Allow Target to override Arch's target description

src/gdbstub_impl/mod.rs

@@ -303,7 +303,9 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                 // TODO: implement conditional breakpoint support (since that's kool).
                 // res.write_str("ConditionalBreakpoints+;")?;
 
-                if T::Arch::target_description_xml().is_some() {
+                if target.target_description().is_some()
+                    || <T::Arch as Arch>::target_description_xml().is_some()
+                {
                     res.write_str(";qXfer:features:read+")?;
                 }
 
@@ -314,7 +316,17 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                 HandlerStatus::NeedsOK
             }
             ext::Base::qXferFeaturesRead(cmd) => {
-                match T::Arch::target_description_xml() {
+                // Query the target description ops for the target's description.
+                let xml = {
+                    // Target gets the first chance to override the XML description.
+                    target
+                        .target_description()
+                        .map_or(<T::Arch as Arch>::target_description_xml(), |v| {
+                            Some(v.target_description_xml())
+                        })
+                };
+
+                match xml {
                     Some(xml) => {
                         let xml = xml.trim();
                         if cmd.offset >= xml.len() {
@@ -331,10 +343,11 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                         }
                     }
                     // If the target hasn't provided their own XML, then the initial response to
-                    // "qSupported" wouldn't have included  "qXfer:features:read", and gdb wouldn't
-                    // send this packet unless it was explicitly marked as supported.
+                    // "qSupported" wouldn't have included  "qXfer:features:read", and gdb
+                    // wouldn't send this packet unless it was explicitly marked as supported.
                     None => return Err(Error::PacketUnexpected),
                 }
+
                 HandlerStatus::Handled
             }
 

src/target/ext/base/description.rs

@@ -0,0 +1,15 @@
+use crate::arch::Arch;
+use crate::target::Target;
+
+/// Basic operation to return an XML-formatted target description string
+/// to the GDB client.
+pub trait TargetDescription: Target {
+    /// Returns an optional XML description for the target to GDB.
+    fn target_description_xml(&self) -> &'static str {
+        <Self::Arch as Arch>::target_description_xml().unwrap()
+    }
+}
+
+/// See [`TargetDescription`]
+pub type TargetDescriptionOps<'a, T> =
+    &'a mut dyn TargetDescription<Arch = <T as Target>::Arch, Error = <T as Target>::Error>;

src/target/ext/base/mod.rs

@@ -7,6 +7,11 @@
 pub mod multithread;
 pub mod singlethread;
 
+mod description;
+
+pub use description::TargetDescription;
+pub use description::TargetDescriptionOps;
+
 /// Base operations for single/multi threaded targets.
 pub enum BaseOps<'a, A, E> {
     /// Single-threaded target

src/target/mod.rs

@@ -239,6 +239,11 @@ pub trait Target {
     fn section_offsets(&mut self) -> Option<ext::section_offsets::SectionOffsetsOps<Self>> {
         None
     }
+
+    /// Handle requests for the target's XML description for GDB.
+    fn target_description(&mut self) -> Option<ext::base::TargetDescriptionOps<Self>> {
+        None
+    }
 }
 
 macro_rules! impl_dyn_target {