From 460166b74627651b08f685cf1bd3775e9207c9a9 Mon Sep 17 00:00:00 2001
From: mebibytedraco <139500397+mebibytedraco@users.noreply.github.com>
Date: Sun, 24 Dec 2023 20:43:47 -0500
Subject: [PATCH] Add '%' debug prefix to shell

---
 applications/sh/launch.asm | 45 +++++++++++++++++++++++++++++++++++---
 1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/applications/sh/launch.asm b/applications/sh/launch.asm
index 6548f23..7974502 100644
--- a/applications/sh/launch.asm
+++ b/applications/sh/launch.asm
@@ -15,13 +15,24 @@ launch_fxf:
     call copy_memory_bytes
     pop r0
 
+launch_fxf_check_suspend_prefix:
     ; if the name was prefixed with a '*' character then
     ; clear a flag to have the shell return control immediately
     cmp.8 [r0], '*'
     ifnz mov.8 [launch_fxf_yield_should_suspend], 1
-    ifnz jmp launch_fxf_no_prefix
+    ifnz jmp launch_fxf_check_debug_prefix
     inc r0
     mov.8 [launch_fxf_yield_should_suspend], 0
+    jmp launch_fxf_no_prefix
+launch_fxf_check_debug_prefix:
+    ; if the name was prefixed with a '%' character then
+    ; set a flag to cause a breakpoint at the beginning of the
+    ; program
+    cmp.8 [r0], '%'
+    ifnz mov.8 [launch_fxf_debug_mode], 0
+    ifnz jmp launch_fxf_no_prefix
+    inc r0
+    mov.8 [launch_fxf_debug_mode], 1
 launch_fxf_no_prefix:
     ; copy the name into the launch_fxf_name buffer
     mov r1, launch_fxf_name
@@ -66,6 +77,9 @@ launch_fxf_name_loop_done:
     ; push the argument pointers and terminal stream struct pointer to the task's stack
     call shell_parse_arguments
     mov r4, rsp
+    ; disable interrupts, because if an interrupt tried to use the stack
+    ; during this then that probably wouldn't end well
+    icl
     mov rsp, [launch_fxf_stack_ptr]
     add rsp, 65536 ; point to the end of the stack (stack grows down!!)
     push r3
@@ -73,13 +87,28 @@ launch_fxf_name_loop_done:
     push r1
     push r0
     push [shell_stream_struct_ptr]
-    sub rsp, 65516
-    mov [launch_fxf_stack_ptr], rsp
+    ; if we are in debug mode, push interrupt return info onto the stack
+    cmp.8 [launch_fxf_debug_mode], 0
+    ifz jmp launch_fxf_skip_push_reti_info
+    push 0 ; return address, will be filled in once we have start address
+    mov r1, rsp ; save address of return address to fill in later
+    push.8 0x04 ; enable interrupts upon return
+    push 0 ; don't care about exception parameter
+launch_fxf_skip_push_reti_info:
     mov rsp, r4
+    ise
 
     ; relocate the binary
     mov r0, [launch_fxf_binary_ptr]
     call parse_fxf_binary
+    ; if we are in debug mode, fill in the return adress with the relocation
+    ; address of the loaded binary
+    cmp.8 [launch_fxf_debug_mode], 0
+    ifz jmp launch_fxf_skip_fill_reti_addr
+    mov [r1], r0
+    ; set initial ip to launch_fxf_debug_start
+    mov r0, launch_fxf_debug_start
+launch_fxf_skip_fill_reti_addr:
 
     ; create a new task
     mov r1, r0
@@ -87,6 +116,9 @@ launch_fxf_name_loop_done:
     mov.8 [launch_fxf_task_id], r0
     mov r2, [launch_fxf_stack_ptr]
     add r2, 65516 ; point to the end of the stack (stack grows down!!)
+    ; if we are in debug mode, there are 9 extra bytes on top of the stack
+    cmp.8 [launch_fxf_debug_mode], 0
+    ifnz sub r2, 9
     mov r3, [launch_fxf_binary_ptr]
     mov r4, [launch_fxf_stack_ptr]
     call new_task
@@ -108,6 +140,12 @@ allocate_error:
     call print_str_to_terminal
     ret
 
+; entry point for a program started in debug mode
+launch_fxf_debug_start:
+    icl
+    ; jump indirect through system exception vector
+    jmp [0x00000410]
+
 launch_fxf_name: data.str "        fxf"
 launch_fxf_spaces: data.str "        "
 launch_fxf_struct: data.fill 0, 32
@@ -116,5 +154,6 @@ launch_fxf_binary_ptr: data.32 0
 launch_fxf_stack_ptr: data.32 0
 
 launch_fxf_yield_should_suspend: data.8 0
+launch_fxf_debug_mode: data.8 0
 
 out_of_memory_string: data.str "failed to allocate for new task!" data.8 10 data.8 0