/*
for memory dump and edit via /dev/mem

** Note that any kernel constraints must be removed! ex, CONFIG_STRICT_DEVMEM and etc **

build intruction:

ANDROID_TARGET=android-8
CROSS_COMPILE=${ANDROID_NDK}/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-
SYS_ROOT=${ANDROID_NDK}/platforms/${ANDROID_TARGET}/arch-arm/

${CROSS_COMPILE}gcc --sysroot=${SYS_ROOT} \
                    memedit.c    \
                    -o memedit
*/

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>

int main(int argc, char *argv[]) {
    int has_input;
    unsigned int input;
    char *ignored;
    unsigned long offset;
    int fd;
    unsigned char* mem;

    if (argc < 2) {
        printf("Usage: %s <phys_addr> [input]\n", argv[0]);
        return 0;
    }

    offset = strtoul(argv[1], &ignored, 16);

    if (argc == 3) {
        has_input = 1;
        input = strtoul(argv[2], &ignored, 16);
    } else {
        has_input = 0;
        input = 0;
    }

    fd = open("/dev/mem", O_SYNC | O_RDWR);

    if (fd == 0) {
        printf("Can't open /dev/mem\n");
        return -1;
    }

    mem = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset & (~4095));
    if (mem == NULL || mem == MAP_FAILED) {
        printf("Can't map memory\n");
        return -1;
    }

    printf("/dev/mem[0x%08x] = 0x%08x", offset, *(unsigned int*)&mem[offset & 4095]);

    if (has_input) {
        printf(" <= 0x%08x\n", input);
        *((unsigned int*)&mem[offset & 4095]) = input;
    }
    else {
        printf("\n");
    }

    close(fd);
}