From: John Tsiombikas <nuclear@member.fsf.org>
Date: Tue, 24 Apr 2018 23:42:31 +0000 (+0300)
Subject: second stage boot loader now loads the main program
X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=commitdiff_plain;h=559dd7c3c836a69eac46bd12c7ef61bb5de8882c

second stage boot loader now loads the main program
---

diff --git a/Makefile b/Makefile
index 7fa61b9..0722ce4 100644
--- a/Makefile
+++ b/Makefile
@@ -20,12 +20,20 @@ ifneq ($(shell uname -m), i386)
 	ldarch = -m elf_i386
 endif
 
-floppy.img: $(bin)
+floppy.img: boot.img
 	dd if=/dev/zero of=$@ bs=512 count=2880
 	dd if=$< of=$@ conv=notrunc
 
+boot.img: bootldr.bin $(bin)
+	cat bootldr.bin $(bin) >$@
+
+# bootldr.bin will contain only .boot and .boot2
+bootldr.bin: $(elf)
+	objcopy -O binary -j '.boot*' $< $@
+
+# the main binary will contain every section *except* .boot and .boot2
 $(bin): $(elf)
-	objcopy -O binary $< $@
+	objcopy -O binary -R '.boot*' $< $@
 
 $(elf): $(obj)
 	$(LD) -o $@ $(obj) -Map link.map $(LDFLAGS)
@@ -37,12 +45,21 @@ $(elf): $(obj)
 
 .PHONY: clean
 clean:
-	rm -f $(obj) $(bin) floppy.img
+	rm -f $(obj) $(bin) boot.img floppy.img link.map
 
 .PHONY: cleandep
 cleandep:
 	rm -f $(dep)
 
+.PHONY: disasm
+disasm: bootldr.disasm $(elf).disasm
+
+bootldr.disasm: $(elf)
+	objdump -d $< -j .boot -j .boot2 -m i8086 >$@
+
+$(elf).disasm: $(elf)
+	objdump -d $< -j .startup -j .text -m i386 >$@
+
 .PHONY: run
 run: $(bin)
 	qemu-system-i386 -fda floppy.img -serial file:serial.log
diff --git a/pcboot.ld b/pcboot.ld
index 4879417..e2c0308 100644
--- a/pcboot.ld
+++ b/pcboot.ld
@@ -7,7 +7,11 @@ SECTIONS {
 	.boot : { * (.boot); }
 
 	/* second stage boot loader */
-	.boot2 : { * (.boot2); }
+	.boot2 : {
+		* (.boot2);
+		/* pad the boot loader to the next sector boundary */
+		. = ALIGN(512);
+	}
 	_boot2_size = SIZEOF(.boot2);
 
 	/* main program will be loaded at 1MB by the second stage
diff --git a/src/boot/boot.s b/src/boot/boot.s
index b976ec7..50817a3 100644
--- a/src/boot/boot.s
+++ b/src/boot/boot.s
@@ -15,7 +15,7 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 	.code16
-	.section .boot,"a"
+	.section .boot,"ax"
 
 	.set stack_top, 0x7be0
 	.set read_retries, 0x7be8
diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index 161bd73..6372557 100644
--- a/src/boot/boot2.s
+++ b/src/boot/boot2.s
@@ -16,7 +16,7 @@
 
 # this is the second-stage boot loader
 	.code16
-	.section .boot2,"a"
+	.section .boot2,"ax"
 
 	.set main_load_addr, 0x100000
 
@@ -230,15 +230,15 @@ ldloop:
 	mov $10, %ax
 	call putchar
 
-	# DBG
-	hlt
-
 	ret
 
 rdtrk_msg: .asciz "Reading track: "
 rdcyl_msg: .asciz " - cyl: "
 rdhead_msg: .asciz " head: "
 rdsect_msg: .asciz " start sect: "
+rdlast_msg: .asciz " ... "
+rdok_msg: .asciz "OK\n"
+rdfail_msg: .asciz "failed\n"
 
 read_retries: .short 0
 
@@ -292,8 +292,8 @@ read_try:
 	call putstr
 	mov trk_sect, %eax
 	call print_num
-	mov $10, %al
-	call putchar
+	mov $rdlast_msg, %esi
+	call putstr
 
 	# start sector (1-based) in cl[0, 5]
 	mov trk_sect, %al
@@ -320,11 +320,13 @@ read_try:
 	jmp read_try
 
 read_fail:
+	mov $rdfail_msg, %esi
+	call putstr
 	jmp abort_read
 
 read_ok:
-	mov $35, %ax
-	call putchar
+	mov $rdok_msg, %esi
+	call putstr
 
 	# reset es to 0 before returning
 	xor %ax, %ax
diff --git a/src/startup.s b/src/startup.s
index 42e4b21..bff3991 100644
--- a/src/startup.s
+++ b/src/startup.s
@@ -15,16 +15,19 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 	.code32
-	.section .startup
+	.section .startup,"ax"
 
 	.extern _bss_start
 	.extern _bss_end
 
+	# zero the BSS section
 	xor %eax, %eax
 	mov _bss_start, %edi
 	mov _bss_size, %ecx
+	jz skip_bss_zero
 	shr $4, %ecx
 	rep stosl
+skip_bss_zero:
 
 
 logohack:
@@ -131,8 +134,6 @@ xval: .long 0
 yval: .long 0
 frameno: .long 0
 
-numbuf: .space 16
-
 logo_pal:
 	.incbin "logo.pal"