Reverese Engineering

Reverese Engineering: Understanding a C program [Part2]

Empty Main funciton
assembly code for empty main
integer assignment
assembly code for integer assignment
another variable
a char variable
  • initialize an integer variable with a value of 5.
  • Compare the value the stored value with 10.
  • if the value is not equal then jump to the else section.
  • else follow the if section.
assembly equivalent
  • <+8> : initiate a variable and store the value of 5.
  • <+15> : compare the value with 0xa (decimal equivalent is 10)
  • <+19> : jump if not equal to (jne); jump on line (main+38). (main is the entry point here so its value is +0)
  • <+21>-<+31> : print “welcome”
  • <+36> : jump to line +53
  • <+38>-<+48> : print “invalid value”
values passed to the print statements
  • 0x400673 → W
  • 0x400674 → e
  • 0x400675 → l
  • 0x400676 → c
  • 0x400677 → o
  • 0x400678 → m
  • 0x400679 → e
  • 0x40067a → new line char (\n)
  • take input using the scanf function
  • compare the value with 0xa
  • take a jump if not equal to
  • else follow the path

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Connecting the dots and rest is magic. https://ayedaemon.github.io/

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Rishabh Umrao

Rishabh Umrao

Connecting the dots and rest is magic. https://ayedaemon.github.io/

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