CODEWITHSUNDEEP
c++clinux
jp.ko
jp.ko

Reputation: 35

What is the case where SIG_ERR of Linux signal function can occur?

I would like to know which case is SIG_ERR among the return values ​​of the signal function.

__sighandler_t oldHandler = signal( SIGSEGV, newSignalHandler );
if( oldHandler == SIG_ERR )
{
    // In what case?
}

Upvotes: 1

Views: 584

Answers (1)

Nate Eldredge
Nate Eldredge

Reputation: 57922

The man page for each system call is supposed to list all possible error conditions under the "ERRORS" heading, along with the corresponding values to which errno is set in each case.

The man page for signal(2) shows only:

EINVAL signum is invalid.

This occurs if signum (the first argument) isn't the number of a valid signal, or is either SIGKILL or SIGSTOP which cannot be caught or ignored.

As such, if you have passed SIGSEGV as the first argument, signal() should never fail.

(I initially thought it could also fail if handler was an invalid pointer, but it seems in this case that it just installs the invalid pointer as the handler, and thus will segfault or otherwise misbehave should the signal actually be raised.)

Upvotes: 1

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