SIGSEGV on memory access in Beaglebone Black (ARM) cross-compilation w/ Eclipse - Linaro - eclipse

Question

I am new to this, or better rusted (being 62).
Trying to develop on Beaglebone Black running Debian over IP using Eclipse Luna CDT and linaro tools.
I succeed in running and debugging standard helloworld.c.
Need to control GPIO fast (to connect to uncommon peripheral) but
all attempts to read or write to memory mapped registers fail.
Instruction
i = (*((volatile unsigned int *)(0x4804c130)))
which should read GPIO status register results in
Child terminated with signal = 0xb (SIGSEGV)
GDBserver exiting
logout
This is the source (hellobone.c) I compile without errors:
int main(void)
{
unsigned int i = 1;
i = (*((volatile unsigned int *)(0x4804c130))) ;
}
(I tried all variations on this pointer arithmetic)
Makefile trace: (ignore includes)
---COMPILE--- C:/hellobone/source/hellobone.c
"C:\gcc-linaro\bin\arm-linux-gnueabihf-gcc.exe" -c -o C:/hellobone/object/hellobone.o C:/hellobone/source/hellobone.c -marm -O0 -g -I. -IC:/hellobone/include
.
---LINK---
"C:\gcc-linaro\bin\arm-linux-gnueabihf-gcc.exe" -o hellobone C:/hellobone/object/hellobone.o C:/hellobone/object/tools.o C:/hellobone/object/gpio_v2.o -marm -O0 -g -I. -IC:/hellobone/include
.
The binary also crashes running as root from TTY:
root#beaglebone:~# ./hellobone
Segmentation fault
I installed Eclipse on the BBB Debian and read and write to memory works just fine. Just too slow compiling, and unstable, to be practical.
Reading memory should be doable. What am I doing wrong?
I suspect
GNU gdbserver (GDB) 7.4.1-debian
This gdbserver was configured as "arm-linux-gnueabihf"
But maybe I am missing something obvious, have not seen any post on this problem...
Really stuck. Being working on this for months now. Setting up toolchain very frustrating, nothing works as in YouTube videos..
Any help would be really appreciated
Marco

Answer 1

You need to mmap /dev/mem to access memory mapped peripherals through physical addresses. Easiest example / code I know does this goes by the name devmem2.

Answer 2

Thank you a lot, that certainly helped.
I compiled the program you gave me and it worked perfect in run mode in Eclipse, and in terminal on the remote machine.
Curiously, when running the Eclipse debugger, it crashes executing:
if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
I get this error message from gdbserver
Remote debugging from host 192.168.1.2
/root/hellobone: relocation error: /root/hellobone: symbol �pen, version GLIBC_2.4 not defined in file libc.so.6 with link time reference
Child exited with status 127
GDBserver exiting
Have been trying to use fopen but that gives a segmentation fault. Anyhow, I think that is a toolchain issue and not a programming issue.