Common Memory References

There are a number of points in memory to which it is common to refer, e.g., the address of the instruction at the top of the disassembly window. These references are made easier by using one of the following shortcuts (all of which can be used anywhere on the command line where an address is expected such as BD .CODE, or BD .DATA L4 W):

.EA Effective Address of the first (or only) operand to the instruction at the top of the disassembly window
.EA2 Effective Address of the second operand to the instruction at the top of the disassembly window
.GDT GDT base address (using selector zero)
.IDT IDT base address (using selector zero)
.LDT LDT base address (using selector zero)
.TSS TSS base address (using selector zero)
.CMAC Seg:Off of next C MAC entry -- equivalent to .DATA + 2 + FFFE & [.DATA
.CODE current code display address
.CSIP current cs:[e]ip
.DATA current data display address
.DMAC Seg:0 of first DOS MAC entry
.NMAC Seg:0 of next DOS MAC entry -- equivalent to ((S..DATA)+1+[.DATA+3):0
.LBRFR EIP of Last Branch From
.LBRTO EIP of Last Branch To
.LEXFR EIP of Exception From
.LEXTO EIP of Exception To
.MDB Base address of the current Module Database (Windows only)
.PMIxx Sel|Off of PM Interrupt xxh
.RMIxx Seg:Off of RM interrupt # xx
.TDB Base address of the current Task Database (Windows only)
.VM Sel|Off of current Windows VM structure
.VMIxx Seg:Off of VM interrupt # xx
.VMRET Return CS|EIP saved in .VMSTK at .VMSTK+50 (DPMI fn 0300) or .VMSTK+150 (emulated INT)
.VMSTK Sel|Off of stack saved in .VM
.XBDA Seg:Off of XBDA; same as ([40:0E):0
.XBDA2 Seg:Off of 2ndary XBDA; same as ((S..XBDA)+[.XBDA+B4):0

A common address to jump to is the (near or far) return address of a subroutine. This is made easier by using shortened forms of the commands one might use to extract these addresses. The various flavors of return addresses are (where LaSTK is the address of the current stack pointer -- SS:SP if VM, SS|SP if PM and the B-bit in SS is clear, and SS|ESP if PM and the B-bit in SS is set):

Keyword Grammar Equivalent Meaning
.RETND {LaSTK Near dword
.RETNS [LaSTK Near word
.RETFD :{LaSTK or |{LaSTK Far word:dword or word|dword (depending upon the VM bit in the current EFL)
.RETFS :[LaSTK or |[LaSTK Far word:word or word|word (depending upon the VM bit in the current EFL)
.RETN .RETND or .RETNS Depending upon the D-bit in CS
.RETF .RETFD or .RETFS Depending upon the D-bit in CS
.IRET .RETF in VM
.RETFD in PM
Also allows mode switch from PM to VM by checking VM bit in EFL above return address

As a common shortcut, .RETN and .RETF refer to one of the above forms depending upon the setting of the D-bit in the current CS (that is, whether we're running in a USE16 or USE32 segment). Moreover, .IRET can be used as a shorthand for .RETF with the added check on the VM bit in the EFL above the return address. If this bit is set, the return address is interpreted as a VM address even though the current mode is PM.

No magic is invoked to extract the return address if data has been pushed onto the stack below the return address, so be sure that LaSTK points to the actual return address.

Also note that the keystrokes A-F and A-N are defined as shortcuts for the commands G .RETF and G .RETN, respectively.

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