Linux/AM3354: Segmentation fault

Jonas Hjulstad

Part Number: AM3354

Tool/software: Linux

Hi!

I've been trying to access the MCSPI0-registers listed in the L4_PER peripheral memory map in the Cortex A8-section.

#include <stdint.h>
#include <stdio.h>
#include <pru_cfg.h>
#define PRU_ICSS_BASE               (*((volatile unsigned int *)(0x00026000)))
#define PRU_ICSS_SYSCFG             (*((volatile unsigned int *)(0x00026004)))
int main(void)
{   
 CT_CFG.SYSCFG_bit.STANDBY_INIT = 0;
}

Trying to access the dereferenced pointers gives segfault, trying to set STANDBY_INIT gives segfault. Why?

over 6 years ago

0 Biser Gatchev-XID over 6 years ago

TI__Guru**** 393215 points

Please provide complete details of your use case: Linux version, what you are trying to do, etc...

0 Wolfgang Muees1 over 6 years ago

Genius 3685 points

You are not allowed to access these memory locations from user space. The MMU gives you a segfault.

You should use/write a kernel driver for access of hardware registers.

0 Jonas Hjulstad over 6 years ago in reply to Biser Gatchev-XID

Prodigy 160 points

I am currently using : BeagleBoard.org Debian Image 2018-10-07 on the BeagleBone Black Wireless, and i am trying to control the mcSPI-module by writing directly to memory from C++.

0 Jonas Hjulstad over 6 years ago in reply to Wolfgang Muees1

Prodigy 160 points

Following Derek Molloys example: ,

i tried to write a loadable kernel module access the hardware registers. This is a hello-world example where I modified two lines marked with ***own modification***

/**
 * @file    hello.c
 * @author  Derek Molloy
 * @date    4 April 2015
 * @version 0.1
 * @brief  An introductory "Hello World!" loadable kernel module (LKM) that can display a message
 * in the /var/log/kern.log file when the module is loaded and removed. The module can accept an
 * argument when it is loaded -- the name, which appears in the kernel log files.
 * @see http://www.derekmolloy.ie/ for a full description and follow-up descriptions.
*/

#include <linux/init.h>             // Macros used to mark up functions e.g., __init __exit
#include <linux/module.h>           // Core header for loading LKMs into the kernel
#include <linux/kernel.h>           // Contains types, macros, functions for the kernel


MODULE_LICENSE("GPL");              ///< The license type -- this affects runtime behavior
MODULE_AUTHOR("Derek Molloy");      ///< The author -- visible when you use modinfo
MODULE_DESCRIPTION("A simple Linux driver for the BBB.");  ///< The description -- see modinfo
MODULE_VERSION("0.1");              ///< The version of the module
volatile unsigned int * McSPI0_HL_HWINFO = 0x48030004;                                                  ***own modification***
static char *name = "world";        ///< An example LKM argument -- default value is "world"
module_param(name, charp, S_IRUGO); ///< Param desc. charp = char ptr, S_IRUGO can be read/not changed
MODULE_PARM_DESC(name, "The name to display in /var/log/kern.log");  ///< parameter description

/** @brief The LKM initialization function
 *  The static keyword restricts the visibility of the function to within this C file. The __init
 *  macro means that for a built-in driver (not a LKM) the function is only used at initialization
 *  time and that it can be discarded and its memory freed up after that point.
 *  @return returns 0 if successful
 */
static int __init helloBBB_init(void){
   printk(KERN_INFO "EBB: Hello %s from the BBB LKM!\n", name);
   printk(KERN_INFO "HWINFO for mcSPI: %d\n", *McSPI0_HL_HWINFO);                                   **own modification**
   return 0;
}

/** @brief The LKM cleanup function
 *  Similar to the initialization function, it is static. The __exit macro notifies that if this
 *  code is used for a built-in driver (not a LKM) that this function is not required.
 */
static void __exit helloBBB_exit(void){
   printk(KERN_INFO "EBB: Goodbye %s from the BBB LKM!\n", name);
}

/** @brief A module must use the module_init() module_exit() macros from linux/init.h, which
 *  identify the initialization function at insertion time and the cleanup function (as
 *  listed above)
 */
module_init(helloBBB_init);
module_exit(helloBBB_exit);

This gives the following error when tailing /var/log/kern.log:

Apr 21 14:56:50 beaglebone kernel: [ 477.507930] Unable to handle kernel paging request at virtual address 48030004
Apr 21 14:56:50 beaglebone kernel: [ 477.524656] pgd = d38c0000
Apr 21 14:56:50 beaglebone kernel: [ 477.527398] [48030004] *pgd=00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.533875] Internal error: Oops: 5 [#1] PREEMPT SMP ARM

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.654330] Process insmod (pid: 2215, stack limit = 0xdb2aa218)

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.660363] Stack: (0xdb2abd78 to 0xdb2ac000)

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.664740] bd60: c1504dc8 bf4bc000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.672958] bd80: db2abe04 db2abd90 c0101d28 bf4bc00c db2aa000 dfd3255c c02cb254 db25fc80

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.681175] bda0: db2aa000 dc001e40 db2abdc0 c02e19f0 db2aa000 dc001e40 db2abe04 db2abdc8

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.689393] bdc0: c02e19f0 c02ee9cc 00000001 00000002 dc4e2800 c01e7978 00000001 77533b88

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.697610] bde0: bf4b9040 00000001 bf4b9040 dc4e2f80 00000001 e0921000 db2abe2c db2abe08

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.705828] be00: c01e79b4 c0101cd0 db2abe2c db2abe18 db2abf3c 00000001 bf4b9040 db25fc00

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.714045] be20: db2abf14 db2abe30 c01e65e0 c01e794c bf4b904c 00007fff bf4b9040 c01e3628

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.722263] be40: dad830c0 c11e27ac bf4b923c c10eec30 c11e0b7c bf4b9170 c0e0811c bf4b9140

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.730480] be60: db2abf3c bf4b9154 d389fcc4 bf4b9040 bf4b9088 c1504dc8 db2abea8 c1205fdc

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.738697] be80: db2abf2c db2abf30 db2abee4 db2abe98 00000000 00000000 00000000 00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.746914] bea0: 00000000 00000000 6e72656b 00006c65 00000000 00000000 00000000 00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.755131] bec0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.763349] bee0: 00000000 77533b88 7fffffff c1504dc8 00000000 00000003 00469294 c01090e4

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.771567] bf00: db2aa000 00000000 db2abfa4 db2abf18 c01e6fc8 c01e43f4 7fffffff 00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.779784] bf20: 00000003 db2abf38 db2abf3c e0921000 00001368 00000000 00000000 e09211c6

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.788002] bf40: e0921000 00001368 e0921e68 e0921d28 e0921aa0 00003000 00003160 00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.796219] bf60: 00000000 00000000 000015c8 0000001d 0000001e 00000015 00000012 0000000e

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.804437] bf80: 00000000 77533b88 d7250400 00000000 0047ae1c 0000017b 00000000 db2abfa8

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.812654] bfa0: c0108f00 c01e6ef8 d7250400 00000000 00000003 00469294 00000000 bec15a70

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.820871] bfc0: d7250400 00000000 0047ae1c 0000017b 00000000 00000000 0047a770 00000000

Message from syslogd@beaglebone at Apr 21 14:56:51 ...
kernel:[ 477.829089] bfe0: bec15a18 bec15a08 004605bb b6e36fc2 60030030 00000003 00000000 00000000

Is there any way to list drivers associated with the memory address? I have tried rrmodding the spidev module, which did not have any effect

0 Jonas Hjulstad over 6 years ago in reply to Jonas Hjulstad

Prodigy 160 points

I found a list of registers used in /proc/iomem, and when grepping "spi" this came as results:
48030000-480303ff : /ocp/spi@48030000
481a0000-481a03ff : /ocp/spi@481a0000

0 Chester Gillon over 6 years ago in reply to Jonas Hjulstad

Guru 92251 points

Jonas Hjulstad said:
I am currently using : BeagleBoard.org Debian Image 2018-10-07 on the BeagleBone Black Wireless, and i am trying to control the mcSPI-module by writing directly to memory from C++.

In the past I have used a userspace I/O system (UIO) driver to give user space access to memory mapped device registers.

See The Userspace I/O HOWTO for an introduction to UIO

https://github.com/Chester-Gillon/nvram_uio is a UIO example, but was written for a PCIe device in a x86_64 PC running a 2.6 series Kernel so not sure how much code can be re-used for Linux running on ARM.

0 Wolfgang Muees1 over 6 years ago in reply to Jonas Hjulstad

Genius 3685 points

Read about ioremap(). There is an online book at www.oreilly.com/.../

0 Jonas Hjulstad over 6 years ago in reply to Wolfgang Muees1

Prodigy 160 points

Thanks for the response!

When trying to use the ioremap-function, i receive an error from one of the includes:

root@beaglebone:~/projects# make
make -C /lib/modules/4.14.71-ti-r80/build/ M=/root/projects modules
make[1]: Entering directory '/usr/src/linux-headers-4.14.71-ti-r80'
  CC [M]  /root/projects/test.o
In file included from /root/projects/test.c:16:0:
/root/projects/test.c: In function ‘helloBBB_init’:
./arch/arm/include/asm/io.h:400:17: error: initializer element is not constant
 #define ioremap ioremap
                 ^
/root/projects/test.c:33:30: note: in expansion of macro ‘ioremap’
  static void __iomem *regs = ioremap(0x48030004, 0xFFF);
                              ^~~~~~~

with code:

#include <linux/init.h>             // Macros used to mark up functions e.g., __init __exit
#include <linux/module.h>           // Core header for loading LKMs into the kernel
#include <linux/kernel.h>           // Contains types, macros, functions for the kernel
#include <linux/version.h>
#include <asm/io.h>
MODULE_LICENSE("GPL");              ///< The license type -- this affects runtime behavior
MODULE_AUTHOR("Derek Molloy");      ///< The author -- visible when you use modinfo
MODULE_DESCRIPTION("A simple Linux driver for the BBB.");  ///< The description -- see modinfo
MODULE_VERSION("0.1");              ///< The version of the module
//volatile unsigned int * McSPI0_HL_HWINFO = 0x48030004;
static char *name = "world";        ///< An example LKM argument -- default value is "world"
module_param(name, charp, S_IRUGO); ///< Param desc. charp = char ptr, S_IRUGO can be read/not changed
MODULE_PARM_DESC(name, "The name to display in /var/log/kern.log");  ///< parameter description

 */
static int __init helloBBB_init(void){
        printk(KERN_INFO "EBB: Hello %s from the BBB LKM!\n", name);
        static void __iomem *regs = ioremap(0x48030004, 0xFFF);

  // printk(KERN_INFO "HWINFO for mcSPI: %d\n", *McSPI0_HL_HWINFO);
   return 0;
}


static void __exit helloBBB_exit(void){
   printk(KERN_INFO "EBB: Goodbye %s from the BBB LKM!\n", name);
}

module_init(helloBBB_init);
module_exit(helloBBB_exit);

0 Jonas Hjulstad over 6 years ago in reply to Jonas Hjulstad

Prodigy 160 points

Splitting the void*-declaration from the ioremap() and placing it by the static char declaration solved the issue

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Linux/AM3354: Segmentation fault