#include <stdio.h>
#include <stdint.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <asm-x86/msr.h>

#define MSR_ADDR 0xC0011002

// Function to read an MSR
uint64_t read_msr(int fd, uint32_t msr) {
    uint64_t value;
    if (pread(fd, &value, sizeof(value), msr) != sizeof(value)) {
        perror("Error reading MSR");
        return -1;
    }
    return value;
}

// Function to write an MSR
void write_msr(int fd, uint32_t msr, uint64_t value) {
    if (pwrite(fd, &value, sizeof(value), msr) != sizeof(value)) {
        perror("Error writing MSR");
    }
}

// Function to modify bit 18 of MSR 0xC0011002
void set_msr_bit_18(int fd, int set) {
    uint64_t msr_value = read_msr(fd, MSR_ADDR);
    if (msr_value == (uint64_t)-1) {
        return; // Error reading MSR
    }

    if (set) {
        // Set bit 18
        msr_value |= (1ULL << 18);
    } else {
        // Clear bit 18
        msr_value &= ~(1ULL << 18);
    }

    write_msr(fd, MSR_ADDR, msr_value);
}

int supports_rdseed() {
    uint32_t eax, ebx, ecx, edx;
    __asm__ (
        "cpuid"
        : "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx)
        : "a" (0x7), "c" (0)
    );

    return ebx; // Check bit 18 (RDSEED flag)
}

uint32_t rdseed() {
    uint32_t result;
    // Inline assembly to use RDSEED instruction
    __asm__ __volatile__ (
        "rdseed %0" // RDSEED instruction, stores result in result
        : "=r" (result) // Output operand
        : // No input operands
        : "memory" // Clobbered register
    );
    return result;
}

int main()
{
    //you need to disable each core or limit program to run at one core

    int msr_fd = open("/dev/cpu/0/msr", O_RDWR);
    if (msr_fd == -1) {
        perror("Error opening msr");
        return 1;
    }

    printf("RDSEED flag 0x%08x %u\n", supports_rdseed() , (supports_rdseed() >> 18) & 1 );

//    set_msr_bit_18(msr_fd, 1);

    printf("RDSEED flag 0x%08x %u\n", supports_rdseed() , (supports_rdseed() >> 18) & 1 );

    set_msr_bit_18(msr_fd, 0);

    printf("RDSEED flag 0x%08x %u\n", supports_rdseed() , (supports_rdseed() >> 18) & 1 );

    uint32_t random_value = rdseed();
    printf("Random number: %u\n", random_value);

    return 0;
}