }) as Box<dyn Linker>,
@@ -361,6 +362,7 @@ struct GccLinker<'a> {
     // Link as ld
     is_ld: bool,
     is_gnu: bool,
+    uses_lld: bool,
 }
 
 impl<'a> GccLinker<'a> {
@@ -552,6 +554,7 @@ impl<'a> Linker for GccLinker<'a> {
                 self.link_args(&["--entry", "_initialize"]);
             }
         }
+
         // VxWorks compiler driver introduced `--static-crt` flag specifically for rustc,
         // it switches linking for libc and similar system libraries to static without using
         // any `#[link]` attributes in the `libc` crate, see #72782 for details.
@@ -567,6 +570,15 @@ impl<'a> Linker for GccLinker<'a> {
         {
             self.cc_arg("--static-crt");
         }
+
+        // avr-none doesn't have default ISA, users must specify which specific
+        // CPU (well, microcontroller) they are targetting using `-Ctarget-cpu`.
+        //
+        // Currently this makes sense only when using avr-gcc as a linker, since
+        // it brings a couple of hand-written important intrinsics from libgcc.
+        if self.sess.target.arch == "avr" && !self.uses_lld {
+            self.verbatim_arg(format!("-mmcu={}", self.target_cpu));
+        }
     }
 
     fn link_dylib_by_name(&mut self, name: &str, verbatim: bool, as_needed: bool) {