// open input file im --IF JA zA IA im ##2. sy // open output file im --OF JA im ##241. IA im ##1ed. DA im ##2. sy // write ELF header im ##4. JA output fd im ##400000. address of ELF header in this executable IA im ##78. length DA im ##1. write sy // read next line ::rl im --LI RA rbp pointer to line buffer ::rL read loop im ##3. input file descriptor JA IR where to read into im ##1. DA read 1 byte im ##0. syscall 0 (read) sy // check how many bytes were read BA im ##1. jg if 1 greater than number of bytes read :-ef end of file BR DR pointer to character we just read im ##1. +B RA BD zA lb BA im ##a. jn :-rL keep looping // we now have a full line from the file in ::LI // the pointer to the end of the line is in rbp // look at the first character im --LI BA zA lb BA im ##3b. ascii ';' je if it's a comment, :-rl jump back to read the next line im ##a. ascii '\n' je if it's a blank line, :-rl jump back to read the next line im ##3a. ascii ':' je :-ld label definition jm :-ex // label definition ::ld // first, check if we're on the second pass. im --2P BA zA lb BA zA jn if on second pass, :-rl ignore this (read next line) // first get current address im ##4. output fd JA zA IA offset = 0 im ##1. whence = SEEK_CUR DA im ##8. syscall 8 = lseek sy BA im ##400000. address of start of file +B DA put current address in rdx im --L$ BA lq JA im --LI IA // copy from rsi to rdi until a newline is reached ::lc label copy BI zA lb BA // store in rdi AJ xc sb CA put byte in rcx // increment rdi,rsi BJ im ##1. +B JA BI im ##1. +B IA BC im ##a. jn if byte we read wasn't a newline, :-lc keep looping // store address of label in rdi AD BJ sd // increment rdi by 4, because we stored an 4-byte number im ##4. +B JA // now set L$ to rdi im --L$ BA AJ sq // read the next line jm :-rl // label lookup--set rax to address of label in rbx ::ll RB put ptr to label in rbp // if it's the first pass, just return 0 im --2P BA zA lb BA zA je :-r0 // okay it's not the second pass im ##a. CA terminator '\n' // use rsi to keep track of position in label list im --LB IA ::lL // first, check if we've reached the end of the label list (rsi == *L$) im --L$ BA lq BI je :-bl bad label if we've reached the end JR im --s= cl BA im ##1. je :-l= // this isn't the label; advance ::l\ zA BI lb DA // increment rsi BI im ##1. +B IA // check if that byte we looked at was a newline BD im ##a. jn :-l\ if not, keep looping // now we need to increment rsi by another 4 bytes, to skip over the address BI im ##4. +B IA jm :-lL re ::l= // label found! // first, increment rsi past newline: BI im ##1. +B IA // then, read dword at rsi into rax BI zA ld // we're done!! re // set rax to 1/0 depending on whether rsi and rdi have the same string, up to the terminator in rcx. ::s= BI zA lb DA BJ zA lb BD jn :-r0 1st characters are not equal BC je :-r1 we reached the end of the string // increment rsi, rdi BI im ##1. +B IA BJ im ##1. +B JA jm :-s= keep looping // return 0 ::r0 zA re // return 1 ::r1 im ##1. re // exit with code in rax ::ex JA im ##3c. sy // convert string representation of number starting at rbx and ending with a newline to number in rax ::nu DB im ##1. +B IA start by storing pointer to actual number (not including base) in rsi BD zA lb BA im ##64. ascii 'd' je :-#d decimal im ##78. ascii 'x' je :-#x hexadecimal jm :-bn unrecognized number base // convert newline-terminated decimal representation in rsi to number in rax ::#d zA JA use rdi to store number ::dL decimal loop BI zA lb BA im ##a. je :-d$ newline reached im ##30. jg :-bn bad digit (<'0') im ##39. jl :-bn bad digit (>'9') im ##ffffffffffffffd0. +B CA put numerical value of digit in rcx im ##a. BA AJ +* multiply by 10 BC +B add digit JA // increment rsi BI im ##1. +B IA jm :-dL keep looping ::d$ AJ re return ::#x zA JA use rdi to store number ::xL hexadecimal loop BI zA lb BA im ##a. je :-x$ newline reached im ##30. compare with ascii '0' jg :-bn bad if < '0' im ##39. jl :-af probably a-f im ##ffffffffffffffd0. -48 jm :-hX ::af im ##61. ASCII 'a' jg :-bn bad digit (not 0-9, and less than 'a') im ##66. ASCII 'f' jl :-bn bad digit (not 0-9, and greater than 'f') im ##ffffffffffffffa9. -87 (10 - 'a') ::hX +B BA // digit's numerical value now in rbx AJ