Skip to content

Commit

Permalink
[boot] Add enhanced debug display to setup.S for early startup debugging
Browse files Browse the repository at this point in the history
  • Loading branch information
@ghaerr
ghaerr committed Sep 2, 2024
1 parent 33a7c93 commit 7b778cf
Showing 1 changed file with 156 additions and 27 deletions.
183 changes: 156 additions & 27 deletions elks/arch/i86/boot/setup.S
View file
Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,10 @@
#include <linuxmt/boot.h>

// Relocating loader debug option
#define DEBUG_LOADER 0
debug_output = 0 // display various register values during execution
serial_output = 0 // use INT 14 serial instead of INT 10 console out
debug_loader = 0 // display relocations


// Signature words to ensure LILO loaded us right
#define SIG1 0xAA55
Expand All @@ -103,6 +106,27 @@
.arch i8086, nojumps
.code16
.text
.section .text
.section .text.const
.section .text

.macro .hex4sp reg,msg
.if debug_output
push %ax
.ifnb \msg
.section .text.const
1: .ascii "\msg","\0"
.section .text
push %ax // in case reg is AX
mov $1b,%ax
call csputs
pop %ax
.endif
mov \reg,%ax
call hex4sp
pop %ax
.endif
.endm

.global _start
_start:
Expand All @@ -128,7 +152,16 @@ _start:
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// Entry point for kernels loaded from DISK

.hex4sp %ss,"\nSETUP boot SS:"
.hex4sp %sp,"SP:"
.hex4sp $INITSEG,"\nDEF_INITSEG:"
.hex4sp $REL_INITSEG,"-> REL_INITSEG:"
.hex4sp $SETUPSEG,"DEF_SETUPSEG:"
.hex4sp $SYSSEG,"\nDEF_SYSSEG: "
.hex4sp $REL_SYSSEG,"-> REL_SYSSEG: "

// Check signature at end of setup
cli
mov $SETUPSEG,%ax // DS = setup CS
mov %ax,%ds
cmpw $SIG1,setup_sig1
Expand All @@ -141,8 +174,7 @@ no_sig: lea no_sig_mess,%si
1: // And halt
jmp 1b

no_sig_mess: .ascii "No ELKS setup signature found ..."
.byte 0x00
no_sig_mess: .ascii "No ELKS setup signature found ...\0"

// If setup and kernel were loaded as a blob, we need to separate them out,
// then move to our own stack
Expand All @@ -156,17 +188,21 @@ chk_blob:
// lower address to a higher one
mov setup_sects,%al // find start of a.out kernel
xor %ah,%ah
.hex4sp %ax,"\nSetup sectors "
mov $5,%cl
shl %cl,%ax
add $SETUPSEG,%ax
mov syssize,%bp
.hex4sp %bp,"System paras "
.hex4sp %ax,"a.out seg "

mov %bp,%cx // first move the last sub-64KiB piece in place
and $0x0fff,%cx
xor %cx,%bp
xor %cx,%bp // and $0xf000,%bp
mov %ax,%dx
add %bp,%dx
mov %dx,%ds
lea SYSSEG(%bp),%dx
lea SYSSEG(%bp),%dx // move %bp,dx; add $SYSSEG,%dx
mov %dx,%es
jcxz move_kernel_in_64ks
shl %cx
Expand All @@ -176,6 +212,12 @@ chk_blob:
dec %si
shl %si
mov %si,%di
.hex4sp %ds,"\nCopy a.out to DEF_SYSSEG (last) DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"
.hex4sp %cx,"CX:"

rep
movsw
move_kernel_in_64ks:
Expand All @@ -190,6 +232,11 @@ move_kernel_in_64ks:
mov $0x80,%ch
mov $0xfffe,%si
mov %si,%di
.hex4sp %ds,"\nCopy a.out to DEF_SYSSEG (64K) DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"

rep
movsw
jmp move_kernel_in_64ks
Expand All @@ -198,7 +245,10 @@ done_move_kernel:
cld
mov $INITSEG,%ax
mov %ax,%ss
mov $0x4000-12,%sp
//mov $0x4000-12,%sp
mov $0x1000,%sp // 2K stack: 0x0800 setup size + 0x0800 stack
.hex4sp %ss,"\nNew INIT SS:"
.hex4sp %sp,"SP:"

no_blob:
#endif
Expand Down Expand Up @@ -268,13 +318,9 @@ err_loop:


msg_aout_err:
.byte 13,10
.ascii "ERROR: Wrong kernel a.out format"
.byte 0
.ascii "\r\nERROR: Wrong kernel a.out format\0"
msg_too_big:
.byte 13,10
.ascii "ERROR: kernel size > 64k"
.byte 0
.ascii "\r\nERROR: kernel size > 64k\0"

aout_ok:
mov 10,%cx // 10 = hiword hdr.a_text size
Expand Down Expand Up @@ -358,10 +404,15 @@ size_error:
mov $8,%cl // to words
shl %cl,%ax
mov %ax,%cx

mov $512,%si // skip raw sector
xor %di,%di
cld
.hex4sp %ds,"\nCopy DEF_SETUPSEG code to high mem DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"
.hex4sp %cx,"CX:"

rep
movsw

Expand All @@ -370,6 +421,8 @@ size_error:
mov %es,%ax
mov %ax,%ss // automatic CLI for next instruction
xor %sp,%sp
.hex4sp %ss,"\nNew HMEM SS:"
.hex4sp %sp,"SP:"

push %ax
mov $_next1,%ax
Expand All @@ -388,6 +441,12 @@ _next1:
xor %di,%di
mov $256,%cx
cld
.hex4sp %ds,"\nCopy DEF_INITSEG data to REL_INITSEG DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"
.hex4sp %cx,"CX:"

rep
movsw

Expand All @@ -414,8 +473,7 @@ sys_hdr_bad:
1: // halt
jmp 1b
sys_hdr_msg:
.ascii "Bad system header!"
.byte 0
.ascii "Bad system header!\0"

// System header is good

Expand Down Expand Up @@ -456,12 +514,20 @@ sys_hdr_good:
mov $REL_SYSSEG,%ax
mov %ax,%es
mov %ax,-18(%bp) // save .text segment
.ifeq debug_output
call hex4sp
.endif
add %dx,%ax // add code paragraphs
mov %ax,-20(%bp) // save .data start in case no .fartext
xor %di,%di

mov -2(%bp),%cx // code size in bytes
.hex4sp %ds,"\nCopy DEF_SYSSEG .text to REL_SYSSEG DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"
.hex4sp %cx,"CX:"

cld
rep
movsb
Expand Down Expand Up @@ -498,7 +564,15 @@ sys_hdr_good:
mov %ax,%es
mov %ax,-20(%bp) // save .fartext segment
xor %di,%di

.ifeq debug_output
call hex4sp
.endif
.hex4sp %ds,"\nCopy DEF_SYSSEG .ftext to REL_SYSSEG DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"
.hex4sp %cx,"CX:"

rep
movsb
Expand Down Expand Up @@ -530,9 +604,17 @@ sys_no_far_text:
mov %ax,%es
mov %ax,-22(%bp) // save .data segment
xor %di,%di
mov -4(%bp),%cx // data size

.ifeq debug_output
call hex4sp
.endif
.hex4sp %ds,"\nCopy DEF_SYSSEG .data to REL_SYSSEG DS:"
.hex4sp %si,"SI:"
.hex4sp %es,"ES:"
.hex4sp %di,"DI:"
.hex4sp %cx,"CX:"

mov -4(%bp),%cx // data size
rep
movsb

Expand Down Expand Up @@ -605,7 +687,22 @@ data_reloc:
mov -18(%bp),%ax // kernel .text segment
push %ax
push %cx
lret

.hex4sp %ss,"Done SS:"
.hex4sp %ds,"DS/ES:"
.hex4sp %bx,".text size:"
.hex4sp %di,".fartext size:"
.hex4sp %si,".data size:"
.hex4sp %ax,"\nJump CS:"
.hex4sp %cx,"entry:"
.if debug_output
.ifeq serial_output // if not serial output
xor %ah,%ah // read key press
int $0x16
.endif
.endif

lret // jump to REL_SYSSEG:_start to start kernel

// Relocate segment at ES: from relocation record at DS:SI
relocat:
Expand All @@ -631,7 +728,9 @@ relocat:

mov -22(%bp),%ax // kernel .data segment
3:
#if DEBUG_LOADER
mov %ax,%es:(%di)

.if debug_loader
push %ax // display [seg:off=val]
mov $'[',%ax
call putc
Expand All @@ -649,8 +748,8 @@ relocat:
mov $']',%ax
call putc
pop %ax
#endif
mov %ax,%es:(%di)
.endif

ret
9:
jmp sys_hdr_bad
Expand Down Expand Up @@ -679,6 +778,29 @@ puts: lodsb
jnz 1b
ret

.if debug_output
// Write AL to console, convert LF -> CR LF
putcc: cmp $'\n',%al
jnz 1f
push %ax
mov $'\r',%al
call putc
pop %ax
1: jmp putc

// Write CS:AX asciiz string to console
csputs: push %bx
mov %ax,%bx
1: mov %cs:(%bx),%al
test %al,%al
jz 2f
call putcc
inc %bx
jmp 1b
2: pop %bx
ret
.endif

// Output hex nibble, byte and word. All registers saved.
hex1: push %ax
and $0x0F,%al
Expand Down Expand Up @@ -721,8 +843,7 @@ hex4sp: call hex4
ret

hello_mess:
.ascii "\r\nELKS Setup "
.byte 0
.ascii "\r\nELKS Setup \0"

//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// Architecture specific routines for IBM PC
Expand Down Expand Up @@ -794,18 +915,26 @@ novga: mov %al,14 // CGA 25 rows
#endif
ret

// Write AL to console, save all other registers
putc: push %bx
// Write AL to console, save all registers
putc: push %ax
push %bx
push %cx
push %dx
push %bp // some BIOS may destroy BP
push %bp // some BIOS may destroy BP
.if serial_output
mov $1,%ah
xor %dx,%dx // COM1
int $0x14 // serial out
.else
mov $0x0E,%ah
mov $7,%bx // page 0
int $0x10
mov $7,%bx // page 0
int $0x10 // console out
.endif
pop %bp
pop %dx
pop %cx
pop %bx
pop %ax
ret

// include code to determine early CPU types
Expand Down

0 comments on commit 7b778cf

Please sign in to comment.