longjmp moves the Windows stack bounds onto the stack of the target jump buffer so that exceptions and stack probes keep working after a jump between guest stacks. siglongjmp restored the same registers without that step, so a jump from a context stack back to the thread stack left the thread bounds describing the stack it had left.
C symbols in Mach-O carry a leading underscore, and its assembler has no
.type or .size directives. APS5_ASM_SYMBOL names a symbol the way the
assembler of the host expects it, APS5_ASM_FUNCTION_END closes a function
(.size on ELF, nothing elsewhere), and APS5_ASM_FUNCTION defines a global
function on macOS.
The fiber stack switch, the signal mask helpers, getcontext and their tests
use them instead of writing the ELF spelling. The assembly they produce on
Linux and Windows is the same as before.
PSXS5, SwanStationPS5 and Nuvio stop at start-up on setcontext on main,
and EVO Player and ProsperoStore do on Windows. The three are imported
by the statically linked OpenSSL's ASYNC code.
The three use FreeBSD 11's amd64 ucontext_t (mcontext at 0x10, mc_len
800, uc_link at 0x330, 0x370 bytes), which the titles are built
against: EVO Player's ASYNC_is_capable captures into a 0x370-byte stack
buffer, and async_fibre_makecontext sets uc_link at 0x330 and uc_stack
at 0x338. getcontext saves every register at its call in assembly and
stores the context as FreeBSD's sys_getcontext does: rax and rdx as 0,
the carry flag clear, the FXSAVE image and the signal mask, and nothing
from uc_link on. setcontext checks mc_len and mc_flags as set_mcontext
does, installs the signal mask, masks MXCSR with the host's MXCSR_MASK
and returns through iretq, so every general register and the flags are
restored and nothing is written below the target stack pointer.
makecontext follows FreeBSD 11's amd64 libc.
Windows checks guard-page growth and exception unwinding against the
stack bounds in the TEB. setcontext and longjmp now set them to the
stack they switch to, which makecontext registers and pins writable as
libSceFiber does for fiber stacks. OpenSSL enters a context with
setcontext and then switches with _setjmp and _longjmp.
Dean