initial jump

[lek_70]

oops! actually i wanna to know the destination of the initial jump of a com file... how to make it huh?

[CornedBee]

Assuming you read the binary file (without running a disassembler)
Here are the possible jump instructions:

EB  cb    JMP rel8        7+m             Jump short
E9  cw    JMP rel16       7+m             Jump near, displacement relative to next instruction
FF  /4    JMP r/m16       7+m/10+m        Jump near indirect
EA  cd    JMP ptr16:16    12+m,pm=27+m    Jump intersegment, 4-byte immediate address
EA  cd    JMP ptr16:16    pm=45+m         Jump to call gate, same  privilege
EA  cd    JMP ptr16:16    ts              Jump via task state segment
EA  cd    JMP ptr16:16    ts              Jump via task gate
FF  /5    JMP m16:16      43+m,pm=31+m    Jump r/m16:16 indirect and intersegment
FF  /5    JMP m16:16      pm=49+m         Jump to call gate, same  privilege
FF  /5    JMP m16:16      5 + ts          Jump via task state segment
FF  /5    JMP m16:16      5 + ts          Jump via task gate
E9  cd    JMP rel32       7+m             Jump near, displacement relative to next instruction
FF  /4    JMP r/m32       7+m,10+m        Jump near, indirect
EA  cp    JMP ptr16:32    12+m,pm=27+m    Jump intersegment, 6-byte immediate address
EA  cp    JMP ptr16:32    pm=45+m         Jump to call gate, same privilege
EA  cp    JMP ptr16:32    ts              Jump via task state segment
EA  cp    JMP ptr16:32    ts              Jump via task gate
FF  /5    JMP m16:32      43+m,pm=31+m    Jump intersegment, address at r/m dword
FF  /5    JMP m16:32      pm=49+m         Jump to call gate, same privilege
FF  /5    JMP m16:32      5 + ts          Jump via task state segment
FF  /5    JMP m16:32      5 + ts          Jump via task gate

Here's the operation format:


For more information, go here: http://webster.cs.ucr.edu/Page_TechDocs/Doc386/TOC.HTM