global-buffer-overflow with C-Fortran interface

Question

So, I am writing a Fortran code and I wanted to get the full path of the input file and I wrote the following code with c interface

C code:

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



void realpathFunc(char * argc, char * output, int * n){ 
    realpath(argc, output);
    *n = strlen(output);
}

Fortran code:

module sysUtils
    !! Routines for different system utilities
    use iso_c_binding, only : c_char, c_int
    use iso_fortran_env, only: error_unit

    private :: error_unit
    interface
        subroutine getFullPath_s(rPath, aPath, n) bind(c, name='realpathFunc')
            !! Resolve absolute path from a relative path
            import :: c_char, c_int
            character(kind=c_char) :: rPath(*), aPath(*)
            integer(kind=c_int) :: n
        end subroutine
    end interface

    contains

    character(len=200) function getFullPath(relativePath) result(actualPath)
        !! Resolve absolute path from a relative path
        character(len=*) :: relativePath
        integer :: n
        call getFullPath_s(relativePath, actualPath, n)
        actualPath(n+1:) = ''
    end 

end module

Main code:

program main
use sysUtils

print *, getFullPath('myFile')

end

When I execute this with gfortran( gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)) with flags -g -Wall -Wextra -Wconversion -g -fbacktrace -fbounds-check -ffpe-trap=zero,overflow,underflow -fsanitize=address,undefined, the following error is thrown

  #0 0x1553e213e86c  (/lib/x86_64-linux-gnu/libasan.so.5+0x8086c)
    #1 0x55ef197ac2e3 in realpathFunc (/folder/a.out+0x22e3)
    #2 0x55ef197ac3b8 in __sysutils_MOD_getfullpath /folder/utils.f90:23
    #3 0x55ef197ac840 in MAIN__ /folder/main.f90:5
    #4 0x55ef197ac99a in main /folder/main.f90:2
    #5 0x1553e12be0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #6 0x55ef197ac1fd in _start (/folder/a.out+0x21fd)

0x55ef197ad2a2 is located 0 bytes to the right of global variable '*.LC2' defined in 'main.f90' (0x55ef197ad2a0) of size 2
0x55ef197ad2a2 is located 62 bytes to the left of global variable 'options.2' defined in 'main.f90:2' (0x55ef197ad2e0) of size 28
SUMMARY: AddressSanitizer: global-buffer-overflow (/lib/x86_64-linux-gnu/libasan.so.5+0x8086c) 
Shadow bytes around the buggy address:
  0x0abe632eda00: 00 00 00 00 00 02 f9 f9 f9 f9 f9 f9 00 00 00 00
  0x0abe632eda10: 00 00 00 00 00 00 00 00 00 04 f9 f9 f9 f9 f9 f9
  0x0abe632eda20: 00 00 00 05 f9 f9 f9 f9 f9 f9 f9 f9 00 00 00 00
  0x0abe632eda30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0abe632eda40: 00 00 00 00 00 00 00 00 00 00 00 00 00 01 f9 f9
=>0x0abe632eda50: f9 f9 f9 f9[02]f9 f9 f9 f9 f9 f9 f9 00 00 00 04
  0x0abe632eda60: f9 f9 f9 f9 00 00 00 00 00 00 00 00 00 00 00 00
  0x0abe632eda70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0abe632eda80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0abe632eda90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0abe632edaa0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==918480==ABORTING

Can anyone tell me what am I doing wrong here and how do I solve this error.