Merge pull request #535 from jannic/link_section

Add link_section = ".HardFault.user" to _HardFault

Author: adamgreig

cortex-m-rt/ci/script.sh

@@ -21,6 +21,7 @@ main() {
         divergent-default-handler
         divergent-exception
         entry-static
+        hard-fault-trampoline
         main
         minimal
         override-exception

cortex-m-rt/examples/hard-fault-trampoline.rs

@@ -0,0 +1,31 @@
+//! This is not an example; this is a linker test that ensures
+//! that the jump from HardFault to _HardFault doesn't exceed
+//! the 2kB limit of the branch instruction.
+
+#![deny(warnings)]
+#![no_main]
+#![no_std]
+
+extern crate cortex_m_rt;
+extern crate panic_halt;
+
+use core::arch::asm;
+use cortex_m_rt::{entry, exception, ExceptionFrame};
+
+// This defines both `HardFault` and `_HardFault`. Both should have
+// link_section attributes placing them at the end of the .text section,
+// close to each other. If one of them is missing that attribute, they
+// will end up separated by `foo`, which will make the linker fail.
+#[exception(trampoline = true)]
+unsafe fn HardFault(_ef: &ExceptionFrame) -> ! {
+    loop {}
+}
+
+#[entry]
+fn foo() -> ! {
+    unsafe {
+        // 2kB of NOP instructions to make the function artificially larger
+        asm!(".fill 1024,2,0xbf00",);
+    }
+    loop {}
+}

cortex-m-rt/macros/src/lib.rs

@@ -368,6 +368,10 @@ pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
                     #(#attrs)*
                     #[doc(hidden)]
                     #[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")]
                     unsafe extern "C" fn #tramp_ident(frame: &::cortex_m_rt::ExceptionFrame) {
                         #ident(frame)
                     }
@@ -379,7 +383,7 @@ pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
                     // Depending on the stack mode in EXC_RETURN, fetches stack from either MSP or PSP.
                     core::arch::global_asm!(
                         ".cfi_sections .debug_frame
-                        .section .HardFault.user, \"ax\"
+                        .section .HardFaultTrampoline, \"ax\"
                         .global HardFault
                         .type HardFault,%function
                         .thumb_func