Return Codes... Post: 302867345

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Top Forums UNIX for Dummies Questions & Answers Return Codes... Post 302867345 by bakunin on Thursday 24th of October 2013 04:26:20 AM

10-24-2013

Registered User

Quote:

Originally Posted by wisecracker

This was just an idea...

I wasn't actually asking anything. I was experimenting with generating an error code
system of my own with values outside of an 8 bit range.
I used the real 255 exit code as 'number out of range' flag and then generate a string
whilst exit is in process. This string was originally a number, but I decided to make it
a string instead, purely for fun.

I am not sure if this will work in any way: return codes are not coming out of thin air, but the result of a system call, as jim mcNamara has explained. It can't give you back more than it ought to. It is defined as an unsigned 8-bit integer, so it can't deliver a 16- (or 32-, 64-, ...) bit number, a string or whatever. This would mean that this value has to be put on the stack and then pulled off it by the wait() or waitpid()-function. As the function would not know that it is expected to get that off the stack it won't do it and the stack would be (and stay) subsequently corrupted.

If you want to have extended exit-messages of any sort - strings, numbers, whatever - you will have to use the classical means of conveying such messages: interprocess communication (aka semaphores, shared memory segments, ... - take your pick) or process-to-process I/O, like file descriptors and/or named pipes. Write to <stdout>, <stderr>, etc. and intercept this with pipes, I/O-redirection and the like.

Another option is to write to a log file of some sort and have that parsed from the calling process.

Quote:

Originally Posted by wisecracker

Perhaps I shouldn't have posted it...

There is no harm done in discussing anything and i am convinced this board won't go down from 1k characters of non-conclusive discussion. Still, i think you should post such topics (and the likes - you seem to enjoy exploring the limits of the OS in general and the shell in specific) not in the beginner forum. This is clearly not the stuff someone who learned the shell yesterday asks first. Please consider moving to the experts forum for topics like this.

I hope this helps.

bakunin

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LEARN ABOUT ULTRIX

sigstack

sigstack(2)							System Calls Manual						       sigstack(2)

Name
       sigstack - set or get signal stack context

Syntax
       #include <signal.h>

       struct sigstack {
       caddr_t	 ss_sp;
       int  ss_onstack;
       };

       sigstack(ss, oss)
       struct sigstack *ss, *oss;

Description
       The  system  call  allows users to define an alternate stack on which signals are to be processed.  If ss is nonzero, it specifies a signal
       stack on which to deliver signals and tells the system if the process is currently executing on that stack.  When a signal's  action  indi-
       cates  its handler should execute on the signal stack (specified with a call), the system checks to see if the process is currently execut-
       ing on that stack.  If the process is not currently executing on the signal stack, the system arranges a switch to the signal stack for the
       duration of the signal handler's execution.  If oss is nonzero, the current signal stack state is returned.

       Signal stacks are not grown'automatically, as is done for the normal stack.  If the stack overflows, unpredictable results may occur.

Return Values
       Upon successful completion, a value of zero (0) is returned.  Otherwise, a value of -1 is returned and errno is set to indicate the error.

Diagnostics
       The system call fails and the signal stack context remains unchanged, if one of the following occurs.

       [EFAULT]       Either ss or oss points to memory that is not a valid part of the process address space.

See Also
       sigvec(2), setjmp(3)

																       sigstack(2)

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