Under Rosetta the main thread stack lies at about 12 GiB, inside the guest
arena, where a title can map fixed addresses; a fixed mapping over it
aborts with a host region overlap.
- Aps5StartGuest moves the main thread onto a 16 MiB stack at
0x600000000000 when the old stack overlaps a host region of the arena.
It copies argv, environ, the program name and the initial block off the
old stack, then frees the old stack and releases its range to the arena.
- The guest thread keeps the stack size of the original main thread.
- The arena gets GuestArenaOverlapsHostRegion and
GuestArenaReleaseHostRegion for POSIX hosts.
- guest_main_stack_move starts the guest, then requires the main thread
outside the arena, a fixed mapping where the old stack was, and argv and
the environment intact.
Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
FreeBSD code reaches its thread pointer through %fs and macOS cannot set
the fs base. The macOS relinker turns each %fs access of a guest image
into a stub that reads the thread pointer from a pthread key and calls
Aps5GuestTlsAllocate on a thread's first access, registers the TLS
descriptor of an image with Aps5GuestTlsRegister, and routes
__tls_get_addr to Aps5GuestTlsGetAddr. No library provided them, so a
relinked executable could not start.
- Aps5GuestTlsRegister validates the descriptor the relinker wrote and
creates the key; its destructor frees the block of a thread.
- Aps5GuestTlsAllocateThreadPointer allocates the block (the TLS template
followed by zeros, then a 0x100-byte thread control block whose first
word points at itself, as on FreeBSD) and stores the thread pointer
under the key.
- Aps5GuestTlsAllocate is the entry the stubs call: rax holds the
descriptor and returns the thread pointer, every other register is
preserved, the upper halves of the ymm registers only where AVX exists.
- Aps5GuestTlsGetAddr returns the block of the thread plus the offset.
Co-authored-by: mugurc <[email protected]>
FreeBSD 11.4's sys___sysctl and userland_sysctl copy the name and the
old length in, and copy the value and the length out, so a bad pointer
gives EFAULT in that order. sysctl dereferenced them directly, and
sysctlbyname read its name with strcmp.
Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
- mlock on macOS wires only the pages libkernel has not wired yet. XNU
counts each wire of a page, and the locked ranges merge overlapping
locks, so a page locked twice stayed wired after munlock and
munlockall. The mlock test checks the wire count on macOS.
- mprotect changes a watched page through GuestWriteWatchProtect, which
applies the host protection and records it under the write watch's
lock, so a collection on another thread cannot run between the two.
The write watch test covers it.
- sceKernelVirtualQuery takes a watched page's write permission from the
write watch for memory outside the guest allocation registry.
- GuestAllocationsGuestPages counts an image segment up to the end of
its last host page, as the image page collection does.
- The macOS includes stay in main's include block, so the host code
other pull requests add there still sees them; the unused Mach-O
headers and the end trim, which never changed the protected spans,
are gone, and the guest page size is passed in.
- The libc and libkernel debt entries describe what is wired now.
- mprotect: the guest rounds a range to its 16 KiB pages. A Mach-O image
is loaded at a multiple of the host page size only (4 KiB under
Rosetta), so the pages are counted from where the ELF address 0 of the
image holding the range was loaded, and a rounded edge smaller than a
guest page that lies in the gap between two segments, where no host page
exists, is left out. The write watch is told the new protection.
- sceKernelVirtualQuery reads the region with mach_vm_region.
- sceKernelMunlockall unlocks the ranges libkernel locked, one by one:
macOS has no munlockall, which fails there with ENOSYS and would
overwrite errno.
- The stack protect test reads page protections with mach_vm_region.
This is mugurc's f66a4df741 from his macOS series, without the mlock
check that #10889 adds.
Co-authored-by: mugurc <[email protected]>
