Add non "inline_asm" impl for bochs_breakpoint

Signed-off-by: Joe Richey <[email protected]>

Author: josephlr

src/asm/asm.s

@@ -1,6 +1,10 @@
 .text
 .code64
 
+# REMEMBER: This code uses the AMD64 calling convention:
+#   Arguments: RDI, RSI, RDX, RCX
+#   Return: RAX
+
 .global _x86_64_asm_interrupt_enable
 .p2align 4
 _x86_64_asm_interrupt_enable:
@@ -249,6 +253,12 @@ _x86_64_asm_nop:
     nop
     retq
 
+.global _x86_64_asm_bochs
+.p2align 4
+_x86_64_asm_bochs:
+    xchgw %bx, %bx
+    retq
+
 .global _x86_64_asm_rdfsbase
 .p2align 4
 _x86_64_asm_rdfsbase:

src/asm/mod.rs

@@ -36,6 +36,12 @@ extern "C" {
     )]
     pub(crate) fn x86_64_asm_nop();
 
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_bochs"
+    )]
+    pub(crate) fn x86_64_asm_bochs();
+
     #[cfg_attr(
         any(target_env = "gnu", target_env = "musl"),
         link_name = "_x86_64_asm_read_from_port_u8"

src/instructions/mod.rs

@@ -40,11 +40,14 @@ pub fn nop() {
 
 /// Emits a '[magic breakpoint](https://wiki.osdev.org/Bochs#Magic_Breakpoint)' instruction for the [Bochs](http://bochs.sourceforge.net/) CPU
 /// emulator. Make sure to set `magic_break: enabled=1` in your `.bochsrc` file.
-#[cfg(feature = "inline_asm")]
 #[inline]
 pub fn bochs_breakpoint() {
     unsafe {
+        #[cfg(feature = "inline_asm")]
         asm!("xchg bx, bx", options(nomem, nostack, preserves_flags));
+
+        #[cfg(not(feature = "inline_asm"))]
+        crate::asm::x86_64_asm_bochs();
     }
 }