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[pxeprefix] Search for the PXE entry points through all methods
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Search for the PXE entry points (via the !PXE or PXENV+ structures)
through all known combinations of search methods.  Furthermore, if we
find a PXENV+ structure, attempt to use it to find the !PXE structure
if at all possible.
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H. Peter Anvin authored and Michael Brown committed Feb 23, 2009
1 parent 4dd746a commit 6a3f5d6
Showing 1 changed file with 105 additions and 42 deletions.
147 changes: 105 additions & 42 deletions src/arch/i386/prefix/pxeprefix.S
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Expand Up @@ -31,18 +31,10 @@
pushl $STACK_MAGIC
movw %ss, %cs:pxe_ss
movl %esp, %cs:pxe_esp
movw %sp, %bp
movl (10*4+4*2+4)(%bp),%ebp /* !PXE address */

/* Set up %ds */
/* Set up segments */
movw %cs, %ax
movw %ax, %ds
/* Record PXENV+ and !PXE nominal addresses */
movw %es, pxenv_segment /* PXENV+ address */
movw %bx, pxenv_offset
movl %ebp, ppxe_segoff /* !PXE address */
/* Set up %es and %fs */
movw %ax, %es
movw $0x40, %ax /* BIOS data segment access */
movw %ax, %fs
/* Set up stack just below 0x7c00 */
Expand All @@ -60,16 +52,57 @@
.previous

/*****************************************************************************
* Verify PXENV+ structure and record parameters of interest
* Find us a usable !PXE or PXENV+ entry point
*****************************************************************************
*/
detect_pxenv:
/* Signature check */
les pxenv_segoff, %bx
cmpl $0x4e455850, %es:(%bx) /* 'PXEN' signature */
jne no_pxenv
cmpw $0x2b56, %es:4(%bx) /* 'V+' signature */
jne no_pxenv
detect_pxe:
/* Plan A: !PXE pointer from the stack */
lgsl pxe_esp, %ebp /* %gs:%bp -> original stack */
lesw %gs:52(%bp), %bx
call is_valid_ppxe
je have_ppxe

/* Plan B: PXENV+ pointer from initial ES:BX */
movw %gs:32(%bp),%bx
movw %gs:8(%bp),%es
call is_valid_pxenv
je have_pxenv

/* Plan C: PXENV+ structure via INT 1Ah */
movw $0x5650, %ax
int $0x1a
jc 1f
cmpw $0x564e, %ax
jne 1f
call is_valid_pxenv
je have_pxenv
1:
/* Plan D: scan base memory for !PXE */
call memory_scan_ppxe
je have_ppxe

/* Plan E: scan base memory for PXENV+ */
call memory_scan_pxenv
jne stack_not_found

have_pxenv:
movw %bx, pxenv_offset
movw %es, pxenv_segment

cmpw $0x201, %es:6(%bx) /* API version >= 2.01 */
jb 1f
cmpb $0x2c, %es:8(%bx) /* ... and structure long enough */
jb 2f

lesw %es:0x28(%bx), %bx /* Find !PXE from PXENV+ */
call is_valid_ppxe
je have_ppxe
2:
call memory_scan_ppxe /* We are *supposed* to have !PXE... */
je have_ppxe
1:
lesw pxenv_segoff, %bx /* Nope, we're stuck with PXENV+ */

/* Record entry point and UNDI segments */
pushl %es:0x0a(%bx) /* Entry point */
popl entry_segoff
Expand All @@ -79,36 +112,22 @@ detect_pxenv:
pushw %es:0x20(%bx) /* UNDI data segment */
pushw %es:0x22(%bx) /* UNDI data size */
popl undi_data_segoff

/* Print "PXENV+ at <address>" */
movw $10f, %si
call print_message
call print_segoff
movb $( ',' ), %al
call print_character
jmp 99f
jmp check_have_stack
.section ".prefix.data", "aw", @progbits
10: .asciz " PXENV+ at "
.previous

no_pxenv:
xorl %eax, %eax
movl %eax, pxenv_segoff

99:

/*****************************************************************************
* Verify !PXE structure and record parameters of interest
*****************************************************************************
*/
detect_ppxe:
/* Signature check */
les ppxe_segoff, %bx
cmpl $0x45585021, %es:(%bx) /* '!PXE' signature */
jne no_ppxe
/* Record structure address, entry point, and UNDI segments */
pushw %es
popw ppxe_segment
have_ppxe:
movw %bx, ppxe_offset
movw %es, ppxe_segment

pushl %es:0x10(%bx) /* Entry point */
popl entry_segoff
pushw %es:0x30(%bx) /* UNDI code segment */
Expand All @@ -123,17 +142,60 @@ detect_ppxe:
call print_segoff
movb $( ',' ), %al
call print_character
jmp 99f
jmp check_have_stack
.section ".prefix.data", "aw", @progbits
10: .asciz " !PXE at "
.previous

no_ppxe:
xorl %eax, %eax
movl %eax, ppxe_segoff
is_valid_ppxe:
cmpl $0x45585021, %es:(%bx)
jne 1f
movzbw %es:4(%bx), %cx
cmpw $0x58, %cx
jae is_valid_checksum
1:
ret

is_valid_pxenv:
cmpl $0x4e455850, %es:(%bx)
jne 1b
cmpw $0x2b56, %es:4(%bx)
jne 1b
movzbw %es:8(%bx), %cx
cmpw $0x28, %cx
jb 1b

is_valid_checksum:
pushw %ax
movw %bx, %si
xorw %ax, %ax
2:
es lodsb
addb %al, %ah
loopw 2b
popw %ax
ret

memory_scan_ppxe:
movw $is_valid_ppxe, %dx
jmp memory_scan_common

99:
memory_scan_pxenv:
movw $is_valid_pxenv, %dx

memory_scan_common:
movw %fs:(0x13), %ax
shlw $6, %ax
decw %ax
1: incw %ax
cmpw $( 0xa000 - 1 ), %ax
ja 2f
movw %ax, %es
xorw %bx, %bx
call *%dx
jne 1b
2: ret

/*****************************************************************************
* Sanity check: we must have an entry point
*****************************************************************************
Expand All @@ -144,6 +206,7 @@ check_have_stack:
testl %eax, %eax
jnz 99f
/* No entry point: print message and skip everything else */
stack_not_found:
movw $10f, %si
call print_message
jmp finished
Expand Down Expand Up @@ -529,8 +592,8 @@ print_pxe_error:
*/
.section ".prefix.data"

pxe_ss: .word 0
pxe_esp: .long 0
pxe_ss: .word 0

pxe_parameter_structure: .fill 20

Expand Down

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