TrustedUser
2,147
edits
Difference between revisions of "HOWTO-Reverse Engineering"
→Using IDA Effectively: fix syntax highlighting
Dreammaster (talk | contribs) m (Add a link to a website with a free intro to RE ebook) |
(→Using IDA Effectively: fix syntax highlighting) |
||
| Line 56: | Line 56: | ||
=== Naming Methods === | === Naming Methods === | ||
Methods can be renamed using the general 'N' hotkey (as well as via the menus), and the 'Y' can be used to specify a C-like prototype for a method. This is particularly useful when some of the parameters for a method are passed using registers. By explicitly documenting what the method expects, it makes it easier to remember later on when you're reversing methods that call it. Standard methods where parameters are passed via the stack are easy, since IDA can automatically set up the function prototype for you. If a method does have parameters passed in registers, prototypes like the below can be used: | Methods can be renamed using the general 'N' hotkey (as well as via the menus), and the 'Y' can be used to specify a C-like prototype for a method. This is particularly useful when some of the parameters for a method are passed using registers. By explicitly documenting what the method expects, it makes it easier to remember later on when you're reversing methods that call it. Standard methods where parameters are passed via the stack are easy, since IDA can automatically set up the function prototype for you. If a method does have parameters passed in registers, prototypes like the below can be used: | ||
< | <source lang="c"> | ||
int __usercall sub_100FB<ax>(__int8 param1<al>, int param2<bx>) | int __usercall sub_100FB<ax>(__int8 param1<al>, int param2<bx>) | ||
</ | </source> | ||
In this case, the method takes an 8-bit parameter in the al register, and another 16-bit value in bx, then returns a result in ax | In this case, the method takes an 8-bit parameter in the al register, and another 16-bit value in bx, then returns a result in ax | ||
| Line 66: | Line 66: | ||
When dealing with data, you'll frequently see cases like | When dealing with data, you'll frequently see cases like | ||
< | <source lang="asm"> | ||
mov bx, 30h | mov bx, 30h | ||
mul bx | mul bx | ||
mov ax, [bx+2D00h] | mov ax, [bx+2D00h] | ||
</ | </source> | ||
In this case, an initial index in the ax register is multiplied by 30h (30 hexadecimal = 48 decimal). So from this we can determine that the given structure is 48 bytes in size, and can create a new structure accordingly. For smaller sized structures, you may want to create as many 2 byte word fields as needed to make up the correct size for the structure. For larger sizes, the easiest way is to simply declare an array of the needed structure size - 1, and follow it with a single byte field. You can then delete/undefine the array. The remaining byte will keep the structure at the correct size, and you can then later fill in the fields as you find references to them. | In this case, an initial index in the ax register is multiplied by 30h (30 hexadecimal = 48 decimal). So from this we can determine that the given structure is 48 bytes in size, and can create a new structure accordingly. For smaller sized structures, you may want to create as many 2 byte word fields as needed to make up the correct size for the structure. For larger sizes, the easiest way is to simply declare an array of the needed structure size - 1, and follow it with a single byte field. You can then delete/undefine the array. The remaining byte will keep the structure at the correct size, and you can then later fill in the fields as you find references to them. | ||