fxos/lib/os.cpp

#include <fxos/os.h>
#include <fxos/vspace.h>
#include <fxos/memory.h>
#include <fxos/util/log.h>

#include <stdexcept>
#include <cstring>

namespace FxOS {

OS::OS(VirtualSpace &space): type {UNKNOWN}, m_space {space}
{
    if(!space.covers(0x80000000, (256 << 10))) {
        FxOS_log(ERR,
            "OS analysis failed: space doesn't have at least 256 kB "
            "of ROM to analyze from");
        return;
    }

    /* Detect OS type by heuristic */
    if(space.read_str(0x80010000, 8).value == "CASIOWIN")
        this->type = FX;
    else if(space.read_str(0x80020000, 8).value == "CASIOWIN")
        this->type = CG;
    else {
        FxOS_log(ERR, "OS analysis failed: cannot determine OS type");
        return;
    }

    parse_header();
    parse_syscall_table();
    parse_footer();
}

void OS::parse_header()
{
    VirtualSpace &s = m_space;

    if(this->type == FX) {
        /* Bootcode timestamp at the very end of the bootcode */
        this->bootcode_timestamp = s.read_str(0x8000ffb0, 14);
        this->bootcode_checksum = s.read_u32(0x8000fffc);
        this->version = s.read_str(0x80010020, 10);
        this->serial_number = s.read_str(0x8000ffd0, 8);
    }
    else if(this->type == CG) {
        this->bootcode_timestamp = s.read_str(0x8001ffb0, 14);
        this->bootcode_checksum = s.read_u32(0x8001fffc);
        this->version = s.read_str(0x80020020, 10);
        this->serial_number = s.read_str(0x8001ffd0, 8);
    }

    /* Version has format MM.mm.pppp */
    version_major = std::stoi(this->version.value.substr(0, 2));
    version_minor = std::stoi(this->version.value.substr(3, 2));
    version_patch = std::stoi(this->version.value.substr(6, 4));
}

bool OS::version_lt(int major, int minor, int patch) const noexcept
{
    if(this->version_major < major)
        return true;
    if(this->version_major > major)
        return false;
    if(this->version_minor < minor)
        return true;
    if(this->version_minor > minor)
        return false;
    return (this->version_patch < patch);
}

bool OS::version_le(int major, int minor, int patch) const noexcept
{
    if(this->version_major < major)
        return true;
    if(this->version_major > major)
        return false;
    if(this->version_minor < minor)
        return true;
    if(this->version_minor > minor)
        return false;
    return (this->version_patch <= patch);
}

bool OS::version_gt(int major, int minor, int patch) const noexcept
{
    if(this->version_major < major)
        return false;
    if(this->version_major > major)
        return true;
    if(this->version_minor < minor)
        return false;
    if(this->version_minor > minor)
        return true;
    return (this->version_patch > patch);
}

bool OS::version_ge(int major, int minor, int patch) const noexcept
{
    if(this->version_major < major)
        return false;
    if(this->version_major > major)
        return true;
    if(this->version_minor < minor)
        return false;
    if(this->version_minor > minor)
        return true;
    return (this->version_patch >= patch);
}

//---
// Syscall resolution
//---

int OS::syscall_count() const noexcept
{
    return m_syscall_table.size();
}

uint32_t OS::syscall(int id) const
{
    return m_syscall_table[id];
}

int OS::find_syscall(uint32_t entry) const noexcept
{
    try {
        return m_syscall_addresses.at(entry);
    }
    catch(std::out_of_range &e) {
        return -1;
    }
}

uint32_t OS::syscall_table_address() const noexcept
{
    uint32_t address = (this->type == FX) ? 0x8001007c : 0x8002007c;
    return m_space.read_u32(address);
}

void OS::parse_syscall_table()
{
    /* Traverse the syscall table */
    uint32_t syscall_table = syscall_table_address();
    int id = 0;

    while(1) {
        uint32_t entry = m_space.read_u32(syscall_table + 4 * id);

        MemoryRegion const *r = MemoryRegion::region_for(entry);
        if(!r)
            break;

        m_syscall_table.push_back(entry);
        m_syscall_addresses[entry] = id;

        id++;
    }
}

//---
// Footer search
//---

void OS::parse_footer()
{
    VirtualSpace &s = m_space;

    /* Find the footer address (occurrence of "CASIOABSLangdata") */
    uint32_t start = MemoryRegion::ROM.start;
    uint32_t end = MemoryRegion::ROM.end;

    this->footer = s.search(start, end, "CASIOABSLangdata", 16);
    if(this->footer == end) {
        this->footer = -1;
        this->timestamp = std::string("");
        this->langdata = 0;
        this->computed_checksum = -1;
        return;
    }

    uint32_t addr = this->footer + 8;
    this->langdata = 0;

    while(1) {
        void const *entry = s.translate(addr, 8);
        if(!entry || memcmp(entry, "Langdata", 8) != 0)
            break;
        this->langdata++;
        addr += 0x30;
    }

    this->timestamp = s.read_str(addr, 14);
    this->checksum = s.read_u32(addr + 0x18);
    this->computed_checksum = this->compute_checksum();
}

//---
// Checksum
//---

static uint32_t accumulate_range(
    VirtualSpace &m_space, uint32_t start, uint32_t end)
{
    uint32_t sum = 0;

    /* Read from dynamically-sized bindings; read_u8() would be too slow */
    while(start < end) {
        int size;
        uint8_t *buf = (uint8_t *)m_space.translate_dynamic(start, &size);
        if(!buf || size <= 0)
            return -1;

        if(start + size > end)
            size = end - start;

        for(int i = 0; i < size; i++)
            sum += buf[i];

        start += size;
    }

    return sum;
}

uint32_t OS::compute_checksum() const
{
    if(this->type == FX) {
        return accumulate_range(m_space, 0x80010000, this->checksum.address);
    }
    else if(this->type == CG) {
        if(this->version_lt(2, 2, 0)) {
            return accumulate_range(m_space, 0x80020000, 0x80b5feb0)
                   + accumulate_range(m_space, 0x80b5fef0, 0x80b5fff8);
        }
        else {
            return accumulate_range(m_space, 0x80020000, 0x80b20000)
                   + accumulate_range(
                       m_space, this->footer + 8, this->checksum.address);
        }
    }
    return -1;
}

} /* namespace FxOS */