[Phase 2.2/2.3] SYSCALL/SYSRET MSR setup + syscall dispatcher

syscall/mod.rs:
- Configure STAR (kernel CS=0x08, user base=0x10), LSTAR, SFMASK (clear IF),
  EFER.SCE to enable the SYSCALL/SYSRET instruction pair
- Naked assembly entry stub: swapgs, save/restore user RSP via per-CPU static,
  remap r10→rcx for Linux arg4 convention, call Rust syscall_handler, sysretq
- validate_user_ptr(): bounds check for all user pointers (0..USER_ADDR_MAX)
- set_syscall_kernel_stack(): for scheduler to update per-CPU kernel RSP

syscall/dispatch.rs:
- dispatch(): routes syscall numbers; unknown → -ENOSYS (never panics)
- sys_write(fd, buf, count): fd 1/2 → serial; validates user ptr; read_volatile
  loop avoids Rust aliasing assumptions on untrusted memory
- sys_exit(): serial log + hlt_loop() placeholder; Phase 2.5 adds scheduling

lib.rs: register syscall::init() + syscall::init_kernel_stack() in strix_os::init()

All existing integration tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions