> On most platforms you can get argc and argv[] through the right system calls
Not (reliably) on Linux or, as far as I know, on similar systems. argv, environ, and the aux vector come from a horrible data structure the kernel creates on the stack.
The kernel just copies the data to the program's stack in a contiguous manner. Obtaining pointers to them can seem somewhat magical if you're writing a nolibc program but I wouldn't call it horrible.
I implemented it for my programming language with some rather simple assembly code:
I’m saying you can’t reliably get the information from syscalls. The runtime (i.e. whatever implements the actual entry point declared in the ELF headers) can get it reliably, as can any other code to which the runtime gives an appropriate pointer.
You can’t assume that /proc is procfs if you’re writing a low level runtime library.
If you can find the top of the stack, you can read the contents with reasonable reliability. But the top of the stack is not at a fixed address, and if you are writing low enough level code (container manager, init, etc), poking around in /proc at startup is not a great idea.
If you’re wiring a real runtime library, none of this matters: the kernel passes a pointer in a register at startup.
Not (reliably) on Linux or, as far as I know, on similar systems. argv, environ, and the aux vector come from a horrible data structure the kernel creates on the stack.