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pbs: dont rely on chainloader to hand us a partition table and properly get the partition offset from nhidden in the fat header, add compare after mul because MUL doesnt set ZF but makes it undefined!

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cinap_lenrek 2011-06-13 05:34:19 +00:00
parent e3e5702780
commit cd5cef000f
1 changed files with 27 additions and 25 deletions
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52
sys/src/boot/pc/pbs.s
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@ -36,8 +36,10 @@ TEXT _nhiddenhi(SB), $0
TEXT _bigvolsize(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00;
/* FAT32 structure, starting @0x24 */
TEXT _fatsz32(SB), $0
BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
TEXT _fatsz32lo(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _fatsz32hi(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _extflags(SB), $0
BYTE $0x00; BYTE $0x00
TEXT _fsver(SB), $0
@ -76,14 +78,12 @@ _start0x5A:
MTSR(rAX, rES)
LWI(0x100, rCX)
MW(rSI,rBX) /* address of partition record -> rBX */
LWI(RELOC, rSI)
MW(rSI, rSP)
LWI(_magic(SB), rDI)
CLD
REP; MOVSL /* MOV DS:[(E)SI] -> ES:[(E)DI] */
PUSHA
MW(rSP, rBP)
PUSHR(rCX)
@ -96,39 +96,41 @@ _halt:
TEXT start16(SB), $0
STI
LWI(hello(SB), rSI)
CALL16(print16(SB))
PUSHR(rDX)
PUSHR(rBX)
PUSHR(rDX) /* drive */
LB(_nfats(SB), rCL) /* # of fats */
LW(_fatsize(SB), rAX) /* fat size */
MUL(rCX) /* DX:AX = #sectors */
JNE _fatszok /* zero? it's FAT32 */
CLR(rDX)
LW(_fatsize(SB), rAX)
CLR(rCX)
LB(_nfats(SB), rCL)
MUL(rCX)
OR(rCX, rCX)
JNE _fatszok /* zero? it's FAT32 */
LW(_fatsz32+2(SB), rBX) /* hi word */
IMUL(rCX, rBX) /* ... in sectors */
LW(_fatsz32(SB), rAX) /* lo word */
MUL(rCX) /* ... in sectors */
ADD(rBX, rDX) /* DX:AX = #sectors */
LW(_fatsz32hi(SB), rBX)
IMUL(rCX, rBX)
LW(_fatsz32lo(SB), rAX)
MUL(rCX)
ADD(rBX, rDX)
_fatszok:
POPR(rBX) /* address of partition record */
LXW(8, xBX, rCX) /* lo partition LBA */
LW(_nhiddenlo(SB), rCX)
ADD(rCX, rAX)
LXW(10, xBX, rCX) /* hi partition LBA */
LW(_nhiddenhi(SB), rCX)
ADC(rCX, rDX)
CLR(rBX)
LW(_nresrv(SB), rCX) /* # of reserved */
LW(_nresrv(SB), rCX)
ADD(rCX, rAX)
ADC(rDX, rBX)
SW(rAX, _volid(SB)) /* save for later use */
SW(rDX, _volid+2(SB))
POPR(rDX)
SW(rAX, _volid(SB)) /* save for later use */
SW(rBX, _volid+2(SB))
POPR(rDX) /* drive */
PUSHR(rBP)
LW(_sectsize(SB), rCX)
@ -164,7 +166,7 @@ _nextdir:
JMP _nextsect
_found:
PUSHR(rDX)
PUSHR(rDX) /* drive */
CLR(rBX)
@ -208,7 +210,7 @@ _found:
MW(rAX, rCX)
POPR(rBX)
POPR(rAX)
POPR(rDX)
POPR(rDX) /* drive */
LWI(RELOC, rSI)
PUSHR(rSI)