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fix 2F.4A MS-DOS v5 style HMA access services

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* Reject allocation call with too large requested size,
rather than allocating the remaining HMA.
* Align returned offset to paragraph boundary.
* Allow to allocate up to the very last byte of the HMA,
rather than 1 byte less.
* Pass last allocated byte to AllocateHMASpace instead
of the byte past it, which would carry for a full allocation.
This commit is contained in:
E. C. Masloch 2025-02-18 21:08:40 +01:00 committed by Kenneth J Davis
parent 5de2eb1aa0
commit 85be764a50
2 changed files with 26 additions and 12 deletions
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2
kernel/blockio.c
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@ -500,7 +500,7 @@ void AllocateHMASpace (size_t lowbuffer, size_t highbuffer)
do
{
/* check if buffer intersects with requested area */
if (FP_OFF(bp) < highbuffer && FP_OFF(bp+1) > lowbuffer)
if (FP_OFF(bp) <= highbuffer && FP_OFF(bp+1) > lowbuffer)
{
flush1(bp);
/* unlink bp from buffer chain */

36
kernel/inthndlr.c
View File

@ -1928,26 +1928,40 @@ VOID ASMCFUNC int2F_12_handler(struct int2f12regs FAR *pr)
{
COUNT rc;
long lrc;
UDWORD tsize;
UWORD requestedsize;
#define r (*pr)
if (r.AH == 0x4a)
{
size_t size = 0, offs = 0xffff;
size_t size = 0, offs = 0xffff, realoffs; /* defaults for no alloc */
r.ES = offs;
if (FP_SEG(firstAvailableBuf) == offs) /* HMA present? */
{
offs = FP_OFF(firstAvailableBuf);
size = ~offs; /* BX for query HMA */
if (r.AL == 0x02) /* allocate HMA space */
{
tsize = (r.BX + 0xf) & 0xfffffff0UL; /* align to paragraph */
if (tsize < size)
size = (UWORD)tsize;
AllocateHMASpace(offs, offs+size);
firstAvailableBuf += size;
realoffs = FP_OFF(firstAvailableBuf);
if (realoffs <= 0xFFF0) { /* if any free (not yet exthausted) */
offs = realoffs;
offs += 15;
offs &= ~ 15; /* annoying: buffers may be unaligned */
size = - offs; /* bx + di = 10000h */
if (r.AL == 0x02) /* allocate HMA space */
{
requestedsize = (r.BX + 15) & ~ 15; /* align to paragraph */
if (requestedsize < r.BX ||
requestedsize > size) { /* overflow or OOM */
size = 0;
offs = 0xffff; /* requested more than we have */
} else {
size = (UWORD)requestedsize; /* return rounded size */
AllocateHMASpace(realoffs, offs + size - 1); /* ! realoffs */
if ( ((UDWORD)offs + (UDWORD)size) == 0x10000UL ) {
firstAvailableBuf = MK_FP(0xFFFF, 0xFFFF); /* exhausted */
} else {
firstAvailableBuf += size; /* advance free pointer */
}
}
}
}
}
r.DI = offs;