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Implement User-Space System Call Interceptor Using ptrace

hard2/8

Write Hello World Using Only Raw syscall() Instructions Implement Custom System Call in Linux Kernel

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Implementation

Implement system call interceptor using ptrace.

Requirements:

Use fork() to create tracer and tracee processes
Child calls ptrace(PTRACE_TRACEME) and execs a program
Parent uses PTRACE_SYSCALL to trace system calls
Use PTRACE_GETREGS to read registers at syscall entry
Print syscall number and arguments
Continue and get return value at syscall exit
Parse common syscalls (read, write, open, close)
Print in readable format (similar to strace)
Handle multiple syscalls in a loop
Handle process termination
Show syscall names, not just numbers

Why This Matters

ptrace is the exact syscall gdb, strace, and Docker's `--cap-add=SYS_PTRACE` debugging workflows are built on, and it's also how sandboxes like early gVisor and rr's record-and-replay debugger intercept every syscall a traced process makes. The orig_rax-versus-rax distinction you'll implement here (entry vs exit stop) is a real, easy-to-get-backwards detail that trips up first-time strace-clone authors.

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main.c

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