The behavior of PTRACE_SYSEMU on arm64 appears to differ substantially from that of x86 and powerpc (the other two architectures on which this feature is implemented). In particular, after PTRACE_SYSEMU the syscall will always be skipped on x86 and powerpc, but executed on arm64 unless the syscall-entry stop was again continued using PTRACE_SYSEMU. The skipping behavior is also documented in the manpage, so I suspect this may just be a bug (the skipping behavior makes sense to me and is what I would expect). The reason this happens is that `syscall_trace_enter` re-checks TIF_SYSCALL_EMU after the ptrace stop, but at that point it may have already been superseded by a new ptrace request. x86 and power save the original value of the flag, rather than acting on the new value. I can submit a patch to fix this, but wanted to check first whether this was intentional. If it is, I can fix the man page instead.
Keno
