From 1590e7c061898d23f3f8647b41d86b36aa148ad3 Mon Sep 17 00:00:00 2001
From: Duncan Ogilvie <mr.exodia.tpodt@gmail.com>
Date: Mon, 27 Apr 2026 03:39:34 +0200
Subject: [PATCH] [core] GDB improvements (#3848)

The commands to reproduce the issues are in the commit messages. I tested on Super Mario Odyssey using [nx2elf](https://github.com/shuffle2/nx2elf) converted binaries and gdb-multiarch:

```
(gdb) monitor info
Process:     0x51 (Application)
Program Id:  0x0100000000010000
Layout:
  Alias: 0x1103400000 - 0x21033fffff
  Heap:  0x2103400000 - 0x23033fffff
  Aslr:  0x0008000000 - 0x7fffffffff
  Stack: 0x1083400000 - 0x11033fffff
Modules:
  0x0080b3d000 - 0x0080b40fff nnrtld
  0x0080b41000 - 0x0081ff1fff RedStar.nss
  0x0081ff2000 - 0x008270efff multimedia
  0x008270f000 - 0x00833e2fff nnSdk
(gdb) monitor mappings
Mappings:
  0x0000000000 - 0x0080b3cfff     Free ----- [0, 0]
  0x0080b3d000 - 0x0080b3efff r-x Code ----- [0, 0]
  0x0080b3f000 - 0x0080b3ffff r-- Code ----- [0, 0]
  0x0080b40000 - 0x0080b40fff rw- CodeData ----- [0, 0]
  0x0080b41000 - 0x008156bfff r-x Code ----- [0, 0]
  0x008156c000 - 0x0081cdafff r-- Code ----- [0, 0]
  0x0081cdb000 - 0x0081ff1fff rw- CodeData ----- [0, 0]
  0x0081ff2000 - 0x0082365fff r-x Code ----- [0, 0]
  0x0082366000 - 0x00825c0fff r-- Code ----- [0, 0]
  0x00825c1000 - 0x008270efff rw- CodeData ----- [0, 0]
  0x008270f000 - 0x0082c3cfff r-x Code ----- [0, 0]
  0x0082c3d000 - 0x00832bffff r-- Code ----- [0, 0]
  0x00832c0000 - 0x00833e2fff rw- CodeData ----- [0, 0]
  0x00833e3000 - 0x0083403fff     Free ----- [0, 0]
  0x0083404000 - 0x0083404fff rw- ThreadLocal ----- [0, 0]
  0x0083405000 - 0x1083403fff     Free ----- [0, 0]
  0x1083404000 - 0x1083503fff rw- Stack ----- [0, 0]
  0x1083504000 - 0x7fffffffff     Free ----- [0, 0]
(gdb) set sysroot
(gdb) set solib-search-path /Users/duncan/Downloads/smo-program
Reading symbols from /Users/duncan/Downloads/smo-program/rtld.elf...
(No debugging symbols found in /Users/duncan/Downloads/smo-program/rtld.elf)
Reading symbols from /Users/duncan/Downloads/smo-program/main.elf...
(No debugging symbols found in /Users/duncan/Downloads/smo-program/main.elf)
Reading symbols from /Users/duncan/Downloads/smo-program/subsdk0.elf...
(No debugging symbols found in /Users/duncan/Downloads/smo-program/subsdk0.elf)
Reading symbols from /Users/duncan/Downloads/smo-program/sdk.elf...
(No debugging symbols found in /Users/duncan/Downloads/smo-program/sdk.elf)
(gdb) info shared
From                To                  Syms Read   Shared Object Library
0x0000000080b3d000  0x0000000080b41000  Yes (*)     /Users/duncan/Downloads/smo-program/rtld.elf
0x0000000080b41000  0x0000000081ff2000  Yes (*)     /Users/duncan/Downloads/smo-program/main.elf
0x0000000081ff2000  0x000000008270f000  Yes (*)     /Users/duncan/Downloads/smo-program/subsdk0.elf
0x000000008270f000  0x00000000833e3000  Yes (*)     /Users/duncan/Downloads/smo-program/sdk.elf
(*): Shared library is missing debugging information.
(gdb) info functions nnMain
All functions matching regular expression "nnMain":

Non-debugging symbols:
0x0000000081024250  nnMain
0x0000000082c2de40  nnMain@plt
(gdb) b *nnMain
Breakpoint 1 at 0x81024250
(gdb) c
Continuing.

Breakpoint 1, 0x0000000081024250 in nnMain () from /Users/duncan/Downloads/smo-program/main.elf
(gdb) x/10i $pc
=> 0x81024250 <nnMain>:	stp	x22, x21, [sp, #-48]!
   0x81024254 <nnMain+4>:	stp	x20, x19, [sp, #16]
   0x81024258 <nnMain+8>:	stp	x29, x30, [sp, #32]
   0x8102425c <nnMain+12>:	add	x29, sp, #0x20
   0x81024260 <nnMain+16>:	bl	0x81569aa0
   0x81024264 <nnMain+20>:	mov	w19, w0
   0x81024268 <nnMain+24>:	bl	0x81569ab0
   0x8102426c <nnMain+28>:	mov	x20, x0
   0x81024270 <nnMain+32>:	mov	w0, w19
   0x81024274 <nnMain+36>:	mov	x1, x20
```

Symlinked like this:

```
ls -l /Users/duncan/Downloads/smo-program
total 687472
-rw-r--r--@ 1 duncan  staff   20385356 Apr  9 18:12 main.elf
lrwxr-xr-x@ 1 duncan  staff         11 Apr  9 15:26 multimedia -> subsdk0.elf
lrwxr-xr-x@ 1 duncan  staff          8 Apr  9 15:28 nnrtld -> rtld.elf
lrwxr-xr-x@ 1 duncan  staff          7 Apr  9 15:26 nnSdk -> sdk.elf
lrwxr-xr-x@ 1 duncan  staff          8 Apr  9 15:26 RedStar.nss -> main.elf
-rw-r--r--@ 1 duncan  staff      12440 Apr  9 18:12 rtld.elf
-rw-r--r--@ 1 duncan  staff   12662960 Apr  9 18:12 sdk.elf
-rw-r--r--@ 1 duncan  staff    6294336 Apr  9 18:12 subsdk0.elf
```

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3848
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: crueter <crueter@eden-emu.dev>
---
 src/core/debugger/gdbstub_arch.cpp    |  4 ++--
 src/core/hle/kernel/physical_core.cpp | 28 ++++++++++++++++++++++-----
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/src/core/debugger/gdbstub_arch.cpp b/src/core/debugger/gdbstub_arch.cpp
index fec75c3432..5c5f3e8704 100644
--- a/src/core/debugger/gdbstub_arch.cpp
+++ b/src/core/debugger/gdbstub_arch.cpp
@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: Copyright 2022 yuzu Emulator Project
@@ -283,7 +283,7 @@ std::string_view GDBStubA32::GetTargetXML() const {
     <reg name="r11" bitsize="32" type="uint32"/>
     <reg name="r12" bitsize="32" type="uint32"/>
     <reg name="sp" bitsize="32" type="data_ptr"/>
-    <reg name="lr" bitsize="32" type="code_ptr"/>
+    <reg name="lr" bitsize="32"/>
     <reg name="pc" bitsize="32" type="code_ptr"/>
     <!-- The CPSR is register 25, rather than register 16, because
          the FPA registers historically were placed between the PC
diff --git a/src/core/hle/kernel/physical_core.cpp b/src/core/hle/kernel/physical_core.cpp
index e4aff43d82..f394122764 100644
--- a/src/core/hle/kernel/physical_core.cpp
+++ b/src/core/hle/kernel/physical_core.cpp
@@ -50,6 +50,14 @@ void PhysicalCore::RunThread(Kernel::KThread* thread) {
     };
 
     const auto ExitContext = [&]() {
+        // Save the JIT context back to the thread so the debugger can
+        // read the current register state. Debug halt paths (step,
+        // breakpoint, watchpoint) return from RunThread without going
+        // through the scheduler's Unload/SaveContext.
+        if (system.DebuggerEnabled()) {
+            interface->GetContext(thread->GetContext());
+        }
+
         // Unlock the thread.
         interface->UnlockThread(thread);
 
@@ -97,11 +105,16 @@ void PhysicalCore::RunThread(Kernel::KThread* thread) {
         }
 
         // Determine why we stopped.
-        const bool supervisor_call = True(hr & Core::HaltReason::SupervisorCall);
-        const bool prefetch_abort = True(hr & Core::HaltReason::PrefetchAbort);
-        const bool breakpoint = True(hr & Core::HaltReason::InstructionBreakpoint);
-        const bool data_abort = True(hr & Core::HaltReason::DataAbort);
-        const bool interrupt = True(hr & Core::HaltReason::BreakLoop);
+        // If a step completed successfully, skip other halt reason handlers —
+        // the step takes priority (e.g. step may also set InstructionBreakpoint
+        // if the next instruction happens to be a breakpoint).
+        const bool step_completed = True(hr & Core::HaltReason::StepThread)
+                                    && thread->GetStepState() == StepState::StepPerformed;
+        const bool supervisor_call = !step_completed && True(hr & Core::HaltReason::SupervisorCall);
+        const bool prefetch_abort = !step_completed && True(hr & Core::HaltReason::PrefetchAbort);
+        const bool breakpoint = !step_completed && True(hr & Core::HaltReason::InstructionBreakpoint);
+        const bool data_abort = !step_completed && True(hr & Core::HaltReason::DataAbort);
+        const bool interrupt = !step_completed && True(hr & Core::HaltReason::BreakLoop);
 
         // Since scheduling may occur here, we cannot use any cached
         // state after returning from calls we make.
@@ -111,6 +124,11 @@ void PhysicalCore::RunThread(Kernel::KThread* thread) {
         if (breakpoint || prefetch_abort) {
             if (breakpoint) {
                 interface->RewindBreakpointInstruction();
+                // RewindBreakpointInstruction sets the JIT state to the
+                // saved breakpoint context. Update the thread context to
+                // match, since ExitContext already saved the post-execution
+                // state.
+                interface->GetContext(thread->GetContext());
             }
             if (system.DebuggerEnabled()) {
                 system.GetDebugger().NotifyThreadStopped(thread);