I am learning assembly development on Windows 10 (64-bit) and using IntelliJ IDEA to write my assembly code. I’m trying to log multiple outputs using WriteConsoleA, but only the first log message appears. The second log message is ignored.

First I tried to implement arithmetic logic to get the sum of two numbers. It didn’t work and I tried to hardcode the value and get a log result and then I realized this problem.

Here is my detailed setup and the code I am using.

Environment:

• Operating System: Windows 10 (64-bit)
• Assembler: NASM
• Compiler/Linker: MinGW-Win64

Code:

section .data
    sum_msg db 'Sum: ', 0
    sum db '15', 0

section .bss
    num_bytes_written resq 1

section .text
    global _start

    extern GetStdHandle
    extern WriteConsoleA
    extern ExitProcess

_start:
    ; Get the handle for stdout
    mov ecx, -11           ; STD_OUTPUT_HANDLE
    call GetStdHandle

    ; Check if handle is valid
    cmp rax, -1
    je .exit

    ; Write the "Sum: " message to stdout
    mov rcx, rax           ; handle to stdout
    lea rdx, [rel sum_msg] ; pointer to message
    mov r8d, 5             ; message length
    lea r9, [rel num_bytes_written]  ; pointer to number of bytes written
    call WriteConsoleA

    ; Write the hardcoded sum to stdout
    mov rcx, rax           ; handle to stdout
    lea rdx, [rel sum]     ; pointer to sum string
    mov r8d, 2             ; sum string length (including null terminator)
    lea r9, [rel num_bytes_written]  ; pointer to number of bytes written
    call WriteConsoleA

    ; Infinite loop to prevent immediate exit
.loop:
    nop
    jmp .loop

.exit:
    ; Exit
    xor ecx, ecx           ; exit code 0
    call ExitProcess

Commands:
Assemble code:

nasm -f win64 sum.asm -o sum.obj

Link code:

gcc -nostdlib -o sum.exe sum.obj -lkernel32

Expected Output:
Sum: 15

Actual output:
Sum:

Attempts to Fix:

• Verified that the initial message (“Sum: “) logs correctly.
• Added a loop to ensure the program doesn’t exit immediately, confirming that the second log is ignored.
• Tried changing the length of the second message.
• Confirmed that the WriteConsoleA function is called, but it doesn’t print the second message.
• Tested with hardcoded values for the second log message.
• Tried to compile the program by re-ordering the WriteConsoleA (top: “15”, bottom: “Sum: “) and it logs the “15” result.

What exactly do I need to know

• Why is the second call to WriteConsoleA not logging the message?
• Is there a specific requirement or constraint for calling WriteConsoleA multiple times in a 64-bit Windows assembly program?

Any help or suggestions would be greatly appreciated.