GDB throws cryptic error when invoked from NSTask

Question

Im trying to use NSTask to invoke GDB, the variable "resultStringID" is actually the corresponding process ID and "abc" is just an NSString. My code for invoking GDB is as follows

NSMutableString *resultStringID = [NSMutableString stringWithCapacity:processSelected.length];

        NSScanner *scanner = [NSScanner scannerWithString:processSelected];  
        //define the allowed characters, here only all numbers are allowed 
        NSCharacterSet *allowedChars = [NSCharacterSet characterSetWithCharactersInString:@"1234567890"]; 

        while ([scanner isAtEnd] == NO) {  
            NSString *buffer;  
            if ([scanner scanCharactersFromSet:allowedChars intoString:&buffer]) {  
                [resultStringID appendString:buffer];       
            } else {  
                [scanner setScanLocation:([scanner scanLocation] + 1)];  
            }  
        }  

        //Trim off the last 3 characters if the string is larger than 4 characters long
        if ( [resultStringID length] > 4 )
            resultStringID = [resultStringID substringToIndex:[resultStringID length] - 3];


        NSInteger pid1 = [resultStringID intValue];

        //NSLog(@"pid 1 is :%@", pid1);

        NSTask *task = [[NSTask alloc] init];
        [task setLaunchPath: @"/usr/bin/gdb"];

        NSString * abc = @"abc";



        //NSLog(@"Process with extension %@", fullString);

        NSArray *arguments;
        arguments = [NSArray arrayWithObjects: abc, resultStringID, nil];
        [task setArguments: arguments];

        NSPipe *pipe;
        pipe = [NSPipe pipe];
        [task setStandardOutput: pipe];

        NSFileHandle *file;
        file = [pipe fileHandleForReading];

        [task launch];

        NSData *data;
        data = [file readDataToEndOfFile];

        NSString *string;
        string = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];
        NSLog (@"GDB Output:\n%@", string);

        /*
        GDBViewController *bController = [[GDBViewController alloc] init];
        [self.navigationController pushViewController:bController animated:YES];
        [bController release];
        */

        TableViewController_09AppDelegate *appDelegate = (TableViewController_09AppDelegate*)[[UIApplication sharedApplication] delegate];


        [string release];
        [task release];

Any help is very much appreciated! :)

The output of the task launch looks like this :

RE:Notice: Launching: com.apple.gdb
abc: No such file or directory 
//763: No such file or directory
Unable to access task for process-id 763: (os/kern) failure.
2011-08-24 08:53:06.002 TableViewController_09[764:507] GDB Output:
GNU gdb 6.3.50.20050815-cvs (Fri Mar 18 17:42:37 UTC 2011)
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "--host=arm-apple-darwin9 --target="...
(gdb) Exception condition detected on fd 0
error detected on stdin

What error do you get and what line of code throws it? We can't solve the problem if we don't know what it is. — TechZen
I posted the output GDB gives when its deployed on the iPhone already — Jared Aaron Loo
What are you expecting to happen if you don't give GDB a standard input? — jtbandes
My main aim is to display the output of the GDB command in a view. When I add a standard input NSPipe like this : NSPipe *pipe1; pipe1 = [NSPipe pipe]; [task setStandardInput:pipe1]; My simulator just hangs until I exit it — Jared Aaron Loo

jtbandes jtbandes · Accepted Answer · 2011-08-24T02:00:16

The line error detected on stdin indicates that there's no standard input to the process. You have set up an NSPipe for standard output, why not also set one up for standard input?

GDB throws cryptic error when invoked from NSTask

2 Answers