What value gets stored in a3 when -S execve?

Hi Steve Grubb and Linux-Audit team, I'm Vish and I am a newbie to auditd. My requirement is to log only shell/bash commands and custom commands executed by administrator users. I have created these rules in /etc/audit/rules.d/audit.rules, to ensure SYSCALL, EXECVE are being added to audit.log for administrator users with auid greater than 1000: -a exit,always -F arch=b64 -S execve -F auid>=1000 -F auid!=-1 -k log_cmd -a exit,always -F arch=b32 -S execve -F auid>=1000 -F auid!=-1 -k log_cmd After restarting auditd service, I had executed strace on a simple command which will display version of my project's toolkit: ~# strace -e trace=execve toolkit-version-show execve("/var/tmp/toolkit-version-show", ["toolkit-version-show"], 0x7ffef1fa38b0 /* 30 vars */) = 0 Toolkit Version: 1.01 +++ exited with 0 +++ Later, I executed the ausearch command to check the log entry: ~# ausearch -i --start recent ---- type=EXECVE msg=audit(05/27/2020 19:01:26.605:12725) : argc=2 a0=/usr/bin/perl a1=/var/tmp/toolkit-version-show type=SYSCALL msg=audit(05/27/2020 19:01:26.605:12725) : arch=x86_64 syscall=execve success=yes exit=0 a0=0x7ffef1fa2450 a1=0x7ffef1fa38a0 a2=0x7ffef1fa38b0 a3=0x7f47f8669740 items=3 ppid=3641 pid=3643 auid=administrator uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=pts0 ses=8936 comm=toolkit-version-sho exe=/usr/bin/perl key=log_cmd ---- type=EXECVE msg=audit(05/27/2020 19:01:26.601:12724) : argc=4 a0=strace a1=-e a2=trace=execve a3=toolkit-version-show type=SYSCALL msg=audit(05/27/2020 19:01:26.601:12724) : arch=x86_64 syscall=execve success=yes exit=0 a0=0x55a2d44c9010 a1=0x55a2d449fe80 a2=0x55a2d4389490 a3=0x8 items=2 ppid=3099 pid=3641 auid=administrator uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=pts0 ses=8936 comm=strace exe=/usr/bin/strace key=log_cmd ---- My understanding of a0 - a2: Please refer the syntax of execve() : int execve(const char*filename, char *const argv[], char *const envp[]); Based on syntax of execve() and output from strace, I could understand that in audit.log event entry: a0=0x7ffef1fa2450 represents filename argument of execve a1=0x7ffef1fa38a0 represents argv[] argument of execve a2=0x7ffef1fa38b0 represents envp[] argument of execve Question 1: What does the a3=0x7f47f8669740 value represent? As execve() has only 3 arguments (represented by a0,a1,a2), what value gets stored in a3? I have noticed a3 values to be varying from: a3=0x0 a3=0x7 a3=0x55a2d4389490 a3=0x56a2d44adc00 a3=0x8 Question 2: a3=0x8 seems to be the value assigned for a majority of execve() syscalls. Is this a standard value set in case of main/primary system call, such as toolkit-version-show? Could I use this in a rule filter *-F a3=8* to log only primary (custom script) command executed by user and not internal commands executed by custom script like ls, cat, grep.. etc.: -a exit,always -F arch=b64 -S execve *-F a3=8* -F auid>=1000 -F auid!=-1 -k log_cmd -a exit,always -F arch=b32 -S execve *-F a3=8* -F auid>=1000 -F auid!=-1 -k log_cmd Would I miss logging a few primary syscalls, if a3 is not 0x80 in some cases? Question 3: If a3=0x8 is not a standard value, Is it possible to identify primary custom command and log only that command, and not internal commands with a3=0x0 or a3=0x55a2d4389490? Question 4: Is it possible to filter out and not log syscalls with tty=(none)? I am looking forward to your kind response. Thank You Regards, Vish