From b0ecc260021fb2d1e848f46baaf2c488f799de4f Mon Sep 17 00:00:00 2001
From: Sean Cross <sean@xobs.io>
Date: Thu, 11 May 2023 15:13:03 +0800
Subject: [PATCH] kernel: gdb: batch 2- and 4-byte accesses

Instead of always doing bytewise accesses, support 2- and 4-byte access.
Additionally, recognize when multiple 4-byte reads are required.

Note that an additional optimization may be made here in the future to
prevent having to check every address, but this is left for a future
optimization.

Signed-off-by: Sean Cross <sean@xobs.io>
---
 kernel/src/debug/gdb/multi_thread_base.rs | 54 ++++++++++++++++++-----
 1 file changed, 43 insertions(+), 11 deletions(-)

diff --git a/kernel/src/debug/gdb/multi_thread_base.rs b/kernel/src/debug/gdb/multi_thread_base.rs
index 7d1226c23..6a9bbb844 100644
--- a/kernel/src/debug/gdb/multi_thread_base.rs
+++ b/kernel/src/debug/gdb/multi_thread_base.rs
@@ -5,6 +5,7 @@ use gdbstub::target::ext::base::single_register_access::SingleRegisterAccessOps;
 use gdbstub::target::TargetResult;
 
 use super::XousTarget;
+use core::convert::TryInto;
 
 impl MultiThreadBase for XousTarget {
     fn read_registers(
@@ -107,10 +108,33 @@ impl MultiThreadBase for XousTarget {
                 .unwrap()
                 .activate()
                 .unwrap();
-            for (offset, b) in data.iter_mut().enumerate() {
-                *b = crate::arch::mem::peek_memory((current_addr + offset) as *mut u8)
-                    .unwrap_or(0xff);
-                // println!("<< Peek {:02x} @ {:08x}", *b, current_addr);
+
+            if data.len() == 2 && (start_addr & 1) == 0 {
+                let val = crate::arch::mem::peek_memory(start_addr as *mut u16).unwrap_or(0);
+                for (dest, src) in data.iter_mut().zip(val.to_le_bytes()) {
+                    *dest = src;
+                }
+            } else if data.len() == 4 && (start_addr & 3) == 0 {
+                let val = crate::arch::mem::peek_memory(start_addr as *mut u32).unwrap_or(0);
+                for (dest, src) in data.iter_mut().zip(val.to_le_bytes()) {
+                    *dest = src;
+                }
+            } else if (data.len() & 3) == 0 && (start_addr & 3) == 0 {
+                let mut current_addr = current_addr;
+                for word in data.chunks_mut(4) {
+                    let bytes = crate::arch::mem::peek_memory(current_addr as *mut u32)
+                        .unwrap_or(0)
+                        .to_le_bytes();
+                    for (dest, src) in word.iter_mut().zip(bytes) {
+                        *dest = src;
+                    }
+                    current_addr += 4;
+                }
+            } else {
+                for (offset, b) in data.iter_mut().enumerate() {
+                    *b = crate::arch::mem::peek_memory((current_addr + offset) as *mut u8)
+                        .unwrap_or(0xff);
+                }
             }
 
             // Restore the previous PID
@@ -145,13 +169,21 @@ impl MultiThreadBase for XousTarget {
                 .unwrap()
                 .activate()
                 .unwrap();
-            data.iter().for_each(|b| {
-                if let Err(_e) = crate::arch::mem::poke_memory(current_addr as *mut u8, *b) {
-                    // panic!("couldn't poke memory: {:?}", _e);
-                }
-                // println!("Poked {:02x} @ {:08x}", *b, current_addr);
-                current_addr += 1;
-            });
+
+            if data.len() == 2 && (start_addr & 1) == 0 {
+                let val = u16::from_le_bytes(data.try_into().unwrap());
+                crate::arch::mem::poke_memory(start_addr as *mut u16, val).ok();
+            } else if data.len() == 4 && (start_addr & 3) == 0 {
+                let val = u32::from_le_bytes(data.try_into().unwrap());
+                crate::arch::mem::poke_memory(start_addr as *mut u32, val).ok();
+            } else {
+                data.iter().for_each(|b| {
+                    if let Err(_e) = crate::arch::mem::poke_memory(current_addr as *mut u8, *b) {
+                        // panic!("couldn't poke memory: {:?}", _e);
+                    }
+                    current_addr += 1;
+                });
+            }
 
             // Restore the previous PID
             system_services