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