Hi, I had trouble compiling code with -std=c99 and needed some time to figure out why the use of SA_RESTART did not work with #define _POSIX_C_SOURCE 200112L despite the man page of sigaction suggesting that this would be the correct feature test macro. Searching around the net reveals that this is a known discrepancy between man pages and glibc since at least 11 years. People stumble over this, learn, forget. Please let's document it this time;-) sigaction(2) claims this: POSIX.1-2001 added .BR SA_NOCLDSTOP , .BR SA_NOCLDWAIT , .BR SA_NODEFER , .BR SA_ONSTACK , .BR SA_RESETHAND , .BR SA_RESTART , and .BR SA_SIGINFO . All of these are extensions (XSI) to POSIX and need _XOPEN_SOURCE 600. Quoting https://pubs.opengroup.org/onlinepubs/009695399/basedefs/signal.h.html (thanks to https://unix.stackexchange.com/questions/613139/sigaction-sa-flags-and-posix-1-2001-base-spec): The following shall be declared as constants: SA_NOCLDSTOP [CX] [Option Start] Do not generate SIGCHLD when children stop [Option End] [XSI] [Option Start] or stopped children continue. [Option End] [...] SA_ONSTACK [XSI] [Option Start] Causes signal delivery to occur on an alternate stack. [Option End] SA_RESETHAND [XSI] [Option Start] Causes signal dispositions to be set to SIG_DFL on entry to signal handlers. [Option End] SA_RESTART [XSI] [Option Start] Causes certain functions to become restartable. [Option End] SA_SIGINFO [XSI] [Option Start] Causes extra information to be passed to signal handlers at the time of receipt of a signal. [Option End] SA_NOCLDWAIT [XSI] [Option Start] Causes implementations not to create zombie processes on child death. [Option End] SA_NODEFER [XSI] [Option Start] Causes signal not to be automatically blocked on entry to signal handler. [Option End] [and not mentioned in the man page, not relevant?] SS_ONSTACK [XSI] [Option Start] Process is executing on an alternate signal stack. [Option End] SS_DISABLE [XSI] [Option Start] Alternate signal stack is disabled. [Option End] MINSIGSTKSZ [XSI] [Option Start] Minimum stack size for a signal handler. [Option End] SIGSTKSZ [XSI] [Option Start] Default size in bytes for the alternate signal stack. [Option End] As a related bit, I noticed that feature_test_macros(7) is a bit misleading here: .IP \[bu] Defining .B _XOPEN_SOURCE with a value of 600 or greater produces the same effects as defining .B _POSIX_C_SOURCE with a value of 200112L or greater. As written later on the same page, X_OPEN_SOURCE 600 triggers a superset of POSIX, not the same effects. I hope these rather small changes can be made by a committer without lengthy discussion of patches. I suggest something along this, without formatting details that I'd get wrong: sigaction(2): POSIX.1-2001 added .BR SA_NOCLDSTOP , .BR SA_NOCLDWAIT , .BR SA_NODEFER , .BR SA_ONSTACK , .BR SA_RESETHAND , .BR SA_RESTART , and .BR SA_SIGINFO , as XSI extensions (define _XOPEN_SOURCE to at least 600 to use). feature_test_macros(7): .IP \[bu] Defining .B _XOPEN_SOURCE with a value of 600 or greater includes the effects of defining .B _POSIX_C_SOURCE with a value of 200112L or greater, adding the X/Open System Interfaces Extension (XSI). Alrighty then, Thomas -- GPG public key 60D5CAFE: https://thomas.orgis.org/public_key Fingerprint: D021 FF8E CF4B E097 19D6 1A27 231C 4CBC 60D5 CAFE And despite all of you, I'm still doing it. Yes, I do write Perl code.
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