How the Linux User/Kernel ABI Really Works - Driving the Linux Kernel Down at the Metal

Explore the intricate details of the Linux User/Kernel Application Binary Interface (ABI) in this comprehensive conference talk from C++Now 2025. Delve deep into the low-level mechanisms that govern how C and C++ programs interact with the Linux operating system, moving beyond the typical C library abstraction to understand the actual system-level implementation. Learn how system calls are truly implemented through various mechanisms including int 0x80, syscall instruction, vdso, and vsyscall page, and discover how return codes are translated into errno values. Examine the real workings of signal handlers, including the surprising syscall restart mechanism, and understand how pthreads map onto underlying OS primitives. Gain insights into the finer details of ptrace, the fundamental mechanism underlying debugging tools like strace and gdb. Explore how the kernel handles different types of signals, various scheduling states including 'uninterruptible sleep', and learn to extract valuable information from the /proc pseudo filesystem. Understand the practical applications of this knowledge for debugging without source code, performing fine-grained profiling and optimization, and writing intercept libraries. Discover surprising interactions and edge cases that emerge when these various mechanisms combine, providing essential knowledge for systems programmers working at the intersection of user space and kernel space.