Document the role of PTRACE_O_TRACESYSGOOD option in connection with PTRACE_GET_SYSCALL_INFO. Came upon this after writing a test program using PTRACE_GET_SYSCALL_INFO. After failing to find what's wrong I posted a StackOverflow question which you can find right here: <https://stackoverflow.com/questions/72410182/ptrace-get-syscall-info-always-returns-info-op-as-ptrace-syscall-info-none> Nate Eldredge found out what happens by looking into the kernel's source code, here is a link to the relevant part <https://github.com/torvalds/linux/blob/8291eaafed36f575f23951f3ce18407f480e9ecf/kernel/ptrace.c#L1018> In the code it can be seen that in case of system call entry or exit stops, the union is filled if and only if the signal matches `SIGTRAP | 0x80`, a signal which is only sent if the PTRACE_O_TRACESYSGOOD option is set. You can read about that in the PTRACE_O_TRACESYSGOOD section of ptrace(2)'s manual. Complements: fc91449cb "ptrace.2: Document PTRACE_GET_SYSCALL_INFO" Cowritten-by: Dmitry V. Levin <ldv@strace.io> Signed-off-by: Dmitry V. Levin <ldv@strace.io> Signed-off-by: Fotios Valasiadis <fvalasiad@gmail.com> Acked-by: Nate Eldredge <nate@thatsmathematics.com> Cc: Elvira Khabirova <lineprinter0@gmail.com> Signed-off-by: Alejandro Colomar <alx@kernel.org>