A patched TLS load calls TlsRegStub and SafeCall, which moved RSP past the
red zone with sub/add rsp,0x80. ADD and SUB write the arithmetic flags, so
the sub ran before SafeCall's pushfq saved them and the add ran after its
popfq restored them: guest code that compares, loads fs:[0] and then
branches on the flags could branch the wrong way. lea moves RSP without
touching the flags. The entry lea plus a two-byte nop keeps every patched
offset in both stubs; the exit lea is one byte longer and moves only ret.
TlsStubsPreserveFlags calls the stubs with two flag patterns and checks
the status flags, the output register and RAX; it fails with the old
bytes.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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