I am trying to pass command line parameters using following code
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>
static int nilvar=0;
static int nilvar2=0;
int rollcalls[5];// = {0};
char classname[10];// = "math";
module_param_named (var,nilvar2,int,0644);
module_param (nilvar,int,0644);
module_param_array_named(present,rollcalls,int,5,0644);
module_param_string(subject,classname,10,0644);
int init_module(void)
{
printk(KERN_INFO"1) nilvar = %d\n 2) nilvar2 = %d",nilvar,nilvar2);
printk(KERN_INFO/*NOTICE*/"ROLLCALLS = %d ,%d ,%d ,%d",rollcalls[0],rollcalls[1],rollcalls[2],rollcalls[3]);
printk(KERN_INFO/*DEBUG*/"classname = %s",classname);
return 0;
}
void cleanup_module(void)
{
printk(KERN_INFO "Bye....\n");
}
MODULE_LICENSE("GPL");
after make ,I am passing my arguments by
insmod module1.ko var=5 nilvar=6 present=1 2 3 4 subject=physics
I don't know exactly what is happening but now lsmod shows module used by -2.
(actually no module is dependent on this module)
so where I am wrong ? and if we want to modify all this variables as a structure elements, then how to use module_param() macro for it?
#user3452214, instead of module_param_array_named(present, rollcalls, int, **5**, 0644); use module_param_array_named(present, rollcalls, int, **&count**, 0644); added one more variable i.e. static unsigned int count which keep count of the number written to the array. We need to pass the pointer as explained in the moduleparam.h, thus cannot pass numerical value for this parameter. It works fine!!!. Hope it solves your problem.
/**
* module_param_array_named - renamed parameter which is an array of some type
* #name: a valid C identifier which is the parameter name
* #array: the name of the array variable
* #type: the type, as per module_param()
* #nump: optional pointer filled in with the number written
* #perm: visibility in sysfs
*
* This exposes a different name than the actual variable name. See
* module_param_named() for why this might be necessary.
*/
#define module_param_array_named(name, array, type, nump, perm)
Related
I am trying to write a program that calls upon an [external library (?)] (I'm not sure that I'm using the right terminology here) that I am also writing to clean up a provided string. For example, if my main.c program were to be provided with a string such as:
asdfFAweWFwseFL Wefawf JAWEFfja FAWSEF
it would call upon a function in externalLibrary.c (lets call it externalLibrary_Clean for now) that would take in the string, and return all characters in upper case without spaces:
ASDFFAWEWFWSEFLWEFAWFJAWEFFJAFAWSEF
The crazy part is that I have this working... so long as my string doesn't exceed 26 characters in length. As soon as I add a 27th character, I end up with an error that says
malloc(): corrupted top size.
Here is externalLibrary.c:
#include "externalLibrary.h"
#include <ctype.h>
#include <malloc.h>
#include <assert.h>
#include <string.h>
char * restrict externalLibrary_Clean(const char* restrict input) {
// first we define the return value as a pointer and initialize
// an integer to count the length of the string
char * returnVal = malloc(sizeof(input));
char * initialReturnVal = returnVal; //point to the start location
// until we hit the end of the string, we use this while loop to
// iterate through it
while (*input != '\0') {
if (isalpha(*input)) { // if we encounter an alphabet character (a-z/A-Z)
// then we convert it to an uppercase value and point our return value at it
*returnVal = toupper(*input);
returnVal++; //we use this to move our return value to the next location in memory
}
input++; // we move to the next memory location on the provided character pointer
}
*returnVal = '\0'; //once we have exhausted the input character pointer, we terminate our return value
return initialReturnVal;
}
int * restrict externalLibrary_getFrequencies(char * ar, int length){
static int freq[26];
for (int i = 0; i < length; i++){
freq[(ar[i]-65)]++;
}
return freq;
}
the header file for it (externalLibrary.h):
#ifndef LEARNINGC_EXTERNALLIBRARY_H
#define LEARNINGC_EXTERNALLIBRARY_H
#ifdef __cplusplus
extern "C" {
#endif
char * restrict externalLibrary_Clean(const char* restrict input);
int * restrict externalLibrary_getFrequencies(char * ar, int length);
#ifdef __cplusplus
}
#endif
#endif //LEARNINGC_EXTERNALLIBRARY_H
my main.c file from where all the action is happening:
#include <stdio.h>
#include "externalLibrary.h"
int main() {
char * unfilteredString = "ASDFOIWEGOASDGLKASJGISUAAAA";//if this exceeds 26 characters, the program breaks
char * cleanString = externalLibrary_Clean(unfilteredString);
//int * charDist = externalLibrary_getFrequencies(cleanString, 25); //this works just fine... for now
printf("\nOutput: %s\n", unfilteredString);
printf("\nCleaned Output: %s\n", cleanString);
/*for(int i = 0; i < 26; i++){
if(charDist[i] == 0){
}
else {
printf("%c: %d \n", (i + 65), charDist[i]);
}
}*/
return 0;
}
I'm extremely well versed in Java programming and I'm trying to translate my knowledge over to C as I wish to learn how my computer works in more detail (and have finer control over things such as memory).
If I were solving this problem in Java, it would be as simple as creating two class files: one called main.java and one called externalLibrary.java, where I would have static String Clean(string input) and then call upon it in main.java with String cleanString = externalLibrary.Clean(unfilteredString).
Clearly this isn't how C works, but I want to learn how (and why my code is crashing with corrupted top size)
The bug is this line:
char * returnVal = malloc(sizeof(input));
The reason it is a bug is that it requests an allocation large enough space to store a pointer, meaning 8 bytes in a 64-bit program. What you want to do is to allocate enough space to store the modified string, which you can do with the following line:
char *returnVal = malloc(strlen(input) + 1);
So the other part of your question is why the program doesn't crash when your string is less than 26 characters. The reason is that malloc is allowed to give the caller slightly more than the caller requested.
In your case, the message "malloc(): corrupted top size" suggests that you are using libc malloc, which is the default on Linux. That variant of malloc, in a 64-bit process, would always give you at least 0x18 (24) bytes (minimum chunk size 0x20 - 8 bytes for the size/status). In the specific case that the allocation immediately precedes the "top" allocation, writing past the end of the allocation will clobber the "top" size.
If your string is larger than 23 (0x17) you will start to clobber the size/status of the subsequent allocation because you also need 1 byte to store the trailing NULL. However, any string 23 characters or shorter will not cause a problem.
As to why you didn't get an error with a string with 26 characters, to answer that one would have to see that exact program with the string of 26 characters that does not crash to give a more precise answer. For example, if the program provided a 26-character input that contained 3 blanks, this would would require only 26 + 1 - 3 = 24 bytes in the allocation, which would fit.
If you are not interested in that level of detail, fixing the malloc call to request the proper amount will fix your crash.
this is a simple linux kernel module code to reverse a string which should Oops after insmod,but it works well,why?
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
static char *words = "words";
static int __init words_init(void)
{
printk(KERN_INFO "debug info\n");
int len = strlen(words);
int k;
for ( k = 0; k < len/2; k++ )
{
printk("the value of k %d\n",k);
char a = words[k];
words[k]= words[len-1-k];
words[len-1-k]=a;
}
printk(KERN_INFO "words is %s\n", words);
return 0;
}
static void __exit words_exit(void)
{
printk(KERN_INFO "words exit.\n");
}
module_init(words_init);
module_exit(words_exit);
module_param(words, charp, S_IRUGO);
MODULE_LICENSE("GPL");
static != const.
static in your example means "only visible in the current file". See What does "static" mean?
const just means "the code which can see this declaration isn't supposed to change the variable". But in certain cases, you can still create a non-const pointer to the same address and modify the contents.
Space removal from a String - In Place C style with Pointers suggests that writing to the string value shouldn't be possible.
Since static is the only difference between your code and that of the question, I looked further and found this: Global initialized variables declared as "const" go to text segment, while those declared "Static" go to data segment. Why?
Try static const char *word, that should do the trick.
Haha!,I get the answer from the linux kernel source code by myself;When you use the insmod,it will call the init_moudle,load_module,strndup_usr then memdup_usr function;the memdup_usr function will use kmalloc_track_caller to alloc memery from slab and then use the copy_from_usr to copy the module paragram into kernel;this mean the linux kernel module paragram store in heap,not in the constant storage area!! So we can change it's content!
I have the following piece of code in appPOSWebDlg.cpp:
#include "stdafx.h"
#include "afx.h"
#include <stdlib.h>
#include <Ras.h>
...
//Attribute
char *site;
...
// Method
int readFile() {
char * aux;
int result;
result = readParameter(hFile, aux);
if (result == 0) {
memcpy(site, aux, 256);
} else {
return 1;
}
return 0;
}
But the program stops at the memcpy line and I'm not sure why. After debugging, I can confirm that the aux parameter is being assigned correctly with the value expected. Furthermore, I even used the memcpy inside the readParameter method to assign it and had no problem. So why can't I assign that value to attribute site using the same method?
Your "site" pointer is invalid. You've defined it as a pointer, but, not allocated any space for it, so, your copy command is overlaying some code. You'll need to allocated the pointer correctly by performing a "new" and a "delete" when you are done.
Here is an excerpt from ntdddisk.h
typedef struct _DISK_GEOMETRY_EX {
DISK_GEOMETRY Geometry; // Standard disk geometry: may be faked by driver.
LARGE_INTEGER DiskSize; // Must always be correct
UCHAR Data[1]; // Partition, Detect info
} DISK_GEOMETRY_EX, *PDISK_GEOMETRY_EX;
What is the point of UCHAR Data[1];? Why not just UCHAR Data; ?
And there are a lot of structures in DDK which have arrays of one element in declarations.
Thanks, thats clear now. The one thing is not clear the implementation of offsetof.
It's defined as
#ifdef _WIN64
#define offsetof(s,m) (size_t)( (ptrdiff_t)&(((s *)0)->m) )
#else
#define offsetof(s,m) (size_t)&(((s *)0)->m)
#endif
How this works:
((s *)0)->m ???
This
(size_t)&((DISK_GEOMETRY_EX *)0)->Data
is like
sizeof (DISK_GEOMETRY) + sizeof( LARGE_INTEGER);
But there is two additional questions:
1)
What type is this? And why we should use & for this?
((DISK_GEOMETRY_EX *)0)->Data
2) ((DISK_GEOMETRY_EX *)0)
This gives me 00000000. Is it convering to the address alignment? interpret it like an address?
Very common in the winapi as well, these are variable length structures. The array is always the last element in the structure and it always includes a field that indicates the actual array size. A bitmap for example is declared that way:
typedef struct tagBITMAPINFO {
BITMAPINFOHEADER bmiHeader;
RGBQUAD bmiColors[1];
} BITMAPINFO, FAR *LPBITMAPINFO, *PBITMAPINFO;
The color table has a variable number of entries, 2 for a monochrome bitmap, 16 for a 4bpp and 256 for a 8bpp bitmap. Since the actual length of the structure varies, you cannot declare a variable of that type. The compiler won't reserve enough space for it. So you always need the free store to allocate it using code like this:
#include <stddef.h> // for offsetof() macro
....
size_t len = offsetof(BITMAPINFO, bmiColors) + 256 * sizeof(RGBQUAD);
BITMAPINFO* bmp = (BITMAPINFO*)malloc(len);
bmp->bmiHeader.biClrUsed = 256;
// etc...
//...
free(bmp);
In my data.h file I have:
typedef struct {
double ***grid;
} Solver;
In my .c file I have
static Solver _solver;
which first makes a call to a function to do some allocation on grid such as
_solver.grid = malloc(....);
//then makes a call to
GS_init(_solver.grid);
The GS_init function is declared in GS.h as:
void GS_init(double ***grid);
When I try to compile, I get two errors:
the struct "<unnamed>" has no field "grid"
GS_init(_solver.grid)
^
and
too many arguments in function call
GS_init(_solver.grid)
^
Any ideas what is going wrong here?
This code compiles with 'gcc -Wall -Werror -c':
data.h
typedef struct
{
double ***grid;
} Solver;
gs.h
extern void GS_init(double ***grid);
gs.c
#include "data.h"
#include "gs.h"
#include <stdlib.h>
static Solver _solver;
void anonymous(void)
{
_solver.grid = malloc(32 * sizeof(double));
GS_init(_solver.grid);
}
Derek asked:
Why does this work? Is it because of the extern keyword?
The 'extern' is not material to making it work, though I always use it.
When I have to flesh out GS_init() in, say compute.c, would I write void GS_init(double ***grid){ //loop over grid[i][j][k] setting to zero }
Sort of...yes, the GS_init() code could do that if the data structure is set up properly, which is going to need more information than there is currently visible in the structure.
For the compiler to process:
grid[i][j][k] = 0.0;
the code has to know the valid ranges for each of i, j, and k; assume the number of rows in each dimension are Ni, Nj, Nk. The data 'structure' pointed to by grid must be an array of Ni 'double **' values - which must be allocated. Each of those entries must point to Nj 'double *' values. So, you have to do more allocation than a single malloc(), and you have to do more initialization than just setting everything to zero.
If you want to use a single array of doubles only, you will have to write a different expression to access the data:
grid[(i * Ni + j) * Nj + k] = 0.0;
And under this scenario, grid would be a simple double * and not a triple pointer.