Some syscalls can be used by malware for more specific purposes, for example, self-defense:
- signal: This can be used to set a new handler for a particular signal and then invoke it to disrupt debugging, for example, for SIGTRAP, which is commonly used for breakpoints
- ptrace: This syscall is commonly used by debugging tools in order to trace executable files, but it can also be used by malware to detect their presence or to prevent them from doing it by tracing itself
Of course, there are many more syscalls, and the sample you're working on may use many of them in order to operate properly. The selection that's been provided describes some of the top picks that may be worth paying attention to when understanding malware functionality.