10000 Fixed "jc fail" instructions not working properly and updated README.md by spencer3035 · Pull Request #453 · rust-osdev/bootloader · GitHub
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Fixed "jc fail" instructions not working properly and updated README.md #453

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Merged
merged 2 commits into from
Aug 25, 2024
Merged

Fixed "jc fail" instructions not working properly and updated README.md #453

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81f359d
Fixed "jc fail" instructions not working properly and updated README.md
spencer3035 Aug 21, 2024
8bc7a49
Fixed stage 2 fail calls and removed additional asm label
spencer3035 Aug 25, 2024
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Fixed stage 2 fail calls and removed additional asm label
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@spencer3035
spencer3035 committed Aug 25, 2024
commit 8bc7a49fcf5f9ea9b1ba003cf45e2ffd6eccdb99
2 changes: 1 addition & 1 deletion bios/boot_sector/README.md
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Expand Up @@ -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:

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7 changes: 3 additions & 4 deletions bios/boot_sector/src/boot.s
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Expand Up @@ -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:
Expand All @@ -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:
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4 changes: 3 additions & 1 deletion bios/boot_sector/src/dap.rs
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Expand Up @@ -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,
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6 changes: 4 additions & 2 deletions bios/stage-2/src/dap.rs
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Expand Up @@ -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,
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