vietlq/linux-assembly

Fun with Assembly on x86-64 Linux

Assembly Programming for x86-64 Linux

Tutorials

• Basic NASM tutorial: https://cs.lmu.edu/~ray/notes/nasmtutorial/

Books

• Assembly Language Step-by-Step Third Edition by Jeff Duntemann: https://www.amazon.co.uk/Assembly-Language-Step-Step-Third/dp/0470497025/

Debugging

Using GDB

Bare-bone debugging

• Run gdb path_to_my_asm
• Run break _start as the first thing. Note that in C/C++ you use break main but actually ELF has _start as the entry point
• Type run and the breakpoint will be at _start
• To step through each instruction, run si intead of s like in C/C++
• Read: https://sourceware.org/gdb/onlinedocs/gdb/Registers.html
• Run layout src to show window with source code (C, C++)
• To show assembly of the next line:

# From https://stackoverflow.com/a/29953542/128028
set  disassemble-next-line on
show disassemble-next-line

Debugging with vibrant TUI

• Start debugging session with: gdb -tui path_to_my_asm
• Run break _start as usual
• Run layout asm before or after executing run
• Run layout reg after executing run
• To step through each instruction, run si intead of s like in C/C++
• For better UI, look at https://github.com/cyrus-and/gdb-dashboard

# From https://stackoverflow.com/a/55935724/128028
dashboard -layout source assembly registers stack

Advanced GDB debugging

• Read: http://web.cecs.pdx.edu/~jrb/cs201/lectures/handouts/gdbcomm.txt

For more info, read:

• http://dbp-consulting.com/tutorials/debugging/basicAsmDebuggingGDB.html
• https://www-users.cs.umn.edu/~kauffman/2021/gdb
• https://www-zeuthen.desy.de/unix/unixguide/infohtml/gdb/TUI-Commands.html
• https://ftp.gnu.org/old-gnu/Manuals/gdb/html%5Fchapter/gdb%5F19.html

Caveats

• Use syscall instead of legacy int 80H on x86-32: https://stackoverflow.com/questions/12806584/what-is-better-int-0x80-or-syscall
• Registers for syscall have changed in x86-64: https://blog.rchapman.org/posts/Linux%5FSystem%5FCall%5FTable%5Ffor%5Fx86%5F64/
• Use latest syscall references: https://filippo.io/linux-syscall-table/
• If you must use Assembly on 32-bit Linux, see eatsyscall example and https://stackoverflow.com/a/4253672/128028 to create emulated 32-bit binary