LinuxLL Book 10 Minimal Runtime No libc

Inside the book

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• Low-Level Programming on Linux (x86-64) : Minimal Runtime (No libc) Prepared by Ayman Alheraki simplifycpp.org November 2025 Contents Contents 2 Author’s Introduction 5 1 Program Startup State 10 1.1 Stack Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.1.1 The Canonical Stack Image at _start . . . . . . . . . . . . . . . . . 11 1.1.2 Extracting argc, argv, and envp in Pure Assembly . . . . . . . . . 11 1.1.3 Navigating the Environment and Auxiliary Vector . . . . . . . . . . 13 1.1.4 Stack Integrity and Alignment Discipline . . . . . . . . . . . . . . . 14 1.1.5 Why the Stack Layout Matters in a No-libc Environment . . . . . . 14 1.2 argc / argv / envp Retrieval . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.1 Recovering argc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.2 Locating argv[] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.3 Retrieving envp[] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.4 Passing Arguments to C . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.5 Calling main Without libc . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.6 Rationale in a Minimal Runtime . . . . . . . . . . . . . . . . . . . . 19 2 3 2 Writing _start 20 2.1 Register and Stack Preparation . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.1.1 The ABI Constraint at Entry . . . . . . . . . . . . . . . . . . . . . . . 20 2.1.2 Register Clearing and Predictable State . . . . . . . . . . . . . . . 21 2.1.3 Stabilizing Access to the Kernel-Provided Stack Block . . . .