Segmentation Fault error while running C program [closed] - c

Question

Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 1 year ago.
Improve this question
I'm new using Valgrind for the first time to check memory errrors. I'm running C program and seeing the errors that are not related to the C program but all the errors are from memory (open64.c:48, _IO_file_open (fileops.c:189), .....). I don't know where these files are located. Could you please help me how to resolve this?
==40910== Memcheck, a memory error detector
==40910== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==40910== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==40910== Command: ./dd
==40910==
==40910== Syscall param openat(filename) points to unaddressable byte(s)
==40910== at 0x4ABCEAB: open (open64.c:48)
==40910== by 0x4A3F195: _IO_file_open (fileops.c:189)
==40910== by 0x4A3F459: _IO_file_fopen##GLIBC_2.2.5 (fileops.c:281)
==40910== by 0x4A31B0D: __fopen_internal (iofopen.c:75)
==40910== by 0x4A31B0D: fopen##GLIBC_2.2.5 (iofopen.c:86)
==40910== by 0x109336: main (in /home/Desktop/dd)
==40910== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==40910==
==40910== Invalid read of size 4
==40910== at 0x4A317D7: fgets (iofgets.c:47)
==40910== by 0x109427: main (in /home/Desktop/dd)
==40910== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==40910==
==40910==
==40910== Process terminating with default action of signal 11 (SIGSEGV)
==40910== Access not within mapped region at address 0x0
==40910== at 0x4A317D7: fgets (iofgets.c:47)
==40910== by 0x109427: main (in /home/Desktop/dd)
==40910== If you believe this happened as a result of a stack
==40910== overflow in your program's main thread (unlikely but
==40910== possible), you can try to increase the size of the
==40910== main thread stack using the --main-stacksize= flag.
==40910== The main thread stack size used in this run was 16777216.
==40910==
==40910== HEAP SUMMARY:
==40910== in use at exit: 984 bytes in 3 blocks
==40910== total heap usage: 4 allocs, 1 frees, 1,456 bytes allocated
==40910==
==40910== LEAK SUMMARY:
==40910== definitely lost: 0 bytes in 0 blocks
==40910== indirectly lost: 0 bytes in 0 blocks
==40910== possibly lost: 0 bytes in 0 blocks
==40910== still reachable: 984 bytes in 3 blocks
==40910== suppressed: 0 bytes in 0 blocks
==40910== Rerun with --leak-check=full to see details of leaked memory
==40910==
==40910== For lists of detected and suppressed errors, rerun with: -s
==40910== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
Segmentation fault (core dumped)

Answer 1

Without the code this is certainly the easiest question to answer!
"unaddressable" = point to byte that do not belong to you.
valgrind warns you because probably the memory that you freed in memory is not yours (or, at least, it is no longer reserved for the use you had asked for), and then you could be using it for another thing and interpret a value that is not.
Why doesn't it break when you run without valgrind? Good, for starters - that's what you say. For onething your code is not doing appropriate error checking. So it may be breaking inside, so you wont notice it. All I could say is bad coding style may compile and runs without showing you any errors but in the background it maybe suffocating itself or the thing which it is running on.
Address 0x0 is not stack'd, malloc'd or (recently) free'd`
tells you you're dereferencing a NULL pointer (Address 0x0 ...) meaning fopen failed and returned 0/NULL.
Try fixing it? like..
-Check if returned fopen() valid FILE* to avoid undefined behavior when trying to read from input_file.
-Make sure that if fgets() succeeds (does not return NULL) to avoid undefined behavior.
PS: Read "The 8 Commandments for C Programmers"
2. Thou shalt not follow the NULL pointer, for chaos and madness await thee at its end.
6. If a function be advertised to return an error code in the event of difficulties, thou shalt check for that code, yea, even though the checks triple the size of thy code and produce aches in thy typing fingers, for if thou thinkest “it cannot happen to me”, the gods shall surely punish thee for thy arrogance.

Answer 2

Address 0x0 is not stack'd, malloc'd or (recently) free'd
That means you are using a NULL pointer ( NULL = (void*)0 AND 0 = 0x0 in hexadecimal). Try check if a pointer is NULL before using it.
Edit: if you are using "fopen", this function returns NULL if it cannot open the file.