Add support for AArch64

Add a stub for the arch (currently only works with a local branch).

Add the result of my observation to the README.

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>

Cargo.toml

@@ -6,6 +6,7 @@ edition = "2018"
 [features]
 default = []
 
+stub_aarch64 = []
 stub_arm = []
 stub_x86 = []
 stub_mips = []

README.md

@@ -96,6 +96,7 @@ See the `try_stepi.gdb` script for more commands.
 
 |        | `--single-step` (`vCont;c;C;s;S`) | (no support) (`vCont;c;C`) |
 |:------:|:---------------------------------:|:--------------------------:|
+|`aarch64`|      `vCont;s:p1.1;c:p1.-1`      |   `vCont;s:p1.1;c:p1.-1`   |
 |  `arm` |          `vCont;c:p1.-1`          |   `vCont;s:p1.1;c:p1.-1`   |
 | `mips` |          `vCont;c:p1.-1`          |       `vCont;c:p1.-1`      |
 |  `x86` |       `vCont;s:p1.1;c:p1.-1`      |   `vCont;s:p1.1;c:p1.-1`   |
@@ -105,6 +106,7 @@ See the `try_stepi.gdb` script for more commands.
   - This matches the spec.
 - The x86 example does _not_ work as expected.
   - If `--single-step` is not provided, the GDB stub reports `vCont;c;C`, and the GDB client nonetheless respond with `vCont;s:p1.1;c:p1.-1`! This results in a internal `gdbstub` error, and the example terminates.
+- The AArch64 example also assumes support for `vCont`.
 - The MIPS example is interesting.
   - Regardless if `--single-step` was provided, the GDB client will _never_ send a `vCont;s:pX.X` packet!
   - While this isn't strictly an "error", it is nonetheless weird that the GDB client doesn't attempt to use the target's "native" single step feature.

check_vcont.sh

@@ -8,7 +8,7 @@ function run_test {
 	${gdb} -x try_stepi.gdb -ex quit &>/dev/null
 	kill ${cargo} &>/dev/null
 }
-declare -A supported_archs=([arm]= [mips]= [x86]=)
+declare -A supported_archs=([aarch64]= [arm]= [mips]= [x86]=)
 
 export RUST_LOG="error,gdbstub::protocol=trace"
 

src/gdb_aarch64.rs

@@ -0,0 +1,108 @@
+use gdbstub::arch::{Arch, SingleStepGdbBehavior};
+use gdbstub::common::Signal;
+use gdbstub::target;
+use gdbstub::target::ext::base::singlethread::{SingleThreadBase, SingleThreadResume};
+use gdbstub::target::{Target, TargetResult};
+
+use crate::emu::{Emu, ExecMode};
+
+impl Target for Emu<u64> {
+    type Arch = gdbstub_arch::aarch64::AArch64;
+    type Error = &'static str;
+
+    #[inline(always)]
+    fn base_ops(&mut self) -> target::ext::base::BaseOps<Self::Arch, Self::Error> {
+        target::ext::base::BaseOps::SingleThread(self)
+    }
+
+    #[inline(always)]
+    fn guard_rail_implicit_sw_breakpoints(&self) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn guard_rail_single_step_gdb_behavior(&self) -> SingleStepGdbBehavior {
+        if !self.with_guard_rail {
+            SingleStepGdbBehavior::Optional
+        } else {
+            Self::Arch::single_step_gdb_behavior()
+        }
+    }
+}
+
+impl SingleThreadResume for Emu<u64> {
+    fn resume(&mut self, signal: Option<Signal>) -> Result<(), Self::Error> {
+        if signal.is_some() {
+            return Err("no support for continuing with signal");
+        }
+
+        self.exec_mode = ExecMode::Continue;
+
+        Ok(())
+    }
+
+    #[inline(always)]
+    fn support_single_step(
+        &mut self,
+    ) -> Option<target::ext::base::singlethread::SingleThreadSingleStepOps<Self>> {
+        if self.with_single_step {
+            Some(self)
+        } else {
+            None
+        }
+    }
+}
+
+impl SingleThreadBase for Emu<u64> {
+    fn read_registers(
+        &mut self,
+        regs: &mut gdbstub_arch::aarch64::reg::AArch64CoreRegs,
+    ) -> TargetResult<(), Self> {
+        log::debug!("read_registers");
+
+        for (i, reg) in regs.x.iter_mut().enumerate() {
+            *reg = i as u64;
+        }
+        regs.pc = 0x5555_0000;
+
+        Ok(())
+    }
+
+    fn write_registers(
+        &mut self,
+        regs: &gdbstub_arch::aarch64::reg::AArch64CoreRegs,
+    ) -> TargetResult<(), Self> {
+        log::debug!("write_registers: {:#x?}", regs);
+        Ok(())
+    }
+
+    fn read_addrs(&mut self, start_addr: u64, data: &mut [u8]) -> TargetResult<(), Self> {
+        log::debug!("read_addrs: {:#x?},{}", start_addr, data.len());
+        data.fill(0x00); // nop
+        Ok(())
+    }
+
+    fn write_addrs(&mut self, start_addr: u64, data: &[u8]) -> TargetResult<(), Self> {
+        log::debug!("write_addrs: {:#x?},{:x?}", start_addr, data);
+        Ok(())
+    }
+
+    #[inline(always)]
+    fn support_resume(
+        &mut self,
+    ) -> Option<target::ext::base::singlethread::SingleThreadResumeOps<'_, Self>> {
+        Some(self)
+    }
+}
+
+impl target::ext::base::singlethread::SingleThreadSingleStep for Emu<u64> {
+    fn step(&mut self, signal: Option<Signal>) -> Result<(), Self::Error> {
+        if signal.is_some() {
+            return Err("no support for stepping with signal");
+        }
+
+        self.exec_mode = ExecMode::Step;
+
+        Ok(())
+    }
+}

src/main.rs

@@ -10,20 +10,25 @@ use gdbstub::target::Target;
 
 mod emu;
 
+#[cfg(feature = "stub_aarch64")]
+mod gdb_aarch64;
 #[cfg(feature = "stub_arm")]
 mod gdb_arm;
 #[cfg(feature = "stub_mips")]
 mod gdb_mips;
 #[cfg(feature = "stub_x86")]
 mod gdb_x86;
 #[cfg(not(any(
+    feature = "stub_aarch64",
     feature = "stub_arm",
     feature = "stub_mips",
     feature = "stub_x86",
 )))]
 #[rustfmt::skip]
 compile_error!(concat!(
     "must compile with one --feature from [",
+    "stub_aarch64",
+    ", ",
     "stub_arm",
     ", ",
     "stub_mips",