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In that case the application >> may not be able to use slice extension feature unless Libc’s use of rseq is disabled. > > In this case, wouldn't GLIBC's rseq registration fail if presumed > __rseq_size is smaller than the "struct rseq" size? The registered rseq size cannot be smaller than 32 bytes, else registration is refused by the system call (-EINVAL). The new slice extension fields would fit within those 32 bytes, so it should always work. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com