Fixed stage 2 fail calls and removed additional asm label

Author: spencer3035

bios/boot_sector/README.md

@@ -9,7 +9,7 @@ This executable needs to fit into the 512-byte boot sector, so we need to use al
 
 To run in QEMU:
 
-- `qemu-system-x86_64 -drive format=raw,file=../../target/disk_image.bin`
+- `qemu-system-x86_64 -drive format=raw,file=../../target/disk_image.img`
 
 To print the contents of the ELF file, e.g. for trying to bring the size down:
 

bios/boot_sector/src/boot.s

@@ -36,7 +36,9 @@ check_int13h_extensions:
     mov bx, 0x55aa
     # dl contains drive number
     int 0x13
-    jc fail_asm
+    jnc .int13_pass
+    call fail
+.int13_pass:
     pop ax      # pop error code again
 
 rust:
@@ -45,9 +47,6 @@ rust:
     call first_stage
     # Fail code if first stage returns
     push 'x'
-
-    # Call rust "fail" function that prints the character on the top of the stack
-fail_asm:
     call fail
 
 spin:

bios/boot_sector/src/dap.rs

@@ -42,7 +42,9 @@ impl DiskAddressPacket {
                 "mov {1:x}, si", // backup the `si` register, whose contents are required by LLVM
                 "mov si, {0:x}",
                 "int 0x13",
-                "jc fail_asm",
+                "jnc 2f", // carry is set on fail
+                "call fail",
+                "2:",
                 "pop si", // remove error code again
                 "mov si, {1:x}", // restore the `si` register to its prior state
                 in(reg) self_addr,

bios/stage-2/src/dap.rs

@@ -38,11 +38,13 @@ impl DiskAddressPacket {
     pub unsafe fn perform_load(&self, disk_number: u16) {
         let self_addr = self as *const Self as u16;
         asm!(
-            "push 0x7a", // error code `z`, passed to `fail` on error
+            "push 'z'", // error code `z`, passed to `fail` on error
             "mov {1:x}, si",
             "mov si, {0:x}",
             "int 0x13",
-            "jc fail",
+            "jnc 2f", // carry is set on fail
+            "call fail",
+            "2:",
             "pop si", // remove error code again
             "mov si, {1:x}",
             in(reg) self_addr,