## writeup

└─$ wget https://artifacts.picoctf.net/c/509/disassembler-dump0_a.txt
--2023-07-30 22:08:23--  https://artifacts.picoctf.net/c/509/disassembler-dump0_a.txt
Resolving artifacts.picoctf.net (artifacts.picoctf.net)... 13.35.7.96, 13.35.7.31, 13.35.7.121, ...
Connecting to artifacts.picoctf.net (artifacts.picoctf.net)|13.35.7.96|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 209 [application/octet-stream]
Saving to: ‘disassembler-dump0_a.txt’

disassembler-dump 100%[===========>]     209  --.-KB/s    in 0s      

2023-07-30 22:08:27 (157 MB/s) - ‘disassembler-dump0_a.txt’ saved [209/209]

                                                                      
┌──(kali㉿kali)-[~/code]
└─$ cat disassembler-dump0_a.txt
<+0>:     endbr64 
<+4>:     push   rbp
<+5>:     mov    rbp,rsp
<+8>:     mov    DWORD PTR [rbp-0x4],edi
<+11>:    mov    QWORD PTR [rbp-0x10],rsi
<+15>:    mov    eax,0x30
<+20>:    pop    rbp
<+21>:    ret
                                                                      
┌──(kali㉿kali)-[~/code]
└─$ cat disassembler-dump0_a.txt | grep "eax"
<+15>:    mov    eax,0x30
                                                                      
┌──(kali㉿kali)-[~/code]
└─$ python3
Python 3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print(int("0x30",16))
48

=> picoCTF{48}
## what is eax
eax, ebx, ecx, edx, esi, edi, ebp, esp等都是**X86 組合語言中CPU上的通用寄存器**的名稱，是32位的寄存器。如果用C語言來解釋，可以把這些寄存器當作變數看待。

**比方說：add eax,-2 ; //可以認為是給變數eax加上-2這樣的一個值。**

這些32位寄存器有多種用途，但每一個都有“專長”，有各自的特別之處。

**EAX 是"累加器"(accumulator), 它是很多加法乘法指令的預設寄存器。**

source:
- https://topic.alibabacloud.com/tc/a/in-assembly-languages-eax-ebx-ecx-edx-esi-edi-ebp-and-esp_8_8_32031109.html
- https://ithelp.ithome.com.tw/m/articles/10227112
- https://primer.picoctf.com/#_assembly