CODEWITHSUNDEEP
assemblyx86att
Telanore
Telanore

Reputation: 75

AT&T assembler substring

Say I have a string "Hello to everyone" in register %edx, and I want to move "Hello to e" to %eax, is this possible? And how? (Address to the string is in 12(%ebp)).

Upvotes: 0

Views: 390

Answers (1)

TravorLZH
TravorLZH

Reputation: 302

"Hello to everyone" in register %edx

You don't actually "have" the string in a register. Instead, you have memory reference to it.

If you do not want to truncate the original string. You can do this

; Method #1: Copy the cut part of the string to a new address %edi
movl $10,%ecx   ; Store the length of cut string to %ecx
movl %edx,%esi  ; Copy the address of original string to %esi (Source Index)
rep movsb       ; This instruction copies %ecx bytes from %esi to %edi (Destination Index)
movb $0,(%edi)
movl %edi,%eax

Use method #2 if you only want to modify the current string

; Method #2: Cut the current string
movb $0,10(%edx) ; Put a null-terminator at the end of letter 'e'

Upvotes: 1

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