Why does this example C code run and yet SHOULD either not compile or give a segmentation fault? Post: 303032991

Sponsored Content

Top Forums Programming Why does this example C code run and yet SHOULD either not compile or give a segmentation fault? Post 303032991 by wisecracker on Thursday 28th of March 2019 05:05:27 AM

03-28-2019

Registered User

Thanks Jim...
I only attempted it to see if it was possible, and it DOES give a segmentation fault IF and only IF the 'jmp' goes directly into main() .
BUT it still compiles...

I created this absolute meaningless garbage and it compiles without warnings and errors and look what happens:

Code:

#include <stdio.h>
#include <stdlib.h>

int NUMBER1 = 255;
float NUMBER2 = 3.1415926;
char CHARACTER = 'X';

int test1(int NUMBER1)
{
    __asm__ volatile(
        "nop;"
        "jmp    jump_test2;"
        "nop;");
    NUMBER1 = 123;
    NUMBER2 = 1.414;
    CHARACTER = '!';
    printf("This will never be seen!\n");
    return NUMBER1;
}

float test2(float NUMBER2)
{
    /* The 'test2:' label sits in here. */
    asm(
        "nop;"
        "jump_test2:"
        "nop;");
    NUMBER1 = -65;
    NUMBER2 = 2.718;
    CHARACTER = '?';
    printf("This will be printed.\n");
    printf("%.03f%c\n", NUMBER2, CHARACTER);
    return NUMBER2;
}

int main(int NUMBER1, char **CHARACTER)
{
    NUMBER1 = test1(NUMBER1);
    printf("%d %s\n", NUMBER1, *CHARACTER);
    printf("Hello World!\n");
    return(0);
}

Results on OSX 10.14.3, default bash terminal, gcc 4.2.1.
(IMPORTANT! NOT checked on gcc 2.95.2 or 7.3.0.)

Code:

Last login: Thu Mar 28 08:36:48 on ttys000
AMIGA:amiga~> cd Desktop/Code/C
AMIGA:amiga~/Desktop/Code/C> gcc cross_function_jump.c
AMIGA:amiga~/Desktop/Code/C> cp a.out cross_function_jump
AMIGA:amiga~/Desktop/Code/C> ./cross_function_jump
This will be printed.
2.718?
7 ./cross_function_jump
Hello World!
AMIGA:amiga~/Desktop/Code/C> _

7 ./cross_function_jump is obviously wrong but I have successfully got 'argv[0]'.
I don't care what is happening but compiling AND running without a segmentation fault is is not a fault of the programmer but of the compiler.

Any 'asm()' whether part of compliance or not code should never be allowed to jump out of its own function domain and this was my point entirely.

What I have done I would never use in practice but I would use inline assembly for mission critical stuff inside its own function.

All I wanted to know why these compile and run, garbage results or not.

wisecracker

View Public Profile for wisecracker

Find all posts by wisecracker

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Segmentation Fault

hello all, I tried a program on an array to intialise array elements from the standard input device.it is an integer array of 5 elements.but after entering the 4th element it throws a message called "Segmentation Fault" and returns to the command prompt without asking for the 5th element. ...

2. AIX

Segmentation fault in nsgetcinfo in aix 64-bit c code

Hello, I am running on a AIX5.2 server with Oracle 10g and 9i. My code compiles and works fine in 32-bit mode. The same code compiles in 64-bit and runs good. The program catches CNTRL-C signal to terminate. Only on 64-bit code when i hit CNTRL-C, the program exits with segmentation...

3. UNIX for Dummies Questions & Answers

Compile & Run Java Code

The java program is a part of speech tagger -> The Stanford NLP (Natural Language Processing) Group The goal is to use this script as part of a webpage to tag parts of speech based on a user-inputted string. I have no idea what to do with the files - I'm a complete *nix noob. I tried running...

4. Programming

Segmentation fault.

I'm getting a segmentation fault. I'm new to Linux programming. Thanks so much for all of your input.:eek: #include </usr/include/mysql++/mysql++.h> #include <stdio.h> #include <iostream> #include <sstream> #include <string.h> using namespace std; int outputToImport(const char*...

5. Programming

C code : Segmentation fault

Hi Friends, I have written a small code in C which performs the below operations Task : 1 ) read line by line from a file. 2 ) assuming 3th and 4th fields of the file as GN and GNTO 3 ) The target file should contain all the fields except GNTO. 4...

6. UNIX for Advanced & Expert Users

segmentation fault with ps

What does this mean and why is this happening? $ ps -ef | grep ocular Segmentation fault (core dumped) $ ps -ef | grep ocular Segmentation fault (core dumped) $ ps aux | grep ocular Segmentation fault (core dumped) $ ps Segmentation fault (core dumped) $ pkill okular $ ps...

7. Programming

Using gdb, ignore beginning segmentation fault until reproduce environment segmentation fault

I use a binary name (ie polo) it gets some parameter , so for debugging normally i do this : i wrote script for watchdog my app (polo) and check every second if it's not running then start it , the problem is , if my app , remain in state of segmentation fault for a while (ie 15 ...

8. Programming

This code keeps giving me a segmentation fault why?

#include<stdlib.h> #include <pthread.h> #include "tlpi_hdr.h" #include <stdio.h> static volatile int glob = 0; static struct { pthread_t t1,t2; } *thread; static void * /* Loop 'arg' times incrementing 'glob' */ threadFunc(void *arg) { int loops = *((int *) arg); ...

9. Solaris

Segmentation fault

Hi Guys, I just installed and booted a zone called testzone. When I logged in remotely and tried changing to root user I get this error: "Segmentation fault" Can someone please help me resolve this? Thanks alot

10. Programming

C. To segmentation fault or not to segmentation fault, that is the question.

Oddities with gcc, 2.95.3 for the AMIGA and 4.2.1 for MY current OSX 10.14.1... I am creating a basic calculator for the AMIGA ADE *NIX emulator in C as it does not have one. Below are two very condensed snippets of which I have added the results inside the each code section. IMPORTANT!...

LEARN ABOUT LINUX

putws

putws(3C)                                                  Standard C Library Functions                                                  putws(3C)

NAME

       putws - convert a string of Process Code characters to EUC characters

SYNOPSIS

       #include <stdio.h>
       #include <widec.h>

       int putws(wchar_t *s);

DESCRIPTION

       The  putws()  function  converts  the  Process  Code string (terminated by a (wchar_t)NULL) pointed to by s, to an Extended Unix Code (EUC)
       string followed by a NEWLINE character, and writes it to the standard output stream stdout. It does not write the terminal null character.

RETURN VALUES

       The putws() function returns the number of Process Code characters transformed and written.  It returns EOF if it attempts to  write  to  a
       file that has not been opened for writing.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       |MT-Level                     |MT-Safe                      |
       +-----------------------------+-----------------------------+

SEE ALSO

       ferror(3C), fopen(3C), fread(3C), getws(3C), printf(3C), putwc(3C), attributes(5)

SunOS 5.10                                                          22 Apr 1997                                                          putws(3C)

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Segmentation Fault

Discussion started by: compbug

2. AIX

Segmentation fault in nsgetcinfo in aix 64-bit c code

Discussion started by: sumesh0710

3. UNIX for Dummies Questions & Answers

Compile & Run Java Code

Discussion started by: tguillea

4. Programming

Segmentation fault.

Discussion started by: sepoto