Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: Why does this example C code run and yet SHOULD either not compile or give a segmentation fault?
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
Old 03-28-2019
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.
 

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. ... (3 Replies)
Discussion started by: compbug
3 Replies

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... (0 Replies)
Discussion started by: sumesh0710
0 Replies

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 Replies)
Discussion started by: tguillea
4 Replies

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*... (1 Reply)
Discussion started by: sepoto
1 Replies

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... (3 Replies)
Discussion started by: kiran_bhatter
3 Replies

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... (1 Reply)
Discussion started by: cokedude
1 Replies

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 ... (6 Replies)
Discussion started by: pooyair
6 Replies

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); ... (1 Reply)
Discussion started by: fwrlfo
1 Replies

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 (2 Replies)
Discussion started by: cjashu
2 Replies

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!... (11 Replies)
Discussion started by: wisecracker
11 Replies

LEARN ABOUT CENTOS

seccomp_merge

seccomp_merge(3)					     libseccomp Documentation						  seccomp_merge(3)

NAME

       seccomp_merge - Merge two seccomp filters

SYNOPSIS

       #include <seccomp.h>

       typedef void * scmp_filter_ctx;

       int seccomp_merge(scmp_filter_ctx dst, scmp_filter_ctx src);

       Link with -lseccomp.

DESCRIPTION

       The  seccomp_merge()  function merges the seccomp filter in src with the filter in dst and stores the resulting in the dst filter.  If suc-
       cessfull, the src seccomp filter is released and all internal memory assocated with the filter is freed; there is  no  need  to	call  sec-
       comp_release(3) on src and the caller should discard any references to the filter.

       In order to merge two seccomp filters, both filters must have the same attribute values and no overlapping architectures.

RETURN VALUE

       Returns zero on success and negative values on failure.

EXAMPLES

       #include <seccomp.h>

       int main(int argc, char *argv[])
       {
	    int rc = -1;
	    scmp_filter_ctx ctx_32, ctx_64;

	    ctx_32 = seccomp_init(SCMP_ACT_KILL);
	    if (ctx_32 == NULL)
		 goto out_all;
	    ctx_64 = seccomp_init(SCMP_ACT_KILL);
	    if (ctx_64 == NULL)
		 goto out_all;

	    if (seccomp_arch_exist(ctx_32, SCMP_ARCH_X86) == -EEXIST) {
		 rc = seccomp_arch_add(ctx_32, SCMP_ARCH_X86);
		 if (rc != 0)
		      goto out_all;
		 rc = seccomp_arch_remove(ctx_32, SCMP_ARCH_NATIVE);
		 if (rc != 0)
		      goto out_all;
	    }
	    if (seccomp_arch_exist(ctx_64, SCMP_ARCH_X86_64) == -EEXIST) {
		 rc = seccomp_arch_add(ctx_64, SCMP_ARCH_X86_64);
		 if (rc != 0)
		      goto out_all;
		 rc = seccomp_arch_remove(ctx_64, SCMP_ARCH_NATIVE);
		 if (rc != 0)
		      goto out_all;
	    }

	    /* ... */

	    rc = seccomp_merge(ctx_64, ctx_32);
	    if (rc != 0)
		 goto out_all;

	    /* NOTE: the 'ctx_32' filter is no longer valid at this point */

	    /* ... */

       out:
	    seccomp_release(ctx_64);
	    return -rc;
       out_all:
	    seccomp_release(ctx_32);
	    goto out;
       }

NOTES

       While the seccomp filter can be generated independent of the kernel, kernel support is required to load and enforce the seccomp filter gen-
       erated by libseccomp.

       The libseccomp project site, with more information and the source code repository, can be found at http://libseccomp.sf.net.  This  library
       is currently under development, please report any bugs at the project site or directly to the author.

AUTHOR

       Paul Moore <paul@paul-moore.com>

SEE ALSO

       seccomp_init(3), seccomp_reset(3), seccomp_arch_add(3), seccomp_arch_remove(3), seccomp_attr_get(3), seccomp_attr_set(3)

paul@paul-moore.com						 28 September 2012						  seccomp_merge(3)
All times are GMT -4. The time now is 04:21 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy