How to determine if a function is using a system call
I am learning about system calls and starting to understand them. I understand that you shouldn't call them directly (as this makes your code less portable) and you should call the API instead. However, is there a way to determine if a particular function is using a system call? I read that not all functions require system calls (some library functions). For example fopen will end up using a system call. My questions:
Is cin (c ++) function required for system call
Is there a way to find out if a function is using a system call?
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GDB has a "break on syscall" feature. See https://sourceware.org/gdb/onlinedocs/gdb/Set-Catchpoints.html
So, the strategy, if you're new to debugging tools, is to set a catch point and step down the line that calls the function ("next" in gdb). If it breaks before it reaches the line after the function call, then a system call has occurred (or the program crashed, I suppose).
When you read the input using
cin >> ...
, syscall may or may not be called. It depends on whether there is already enough data in the buffer. If there is not enough data in the buffer, a syscall must be performed to retrieve data from the main file or device.
The C ++ language does not provide an easy built-in way to statically determine whether a function can make a system call. In fact, a function
can call some function
that will be compiled separately (in a different translation unit), which calls a system call; the fact that
can indirectly cause a system call cannot be known until reference time.
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