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Commit ea3f61a

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spencer3035spencer3035
authored
Fixed "jc fail" instructions not working properly and updated README.md (#453)
* Fixed "jc fail" instructions not working properly and updated README.md * Fixed stage 2 fail calls and removed additional asm label
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‎bios/boot_sector/README.md

Copy file name to clipboardExpand all lines: bios/boot_sector/README.md
+4-4Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -4,13 +4,13 @@ This executable needs to fit into the 512-byte boot sector, so we need to use al
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## Build Commands
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7-
1. `cargo build --release -Zbuild-std=core --target x86-16bit.json -Zbuild-std-features=compiler-builtins-mem`
8-
2. `objcopy -I elf32-i386 -O binary target/x86-16bit/release/first_stage target/disk_image.bin
7+
1. `cargo build --profile=stage-1 -Zbuild-std=core --target ../../i386-code16-boot-sector.json -Zbuild-std-features=compiler-builtins-mem`
8+
2. `objcopy -I elf32-i386 -O binary ../../target/i386-code16-boot-sector/stage-1/bootloader-x86_64-bios-boot-sector ../../target/disk_image.img`
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To run in QEMU:
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12-
- `qemu-system-x86_64 -drive format=raw,file=target/disk_image.bin`
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- `qemu-system-x86_64 -drive format=raw,file=../../target/disk_image.img`
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To print the contents of the ELF file, e.g. for trying to bring the size down:
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16-
- `objdump -xsdS -M i8086,intel target/x86-16bit/release/first_stage`
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- `objdump -xsdS -M i8086,intel ../../target/i386-code16-boot-sector/stage-1/bootloader-x86_64-bios-boot-sector`

‎bios/boot_sector/src/boot.s

Copy file name to clipboardExpand all lines: bios/boot_sector/src/boot.s
+6-1Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -36,13 +36,18 @@ check_int13h_extensions:
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mov bx, 0x55aa
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# dl contains drive number
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int 0x13
39-
jc fail
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jnc .int13_pass
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call fail
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.int13_pass:
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pop ax # pop error code again
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rust:
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# push arguments
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push dx # disk number
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call first_stage
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# Fail code if first stage returns
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push 'x'
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call fail
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4752
spin:
4853
hlt

‎bios/boot_sector/src/dap.rs

Copy file name to clipboardExpand all lines: bios/boot_sector/src/dap.rs
+4-2Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -38,11 +38,13 @@ impl DiskAddressPacket {
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let self_addr = self as *const Self as u16;
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unsafe {
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asm!(
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"push 0x7a", // error code `z`, passed to `fail` on error
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"push 'z'", // error code `z`, passed to `fail` on error
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"mov {1:x}, si", // backup the `si` register, whose contents are required by LLVM
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"mov si, {0:x}",
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"int 0x13",
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"jc fail",
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"jnc 2f", // carry is set on fail
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"call fail",
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"2:",
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"pop si", // remove error code again
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"mov si, {1:x}", // restore the `si` register to its prior state
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in(reg) self_addr,

‎bios/boot_sector/src/mbr.rs

Copy file name to clipboardExpand all lines: bios/boot_sector/src/mbr.rs
+2-2Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -16,14 +16,14 @@ pub(crate) fn get_partition(partitions_raw: &[u8], index: usize) -> PartitionTab
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.get(8..)
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.and_then(|s| s.get(..4))
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.and_then(|s| s.try_into().ok())
19-
.unwrap_or_fail(b'e'),
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.unwrap_or_fail(b'f'),
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);
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let len = u32::from_le_bytes(
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buffer
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.get(12..)
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.and_then(|s| s.get(..4))
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.and_then(|s| s.try_into().ok())
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.unwrap_or_fail(b'f'),
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.unwrap_or_fail(b'g'),
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);
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PartitionTableEntry::new(bootable, partition_type, lba, len)
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}

‎bios/stage-2/src/dap.rs

Copy file name to clipboardExpand all lines: bios/stage-2/src/dap.rs
+4-2Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -38,11 +38,13 @@ impl DiskAddressPacket {
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pub unsafe fn perform_load(&self, disk_number: u16) {
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let self_addr = self as *const Self as u16;
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asm!(
41-
"push 0x7a", // error code `z`, passed to `fail` on error
41+
"push 'z'", // error code `z`, passed to `fail` on error
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"mov {1:x}, si",
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"mov si, {0:x}",
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"int 0x13",
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"jc fail",
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"jnc 2f", // carry is set on fail
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"call fail",
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"2:",
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"pop si", // remove error code again
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"mov si, {1:x}",
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in(reg) self_addr,

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