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/* This routine potentially increases the stack size at runtime based on
the _stklen variable. Only used by DPMI code.
Copyright (c) 1993 C. Sandmann
Environment: called by crt0.s (and gcrt0.s)
EAX, EBX, EBP, EDI, ESI disposable (cleared on return) */
.text
.globl __setstack
__setstack:
movl %esp,%eax
andl $0xc0000000,%eax /* clear all except upper bits */
jne ok_stack /* obviously not DPMI! */
movw %ss,%ax
lsll %eax,%ebx /* stack segment limit */
movl %esp,%eax /* current location */
subl %ebx,%eax /* Free stack */
cmpl %eax,__stklen
jb ok_stack
/* Not enough stack. Call sbrk() to get a new area. Copy current ESP + 20
to end of new area (3 args + our stack). Change ESP to new area. Set new
limit to start of new area using DPMI services. */
pushl __stklen
call _sbrk /* eax = got memory base */
popl %ebx /* remove _stklen */
cmpl $0xffffffff,%eax /* if eax = -1 failure */
je badstack
addl %eax,%ebx /* ebx now is end of new stack area */
andl $0xfffffff0,%ebx /* 16 byte alignment */
addl $0xfff,%eax /* make stack base page aligned */
andl $0xfffff000,%eax /* 4096 byte alignment */
/* Now copy old stack to new stack. We only need our part + 4 words, 3 for
the parameters to pass to main, one for our return EIP (4 extra safety) */
movl %esp, %esi /* Source is current stack */
subl $0x20, %ebx /* 8 longwords */
movl %ebx, %edi /* Destination is new stack */
movl $8,%ecx
rep
movsl
/* New stack in place. Change ESP to point to it. Assumes new stack is
higher in memory so we don't get caught by limit. Change limit using
DPMI services. */
movl %ebx,%esp /* Switch to new stack */
subl $1,%eax /* Low 12 bits all 1s */
pushl %eax /* Easiest way to move long to words */
popw %dx
popw %cx
movl $8,%eax /* DPMI function Set Segment Limit */
movw %ss,%bx /* Selector */
int $0x31 /* Do service */
xor %ecx,%ecx /* Clean up */
xor %edx,%edx /* Clean up */
ok_stack:
ret /* What we have is already bigger */
badstack:
movl $0x4c01,%eax
int $0x21
jmp badstack
.data
.globl __stklen
.comm __stklen,4
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