boot: convert paging from assembly to Zig (take 2)

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: install dependencies
-        run: sudo apt install -y nasm clang mtools
+        run: sudo apt install -y nasm clang mtools lld
 
       - name: install zig
         run: sudo snap install zig --classic --beta

Makefile

@@ -18,9 +18,25 @@ bin/kernel-userland.o: src/kernel/userland.asm | bin
 		-o $@ \
 		$<
 
-# -O ReleaseFast
-bin/boot_zig.o: src/boot/boot.zig | bin
-	zig build-obj -target x86_64-freestanding-gnu -static -I./src/kernel -mno-red-zone -femit-bin=$@ $<
+# NOTE: use `-fcompiler-rt` to include __zig_probe_stack symbol when linking
+# (see https://github.com/ziglang/zig/issues/6817).
+bin/%_32_zig.o: src/boot/%_32.zig | bin
+	@zig build-obj \
+		--cache-dir bin/zig-cache \
+		-I src/kernel \
+		-mno-red-zone \
+		-fcompiler-rt \
+		-static \
+		-target x86-freestanding-gnu \
+		-O Debug \
+		-mcpu=i386 \
+		-femit-bin=$@ \
+		$<
+
+# TODO: remove objcopy hack when we figure out a way to emit ELF64 objets
+# containing 32-bit code in Zig (NOTE: how is this done in C??).
+bin/%_elf64_zig.o: bin/%_32_zig.o
+	@objcopy --output-target elf64-x86-64 $< $@
 
 # --nmagic
 #     Turn off page alignment of sections, and disable linking against shared
@@ -31,8 +47,10 @@ bin/boot_zig.o: src/boot/boot.zig | bin
 # --no-warn-rwx-segments
 #     Allow use of RWX segments.
 
-bin/kernel.elf: bin/boot_zig.o bin/boot.o bin/kernel-userland.o bin/kernel.o bin/libhello.o bin/libfloof.a | bin
-	ld \
+# NOTE: using ld.lld instead of ld as work-around for bug in ld (for details,
+# see https://github.com/karlek/lappis/pull/19/commits/9cf1a8a7d40c21c6a23c1bb0412a7f49f3f1b211#r883015557).
+bin/kernel.elf: bin/boot_elf64_zig.o bin/paging_elf64_zig.o bin/boot.o bin/kernel-userland.o bin/kernel.o bin/libhello.o bin/libfloof.a | bin
+	ld.lld \
 		--nmagic \
 		--output $@ \
 		--script linker.ld \
@@ -43,8 +61,8 @@ bin/kernel.elf: bin/boot_zig.o bin/boot.o bin/kernel-userland.o bin/kernel.o bin
 # TODO: When ubuntu-latest on github actions is updated, add this to remove nag.
 # --no-warn-rwx-segments
 #     Allow use of RWX segments.
-bin/kernel.dbg: bin/boot_zig.o bin/boot.o bin/kernel-userland.o bin/kernel.o bin/libhello.o bin/libfloof.a | bin
-	ld \
+bin/kernel.dbg: bin/boot_elf64_zig.o bin/paging_elf64_zig.o bin/boot.o bin/kernel-userland.o bin/kernel.o bin/libhello.o bin/libfloof.a | bin
+	ld.lld \
 		--output $@ \
 		--script linker.ld \
 		$^
@@ -142,12 +160,6 @@ bin/zipfs.zip: fs/userland.elf | bin
 bin/zipfs.img: bin/zipfs.zip | bin
 	dd if=bin/zipfs.zip of=$@ bs=1M conv=sync
 
-bin/fat32.img: | bin
-	@dd if=/dev/zero of=$@ count=50 bs=1M conv=sync
-	@mkfs.vfat -F 32 $@
-	@mcopy -i $@ -s fs/* ::
-	@mdir -i $@ -s
-
 bin:
 	@mkdir -p $@
 
@@ -165,12 +177,12 @@ bin/libfloof.a: src/kernel/rust/src/lib.rs
 	cd src/kernel/rust; cargo build -Zbuild-std ; cargo build
 	mv src/kernel/rust/target/os/debug/libfloof.a bin
 
-build: bin/kernel.iso bin/kernel.dbg bin/zipfs.img bin/fat32.img
+build: bin/kernel.iso bin/kernel.dbg bin/zipfs.img
 
-debug: bin/kernel.iso bin/kernel.dbg bin/zipfs.img bin/fat32.img
+debug: bin/kernel.iso bin/kernel.dbg bin/zipfs.img
 	./debug.sh
 
-run: bin/kernel.iso bin/zipfs.img bin/fat32.img
+run: bin/kernel.iso bin/zipfs.img
 	./run.sh
 
 bin/kernel.iso: bin/kernel.elf grub.cfg | bin

debug.gdb

@@ -1,10 +1,11 @@
-source debug.py
-
 set disassembly-flavor intel
 
-target remote localhost:1234
 symbol-file bin/kernel.dbg
 
+source ../gef/gef.py
+source ../gdb-pt-dump/pt.py
+
+gef-remote --qemu-user localhost 1234
 # Any break points should be set here.
 # break main
 break enter_userland
@@ -13,8 +14,3 @@ break yay_userland
 
 # Run until the program first breakpoint.
 continue
-
-# Add break points that will be added after our first breakpoint has been hit.
-# break irq_timer
-# break *irq_timer+24
-# break not_implemented_0

debug.sh

@@ -1,32 +1,33 @@
 #!/bin/bash
 
-set -e
+set -ex
 
 cat /dev/null > /tmp/serial.log
 cat /dev/null > /tmp/serial.raw
-kitty --class lappis-serial-raw -e fish -c 'tail -f /tmp/serial.raw' &
+kitty --class lappis-serial-raw -e tail -f /tmp/serial.raw &
 kitty --class lappis-serial-log -e tail -f /tmp/serial.log &
-sleep 1
 
-kitty --class qemu-starter \
+kitty --class lappis-qemu \
 	qemu-system-x86_64 \
+	-cpu qemu64,+smep,+smap \
 	-no-reboot \
 	-no-shutdown \
 	-S \
 	-gdb tcp::1234 \
 	-d int \
-	-m size=128M \
+	-m size=4G \
 	-monitor stdio \
 	-serial file:/tmp/serial.log \
 	-serial file:/tmp/serial.raw \
 	-drive media=disk,index=0,file=bin/zipfs.img,format=raw,if=ide \
-	-drive media=disk,index=1,file=bin/fat32.img,format=raw,if=ide \
 	-cdrom bin/kernel.iso &
 
-gdb \
+sleep 1
+
+kitty --class lappis-gdb -e gdb \
 	--quiet \
 	-command=debug.gdb
 
 ps ax | grep kitty | grep lappis-serial-log | awk '{print $1}' | xargs kill
 ps ax | grep kitty | grep lappis-serial-raw | awk '{print $1}' | xargs kill
-ps ax | grep qemu-system-x86_64 | grep kernel\.iso | awk '{print $1}' | xargs kill
+ps ax | grep kitty | grep lappis-qemu       | awk '{print $1}' | xargs kill

notes/logbook.md

@@ -11,3 +11,9 @@ Glitch art a la 1.44 MB style.
 *earlyclobber get's the clobb*
 
 Fix interrupt clobbering registers _semi-deterministically_.
+
+# 2022-05-26
+
+*Shellcoding on rollerblades like your in an 80is Hackers movie*
+
+A bug in `ld` caused the NX bit of page table entries to be discarded.

run.sh

@@ -13,11 +13,10 @@ qemu-system-x86_64 \
 	-no-reboot \
 	-no-shutdown \
 	-d int \
-	-m size=128M \
+	-m size=4G \
 	-serial file:/tmp/serial.log \
 	-serial file:/tmp/serial.raw \
 	-drive media=disk,index=0,file=bin/zipfs.img,format=raw,if=ide \
-	-drive media=disk,index=1,file=bin/fat32.img,format=raw,if=ide \
 	-monitor stdio \
 	-cdrom bin/kernel.iso