WEXITSTATUS(stat_val): … this macro evaluates to the low-order 8 bits of

The status values are retrieved by macros, rather than given as specific bit encodings as they are in most historical implementations (and thus expected by existing programs). This was necessary to eliminate a

#7229: Detecting if a process was killed by a signal is impossible --------------------------------------+------------------------------------ Reporter: benmachine | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: libraries/process | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: --------------------------------------+------------------------------------ Comment (by andersk): Wikipedia is confused. If you go actually read the [http://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html specification], you see the status argument that the child process passed to _exit() or exit(), or the value the child process returned from main(). and also limitation on the number of signals an implementation can support that was inherent in the traditional encodings. Here’s the [https://sourceware.org/git/?p=glibc.git;a=blob;f=bits/waitstatus.h;hb=refs/t... definition] from glibc: {{{ /* If WIFEXITED(STATUS), the low-order 8 bits of the status. */ #define __WEXITSTATUS(status) (((status) & 0xff00) >> 8) /* If WIFSIGNALED(STATUS), the terminating signal. */ #define __WTERMSIG(status) ((status) & 0x7f) }}} which is to say that bits 8-15 of the wait()/waitpid() status are bits 0-7 of the exit() status (the rest of the exit() status being thrown away), and bits 0-6 of the wait()/waitpid() status are the signal number. This agrees with the Perl/Python encoding (because, of course, that’s where the Perl/Python encoding came from). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7229#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler