4 files changed, 56 insertions, 2 deletions

diff --git a/cortex-m-rt/Cargo.toml b/cortex-m-rt/Cargo.toml
index 3305d34..03cd7f6 100644
--- a/cortex-m-rt/Cargo.toml
+++ b/cortex-m-rt/Cargo.toml
@@ -42,10 +42,12 @@ name = "compiletest"
 required-features = ["device"]
 
 [features]
+default = ["hardfault-trampoline"]
 device = []
 set-sp = []
 set-vtor = []
 zero-init-ram = []
+hardfault-trampoline = ["cortex-m-rt-macros/hardfault-trampoline"]
 
 [package.metadata.docs.rs]
 features = ["device"]
diff --git a/cortex-m-rt/macros/Cargo.toml b/cortex-m-rt/macros/Cargo.toml
index f548e19..287ad9c 100644
--- a/cortex-m-rt/macros/Cargo.toml
+++ b/cortex-m-rt/macros/Cargo.toml
@@ -21,3 +21,6 @@ proc-macro2 = "1.0"
 [dependencies.syn]
 features = ["extra-traits", "full"]
 version = "2.0"
+
+[features]
+hardfault-trampoline = []
diff --git a/cortex-m-rt/macros/src/lib.rs b/cortex-m-rt/macros/src/lib.rs
index 27ee2f1..b529ef2 100644
--- a/cortex-m-rt/macros/src/lib.rs
+++ b/cortex-m-rt/macros/src/lib.rs
@@ -232,7 +232,7 @@ pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
                 #f
             )
         }
-        Exception::HardFault => {
+        Exception::HardFault if cfg!(feature = "hardfault-trampoline") => {
             let valid_signature = f.sig.constness.is_none()
                 && f.vis == Visibility::Inherited
                 && f.sig.abi.is_none()
@@ -283,6 +283,39 @@ pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
                 #f
             )
         }
+        Exception::HardFault => {
+            let valid_signature = f.sig.constness.is_none()
+                && f.vis == Visibility::Inherited
+                && f.sig.abi.is_none()
+                && f.sig.inputs.len() == 0
+                && f.sig.generics.params.is_empty()
+                && f.sig.generics.where_clause.is_none()
+                && f.sig.variadic.is_none()
+                && match f.sig.output {
+                    ReturnType::Default => false,
+                    ReturnType::Type(_, ref ty) => matches!(**ty, Type::Never(_)),
+                };
+
+            if !valid_signature {
+                return parse::Error::new(
+                    fspan,
+                    "`HardFault` handler must have signature `unsafe fn() -> !`",
+                )
+                .to_compile_error()
+                .into();
+            }
+
+            f.sig.ident = Ident::new(&format!("__cortex_m_rt_{}", f.sig.ident), Span::call_site());
+
+            quote!(
+                #[export_name = "HardFault"]
+                // Only emit link_section when building for embedded targets,
+                // because some hosted platforms (used to check the build)
+                // cannot handle the long link section names.
+                #[cfg_attr(target_os = "none", link_section = ".HardFault.user")]
+                #f
+            )
+        }
         Exception::NonMaskableInt | Exception::Other => {
             let valid_signature = f.sig.constness.is_none()
                 && f.vis == Visibility::Inherited
diff --git a/cortex-m-rt/src/lib.rs b/cortex-m-rt/src/lib.rs
index a6d946c..a39d32a 100644
--- a/cortex-m-rt/src/lib.rs
+++ b/cortex-m-rt/src/lib.rs
@@ -458,7 +458,7 @@ use core::fmt;
 // HardFault exceptions are bounced through this trampoline which grabs the stack pointer at
 // the time of the exception and passes it to the user's HardFault handler in r0.
 // Depending on the stack mode in EXC_RETURN, fetches stack from either MSP or PSP.
-#[cfg(cortex_m)]
+#[cfg(all(cortex_m, feature = "hardfault-trampoline"))]
 global_asm!(
     ".cfi_sections .debug_frame
      .section .HardFaultTrampoline, \"ax\"
@@ -1061,6 +1061,7 @@ pub static __RESET_VECTOR: unsafe extern "C" fn() -> ! = Reset;
 #[allow(unused_variables)]
 #[doc(hidden)]
 #[cfg_attr(cortex_m, link_section = ".HardFault.default")]
+#[cfg(feature = "hardfault-trampoline")]
 #[no_mangle]
 pub unsafe extern "C" fn HardFault_(ef: &ExceptionFrame) -> ! {
     #[allow(clippy::empty_loop)]
@@ -1068,6 +1069,15 @@ pub unsafe extern "C" fn HardFault_(ef: &ExceptionFrame) -> ! {
 }
 
 #[doc(hidden)]
+#[cfg_attr(cortex_m, link_section = ".HardFault.default")]
+#[cfg(not(feature = "hardfault-trampoline"))]
+#[no_mangle]
+pub unsafe extern "C" fn HardFault_() -> ! {
+    #[allow(clippy::empty_loop)]
+    loop {}
+}
+
+#[doc(hidden)]
 #[no_mangle]
 pub unsafe extern "C" fn DefaultHandler_() -> ! {
     #[allow(clippy::empty_loop)]
@@ -1115,7 +1125,10 @@ extern "C" {
 
     fn NonMaskableInt();
 
+    #[cfg(feature = "hardfault-trampoline")]
     fn HardFaultTrampoline();
+    #[cfg(not(feature = "hardfault-trampoline"))]
+    fn HardFault();
 
     #[cfg(not(armv6m))]
     fn MemoryManagement();
@@ -1154,9 +1167,12 @@ pub static __EXCEPTIONS: [Vector; 14] = [
         handler: NonMaskableInt,
     },
     // Exception 3: Hard Fault Interrupt.
+    #[cfg(feature = "hardfault-trampoline")]
     Vector {
         handler: HardFaultTrampoline,
     },
+    #[cfg(not(feature = "hardfault-trampoline"))]
+    Vector { handler: HardFault },
     // Exception 4: Memory Management Interrupt [not on Cortex-M0 variants].
     #[cfg(not(armv6m))]
     Vector {