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pbs: allow 9bootfat start cluster beyond 0xFFFF

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pbs failed to load (silently loading garbage) 9BOOTFAT from start
cluster beyond FFFF because we ignored the low word from the
directory entry. now taking the high 16 bit of the directory's
start cluster into account.
This commit is contained in:
cinap_lenrek 2013-05-06 01:15:46 +02:00
parent d3b727db18
commit cd66b11f67
2 changed files with 16 additions and 11 deletions
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26
sys/src/boot/pc/pbs.s
View file

@ -156,43 +156,47 @@ _nextdir:
_found:
CLR(rBX)
LW(_rootsize(SB), rAX) /* calculate and save Xrootsz */
LWI(0x20, rCX)
MUL(rCX)
LW(_sectsize(SB), rCX)
PUSHR(rCX)
DEC(rCX)
ADD(rCX, rAX)
ADC(rBX, rDX)
POPR(rCX) /* _sectsize(SB) */
INC(rCX)
DIV(rCX)
PUSHR(rAX) /* Xrootsz */
LXW(0x1a, xSI, rAX) /* starting sector address */
DEC(rAX) /* that's just the way it is */
DEC(rAX)
LB(_clustsize(SB), rCL)
CLRB(rCH)
CLR(rCX)
LXW(0x1a, xSI, rAX) /* start cluster low */
LXW(0x14, xSI, rBX) /* start cluster high */
SUBI(2, rAX) /* cluster -= 2 */
SBB(rCX, rBX)
LB(_clustsize(SB), rCL) /* convert to sectors (AX:DX) */
IMUL(rCX, rBX)
MUL(rCX)
ADD(rBX, rDX)
LW(_volid(SB), rCX) /* Xrootlo */
ADD(rCX, rAX)
LW(_volid+2(SB), rCX) /* Xroothi */
ADC(rCX, rDX)
CLR(rBX)
POPR(rCX) /* Xrootsz */
ADD(rCX, rAX)
ADC(rBX, rDX)
PUSHR(rAX) /* calculate how many sectors to read */
PUSHR(rAX) /* calculate how many sectors to read (CX) */
PUSHR(rDX)
LXW(0x1c, xSI, rAX)
LXW(0x1e, xSI, rDX)
LW(_sectsize(SB), rCX)
PUSHR(rCX)
DEC(rCX)
ADD(rCX, rAX)
ADC(rBX, rDX)
POPR(rCX) /* _sectsize(SB) */
INC(rCX)
DIV(rCX)
MW(rAX, rCX)
POPR(rBX)

1
sys/src/boot/pc/x16.h
View file

@ -117,6 +117,7 @@
BYTE $i;
#define SHRBI(i, r) OPrr(0xC0, 0x05, r); /* r>>i -> r */ \
BYTE $i;
#define SBB(r0, r1) OPrr(0x19, r0, r1) /* r1-r0 -> r1 */
#define SUB(r0, r1) OPrr(0x29, r0, r1) /* r1-r0 -> r1 */
#define SUBI(i, r) OP(0x81, 0x03, 0x05, r);/* r-i -> r */ \
WORD $i;