maps

Phase 4 enriches the existing /proc/[pid]/maps implementation with a synthetic vDSO entry and adds a contract test verifying format correctness.

What already existed

The maps file was implemented during M5 and already iterated VMAs with correct start-end addresses, rwxp permissions, and file offsets. Anonymous VMAs at index 0 and 1 were labeled [stack] and [heap] respectively, matching the internal Vm layout where vm_areas[0] is always the stack and vm_areas[1] is always the heap.

vDSO synthetic entry

The vDSO is mapped directly into the page table at VDSO_VADDR = 0x1000_0000_0000 during setup_userspace() without creating a VMA. This means it was invisible in /proc/[pid]/maps.

The fix adds a synthetic entry after the VMA loop:

100000000000-100000001000 r-xp 00000000 00:00 0          [vdso]

This is gated behind #[cfg(target_arch = "x86_64")] since ARM64 doesn't currently have a vDSO. Tools like ldd, glibc's dynamic linker, and GDB look for [vdso] when resolving clock_gettime.

Contract test

The new proc_maps.c test:

mmaps an anonymous page, then reads /proc/self/maps
Verifies [stack] annotation exists
Verifies [heap] annotation exists
Validates the XXXXXXXX-XXXXXXXX rwxp line format
Confirms the mmap'd address appears in the output

Results

23/23 contract tests pass (6/6 subsystem tests including the new proc_maps).

What's next

Phase 5 handles /proc/[pid]/fd/ directory and symlinks — the interface that ls -l /proc/self/fd/ and lsof use to enumerate open file descriptors.