The initial bootstrap init (started directly by the kernel via
usermode_bootstrap) had RSP = 0 from InterruptStack::init(), which
does NOT set RSP. This caused any push/call in the binary to fault
on address 0.
The Rust panic handler caught the resulting page fault and generated
ud2 — visible as 'Invalid opcode fault' at a low RIP before main()
ever runs. This was the root cause of the init crash.
Fix:
- Map 8 pages (32 KiB) of user stack just above the initfs image
- Set RSP to the top of the stack
- Add debug log showing the mapped region
The stack is intentionally small (32 KiB) — enough for Rust _start
to run but small enough to detect stack overflow immediately. Once
init calls fexec_impl to spawn the real init, the real init gets its
own full 8 MB stack via the redox-rt exec path.
vasilito
397c701d45