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What is the use of SA_ONSTACK in sigaction?

When the signal is delivered, the signal handler runs on the process stack. If SA_ONSTACK is used in sigaction() , then another stack is used.

What is the use of using another stack? Any use case?

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One use of the alternative stack is to properly handle SIGSEGV .

If your process received only SIGSEGV because it exceeded the stack limit, you cannot start the signal handler in the process stack - it is already full. The presence of an alternative stack allows you to (cautiously) perform more or less graceful completion in this case.

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Another interesting example is when you associate “normal” code, such as C, with some other version of the language using split stacks such as Go.

In Go, goroutines (light streams) have a rather small stack that expands as needed. Basically, each function prolog checks that the stack has enough free space, and increases the stack if it does not.

When Go calls C code through cgo, it automatically expands the stack to meet C expectations.

However, if the C code sets up signal handlers, they can be called at any time, including if there is not enough stack space.

Thus, any C code that references Go code must use SA_ONSTACK so as not to crash.

https://golang.org/pkg/os/signal/#hdr-Go_programs_that_use_cgo_or_SWIG

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Source: https://habr.com/ru/post/1399553/

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