I am experiencing difficulty when attempting to use the C library function strcpy within an external NASM function designed to create a linked list of items. The function is designed to malloc nodes until a specific number of nodes is reached and control returns to the calling function. The node itself contains a nested structure which is also malloc()ed and contains two string/arrays of chars.
The strange thing is that the first invokation of strcpy works just as it should but the second instance, which has exactly the same except for the fact that it copies a different string to a different data member in the structure, I receive an "error: invalid operand type" error even though the syntax appears exactly the same. Does anyone have any suggestions
** I tried to only post the code that seemed necessary but will post more if required. I think this should suffice since the linked list functionality works fine and the name and address strings do take in information from the keyboard correctly. Its just copying the one addressString to the malloced struct.
The strange thing is that the first invokation of strcpy works just as it should but the second instance, which has exactly the same except for the fact that it copies a different string to a different data member in the structure, I receive an "error: invalid operand type" error even though the syntax appears exactly the same. Does anyone have any suggestions
** I tried to only post the code that seemed necessary but will post more if required. I think this should suffice since the linked list functionality works fine and the name and address strings do take in information from the keyboard correctly. Its just copying the one addressString to the malloced struct.
section .bss
nameString RESB 80
addressString RESB 80
STRUC linkedList
prev: RESD 1
next: RESD 1
m_empNode: RESD 1
ENDSTRUC ; end of struc
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
STRUC employee
m_empName: RESB 80
m_empAddress: RESB 80
ENDSTRUC ; end of struc
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; break into code after initialization of list and retrieving input data
; restore ECX register pointing to malloced EmployeeNode
POP ECX ; ECX =
; restore EBX register pointing to malloced ListNode
POP EBX
; if the headNode points to a null value, perform insert at the head
CMP dword , NULL
; otherwise, jump to insert at tail process
JNE insertTail
insertHead:
; copy name string to stuNode
PUSH dword nameString
PUSH dword ECX + m_empName
CALL strcpy
ADD ESP, 8
POP EDX
;; copy address string to employee node
PUSH dword addressString
PUSH dword EDX + m_empAddress <-----;;;;; THIS INSTRUCTION PRODUCES error: invalid operand type
CALL strcpy ;;;;; even though strcpy above it has a similar line and works fine
ADD ESP, 8
; put address of new node as headNode
MOV dword , EBX
; insert is complete
JMP insertComplete
insertTail:
MOV EDX, ECX
PUSH EDX
PUSH dword nameString
PUSH dword ECX + m_empName
CALL strcpy
ADD ESP, 8
POP EDX
PUSH dword addressString
PUSH dword EDX + m_empAddress<-----;;;;; THIS INSTRUCTION PRODUCES error: invalid operand type
CALL strcpy ;;;;; even though strcpy above it has a similar line and works fine
ADD ESP, 8
[\CODE]
Hm, I find it weird that NASM allows "PUSH dword ECX + m_empName" - that's not a valid x86 adressing mode. If you add square brackets to indicate a memory reference, then it's valid enough, but not what you want.
What you'll want is probably something like "lea eax, " along with a "push eax". Also remember that any external function call is free to trash EAX,ECX,EDX so you should either preserve those across external calls, or (usually smarter) used EBX,ESI,EDI,EBP instead.
Same goes for code of your own, if you're writing a callback: you're free to trash EAX,ECX,EDX but you must preserve the other four registers.
What you'll want is probably something like "lea eax, " along with a "push eax". Also remember that any external function call is free to trash EAX,ECX,EDX so you should either preserve those across external calls, or (usually smarter) used EBX,ESI,EDI,EBP instead.
Same goes for code of your own, if you're writing a callback: you're free to trash EAX,ECX,EDX but you must preserve the other four registers.
f0dder:
Thank you very much for your assistance and sorry for any inconvenience. Your suggestion seems to have fixed the problem.
Thank you very much for your assistance and sorry for any inconvenience. Your suggestion seems to have fixed the problem.
Don't say sorry - we're here to help. Glad to have been of assistance :)
PUSH dword ECX + m_empNamewhat does this assemble to? push ?