src/pci_handler.cpp

#include "pci_handler.hpp"

#include <fcntl.h>

#include <stdplus/fd/managed.hpp>
#include <stdplus/fd/mmap.hpp>
#include <stdplus/print.hpp>

#include <cstdint>
#include <cstring>
#include <format>
#include <memory>
#include <span>
#include <vector>

namespace bios_bmc_smm_error_logger
{

PciDataHandler::PciDataHandler(uint32_t regionAddress, size_t regionSize,
                               std::unique_ptr<stdplus::fd::Fd> fd) :
    regionSize(regionSize), fd(std::move(fd)),
    mmap(stdplus::fd::MMap(
        *this->fd, regionSize, stdplus::fd::ProtFlags{PROT_READ | PROT_WRITE},
        stdplus::fd::MMapFlags{stdplus::fd::MMapAccess::Shared}, regionAddress))
{}

std::vector<uint8_t> PciDataHandler::read(const uint32_t offset,
                                          const uint32_t length)
{
    if (offset > regionSize || length == 0)
    {
        stdplus::print(stderr,
                       "[read] Offset [{}] was bigger than regionSize [{}] "
                       "OR length [{}] was equal to 0\n",
                       offset, regionSize, length);
        return {};
    }

    // Read up to regionSize in case the offset + length overflowed
    uint32_t finalLength =
        (offset + length < regionSize) ? length : regionSize - offset;
    std::vector<uint8_t> results(finalLength);

    // Use a volatile pointer to ensure every access reads directly from the
    // memory-mapped region, preventing compiler optimizations like caching.
    const volatile uint8_t* src =
        reinterpret_cast<volatile const uint8_t*>(mmap.get().data() + offset);

    // Perform a byte-by-byte copy to avoid undefined behavior with memcpy on
    // volatile memory.
    for (uint32_t i = 0; i < finalLength; ++i)
    {
        results[i] = src[i];
    }
    return results;
}

uint32_t PciDataHandler::write(const uint32_t offset,
                               const std::span<const uint8_t> bytes)
{
    const size_t length = bytes.size();
    if (offset > regionSize || length == 0)
    {
        stdplus::print(stderr,
                       "[write] Offset [{}] was bigger than regionSize [{}] "
                       "OR length [{}] was equal to 0\n",
                       offset, regionSize, length);
        return 0;
    }

    // Write up to regionSize in case the offset + length overflowed
    uint16_t finalLength =
        (offset + length < regionSize) ? length : regionSize - offset;
    // Use a volatile pointer to ensure every access writes directly to the
    // memory-mapped region.
    volatile uint8_t* dest =
        reinterpret_cast<volatile uint8_t*>(mmap.get().data() + offset);

    // Perform a byte-by-byte copy to ensure volatile semantics.
    for (uint16_t i = 0; i < finalLength; ++i)
    {
        dest[i] = bytes[i];
    }
    return finalLength;
}

uint32_t PciDataHandler::getMemoryRegionSize()
{
    return regionSize;
}

} // namespace bios_bmc_smm_error_logger