From 12ee6e502e357529ccbd4f99e9627ca1b501e5ef Mon Sep 17 00:00:00 2001
From: yellows8 <yellows8@users.noreply.github.com>
Date: Wed, 14 Nov 2018 20:55:17 -0500
Subject: [PATCH] Fixed register corruption in crt0 introduced by the exception
 commit. Only handle exceptions when __libnx_exception_handler is defined by
 the user, and updated comments.

---
 nx/source/runtime/exception.s   |  8 ++++++++
 nx/source/runtime/init.c        |  9 ++++-----
 nx/source/runtime/switch_crt0.s | 10 +++++++---
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/nx/source/runtime/exception.s b/nx/source/runtime/exception.s
index e7f6a522..54cc4d0e 100644
--- a/nx/source/runtime/exception.s
+++ b/nx/source/runtime/exception.s
@@ -13,11 +13,19 @@
 
 // Called by crt0 when the args at the time of entry indicate an exception occured.
 
+.weak __libnx_exception_handler
+
 .weak __libnx_exception_entry
 CODE_BEGIN __libnx_exception_entry
     cmp x1, #0
     beq __libnx_exception_entry_abort
 
+    // Abort exception handling when __libnx_exception_handler is not defined.
+    adrp x5, :got:__libnx_exception_handler
+    ldr x5, [x5, #:got_lo12:__libnx_exception_handler]
+    cmp x5, #0
+    beq __libnx_exception_entry_abort
+
     // Load IsCurrentProcessBeingDebugged.
 
     stp x9, x10, [sp, #-16]!
diff --git a/nx/source/runtime/init.c b/nx/source/runtime/init.c
index 0a4ea64f..d214c177 100644
--- a/nx/source/runtime/init.c
+++ b/nx/source/runtime/init.c
@@ -21,12 +21,15 @@ extern u32 __nx_applet_type;
 // Must be a multiple of 0x200000.
 __attribute__((weak)) size_t __nx_heap_size = 0;
 
-/// Override these with your own if you're using __libnx_exception_handler. __nx_exception_stack is the stack-bottom.
+/// Override these with your own if you're using \ref__libnx_exception_handler. __nx_exception_stack is the stack-bottom. Update \ref __nx_exception_stack_size if you change this.
 __attribute__((weak)) alignas(16) u8 __nx_exception_stack[0x400];
 __attribute__((weak)) u64 __nx_exception_stack_size = sizeof(__nx_exception_stack);
 /// By default exception handling will be aborted when the current process is being debugged. Set this to non-zero to disable that.
 __attribute__((weak)) u32 __nx_exception_ignoredebug = 0;
 
+/// Override this with your own func to handle exceptions. See \ref __nx_exception_stack. See here: https://switchbrew.org/wiki/SVC#Exception_handling
+void __attribute__((weak)) __libnx_exception_handler(ThreadExceptionDump *ctx);
+
 ThreadExceptionDump __nx_exceptiondump;
 
 /*
@@ -175,7 +178,3 @@ void __attribute__((weak)) NORETURN __libnx_exit(int rc)
     __nx_exit(0, envGetExitFuncPtr());
 }
 
-/// You can override this with your own func to handle exceptions. See here: https://switchbrew.org/wiki/SVC#Exception_handling
-void __attribute__((weak)) __libnx_exception_handler(ThreadExceptionDump *ctx)
-{
-}
diff --git a/nx/source/runtime/switch_crt0.s b/nx/source/runtime/switch_crt0.s
index c06df8fb..4f6f1fb2 100644
--- a/nx/source/runtime/switch_crt0.s
+++ b/nx/source/runtime/switch_crt0.s
@@ -27,6 +27,10 @@ startup:
     b __libnx_exception_entry
 
 bssclr_start:
+    mov x27, x7
+    mov x25, x5
+    mov x26, x4
+
     // clear .bss
     adrp x0, __bss_start__
     adrp x1, __bss_end__
@@ -53,9 +57,9 @@ bss_loop:
     bl   __nx_dynamic
 
     // initialize system
-    mov  x0, x5
-    mov  x1, x4
-    mov  x2, x7
+    mov  x0, x25
+    mov  x1, x26
+    mov  x2, x27
     bl   __libnx_init
 
     // call entrypoint