/*
 * Copyright 2018, Jérôme Duval, jerome.duval@gmail.com.
 * Distributed under the terms of the MIT License.
 */


#include "arch/x86/arch_altcodepatch.h"

#include <stdlib.h>
#include <string.h>

#include <KernelExport.h>

#include <elf.h>
#include <kernel.h>
#include <vm_defs.h>



typedef struct altcodepatch {
        uint32 kernel_offset;
        uint16 length;
        uint16 tag;
} altcodepatch;


extern altcodepatch altcodepatch_begin;
extern altcodepatch altcodepatch_end;


void
arch_altcodepatch_replace(uint16 tag, void* newcodepatch, size_t length)
{
        uint32 count = 0;

        // we need to write to the text area
        struct elf_image_info* info = elf_get_kernel_image();
        const uint32 kernelProtection = B_KERNEL_READ_AREA | B_KERNEL_EXECUTE_AREA;
        set_area_protection(info->text_region.id, kernelProtection | B_KERNEL_WRITE_AREA);

        const uint8 kNOPs[9][9] = {
                {X86_NOP1}, {X86_NOP2}, {X86_NOP3}, {X86_NOP4}, {X86_NOP5}, {X86_NOP6},
                {X86_NOP7}, {X86_NOP8}, {X86_NOP9}
        };

        for (altcodepatch* patch = &altcodepatch_begin; patch < &altcodepatch_end;
                        patch++) {
                if (patch->tag != tag)
                        continue;
                uint8* address = (uint8*)(KERNEL_LOAD_BASE + patch->kernel_offset);
                if (patch->length < length)
                        panic("can't copy patch: new code is too long\n");

                memcpy(address, newcodepatch, length);
                address += length;

                size_t remainder = patch->length - length;
                while (remainder > 0) {
                        size_t toWrite = min_c(remainder, 9);
                        memcpy(address, kNOPs[toWrite - 1], toWrite);
                        address += toWrite;
                        remainder -= toWrite;
                }

                count++;
        }

        // disable write after patch
        set_area_protection(info->text_region.id, kernelProtection);

        dprintf("arch_altcodepatch_replace found %" B_PRIu32 " altcodepatches "
                "for tag %u\n", count, tag);
}