FEX-Emu--FEX/FEXCore/Source/Utils/Allocator.cpp

// SPDX-License-Identifier: MIT
#include "Utils/Allocator/HostAllocator.h"
#include <FEXCore/Utils/Allocator.h>
#include <FEXCore/Utils/CompilerDefs.h>
#include <FEXCore/Utils/LogManager.h>
#include <FEXCore/Utils/TypeDefines.h>
#include <FEXCore/fextl/fmt.h>
#include <FEXCore/fextl/memory_resource.h>
#include <FEXHeaderUtils/Syscalls.h>

#include <array>
#include <cctype>
#include <charconv>
#include <cstdio>
#include <fcntl.h>
#ifndef _WIN32
#include <sys/mman.h>
#include <sys/user.h>
#endif

#ifdef ENABLE_JEMALLOC
#include <jemalloc/jemalloc.h>
#endif
#include <errno.h>
#include <memory>
#include <stddef.h>
#include <stdint.h>

extern "C" {
  typedef void* (*mmap_hook_type)(
            void *addr, size_t length, int prot, int flags,
            int fd, off_t offset);
  typedef int (*munmap_hook_type)(void *addr, size_t length);

#ifdef ENABLE_JEMALLOC
  extern mmap_hook_type je___mmap_hook;
  extern munmap_hook_type je___munmap_hook;
#endif
}

namespace fextl::pmr {
  static fextl::pmr::default_resource FEXDefaultResource;
  std::pmr::memory_resource* get_default_resource() {
    return &FEXDefaultResource;
  }
}

#ifndef _WIN32
namespace FEXCore::Allocator {
  MMAP_Hook mmap {::mmap};
  MUNMAP_Hook munmap {::munmap};

  uint64_t HostVASize{};

  using GLIBC_MALLOC_Hook = void*(*)(size_t, const void *caller);
  using GLIBC_REALLOC_Hook = void*(*)(void*, size_t, const void *caller);
  using GLIBC_FREE_Hook = void(*)(void*, const void *caller);

  fextl::unique_ptr<Alloc::HostAllocator> Alloc64{};

  void *FEX_mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset) {
    void *Result = Alloc64->Mmap(addr, length, prot, flags, fd, offset);
    if (Result >= (void*)-4096) {
      errno = -(uint64_t)Result;
      return (void*)-1;
    }
    return Result;
  }
  int FEX_munmap(void *addr, size_t length) {
    int Result = Alloc64->Munmap(addr, length);

    if (Result != 0) {
      errno = -Result;
      return -1;
    }
    return Result;
  }

  // This function disables glibc's ability to allocate memory through the `sbrk` interface.
  // This is run early in the lifecycle of FEX in order to make sure no 64-bit pointers can make it to the guest 32-bit application.
  //
  // How this works is that this allocates a single page at the current sbrk pointer (aligned upward to page size). This makes it
  // so that when the sbrk syscall is used to allocate more memory, it fails with an ENOMEM since it runs in to the allocated guard page.
  //
  // glibc notices the sbrk failure and falls back to regular mmap based allocations when this occurs. Ensuring that memory can still be allocated.
  void *DisableSBRKAllocations() {
    void* INVALID_PTR = reinterpret_cast<void*>(~0ULL);
    // Get the starting sbrk pointer.
    void *StartingSBRK = sbrk(0);
    if (StartingSBRK == INVALID_PTR) {
      // If sbrk is already returning invalid pointers then nothing to do here.
      return INVALID_PTR;
    }

    // Now allocate the next page after the sbrk address to ensure it can't grow.
    // In most cases at the start of `main` this will already be page aligned, which means subsequent `sbrk`
    // calls won't allocate any memory through that.
    void* AlignedBRK = reinterpret_cast<void*>(FEXCore::AlignUp(reinterpret_cast<uintptr_t>(StartingSBRK), FEXCore::Utils::FEX_PAGE_SIZE));
    void *AfterBRK = mmap(AlignedBRK, FEXCore::Utils::FEX_PAGE_SIZE, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE | MAP_NORESERVE, -1, 0);
    if (AfterBRK == INVALID_PTR) {
      // Couldn't allocate the page after the aligned brk? This should never happen.
      // FEXCore::LogMan isn't configured yet so we just need to print the message.
      fextl::fmt::print("Couldn't allocate page after SBRK.\n");
      FEX_TRAP_EXECUTION;
      return INVALID_PTR;
    }

    // Now that the page after sbrk is allocated, FEX needs to consume the remaining sbrk space.
    // This will be anywhere from [0, 4096) bytes.
    // Start allocating from 1024 byte increments just to make any steps a bit faster.
    intptr_t IncrementAmount = 1024;
    for (; IncrementAmount != 0; IncrementAmount >>= 1) {
      while (sbrk(IncrementAmount) != INVALID_PTR);
    }
    return AlignedBRK;
  }

  void ReenableSBRKAllocations(void* Ptr) {
    const void* INVALID_PTR = reinterpret_cast<void*>(~0ULL);
    if (Ptr != INVALID_PTR) {
      munmap(Ptr, FEXCore::Utils::FEX_PAGE_SIZE);
    }
  }

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  void SetupHooks() {
    Alloc64 = Alloc::OSAllocator::Create64BitAllocator();
#ifdef ENABLE_JEMALLOC
    je___mmap_hook   = FEX_mmap;
    je___munmap_hook = FEX_munmap;
#endif
    FEXCore::Allocator::mmap = FEX_mmap;
    FEXCore::Allocator::munmap = FEX_munmap;
  }

  void ClearHooks() {
#ifdef ENABLE_JEMALLOC
    je___mmap_hook   = ::mmap;
    je___munmap_hook = ::munmap;
#endif
    FEXCore::Allocator::mmap = ::mmap;
    FEXCore::Allocator::munmap = ::munmap;

    // XXX: This is currently a leak.
    // We can't work around this yet until static initializers that allocate memory are completely removed from our codebase
    // Luckily we only remove this on process shutdown, so the kernel will do the cleanup for us
    Alloc64.release();
  }
#pragma GCC diagnostic pop

  FEX_DEFAULT_VISIBILITY size_t DetermineVASize() {
    if (HostVASize) {
      return HostVASize;
    }

    static constexpr std::array<uintptr_t, 7> TLBSizes = {
      57,
      52,
      48,
      47,
      42,
      39,
      36,
    };

    for (auto Bits : TLBSizes) {
      uintptr_t Size = 1ULL << Bits;
      // Just try allocating
      // We can't actually determine VA size on ARM safely
      auto Find = [](uintptr_t Size) -> bool {
        for (int i = 0; i < 64; ++i) {
          // Try grabbing a some of the top pages of the range
          // x86 allocates some high pages in the top end
          void *Ptr = ::mmap(reinterpret_cast<void*>(Size - FEXCore::Utils::FEX_PAGE_SIZE * i), FEXCore::Utils::FEX_PAGE_SIZE, PROT_NONE, MAP_FIXED_NOREPLACE | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
          if (Ptr != (void*)~0ULL) {
            ::munmap(Ptr, FEXCore::Utils::FEX_PAGE_SIZE);
            if (Ptr == (void*)(Size - FEXCore::Utils::FEX_PAGE_SIZE * i)) {
              return true;
            }
          }
        }
        return false;
      };

      if (Find(Size)) {
        HostVASize = Bits;
        return Bits;
      }
    }

    LOGMAN_MSG_A_FMT("Couldn't determine host VA size");
    FEX_UNREACHABLE;
  }

  #define STEAL_LOG(...) // fprintf(stderr, __VA_ARGS__)

  fextl::vector<MemoryRegion> CollectMemoryGaps(uintptr_t Begin, uintptr_t End, int MapsFD) {
    fextl::vector<MemoryRegion> Regions;

    uintptr_t RegionEnd = 0;

    char Buffer[2048];
    const char *Cursor = Buffer;
    ssize_t Remaining = 0;

    bool EndOfFileReached = false;

    while (true) {
      const auto line_begin = Cursor;
      auto line_end = std::find(line_begin, Cursor + Remaining, '\n');

      // Check if the buffered data covers the entire line.
      // If not, try buffering more data.
      if (line_end == Cursor + Remaining) {
        if (EndOfFileReached) {
          // No more data to buffer. Add remaining memory and return.
          const auto MapBegin = std::max(RegionEnd, Begin);
          STEAL_LOG("[%d] EndOfFile; MapBegin: %016lX MapEnd: %016lX\n", __LINE__, MapBegin, End);
          if (End > MapBegin) {
            Regions.push_back({(void*)MapBegin, End - MapBegin});
          }

          return Regions;
        }

        // Move pending content back to the beginning, then buffer more data.
        std::copy(Cursor, Cursor + Remaining, std::begin(Buffer));
        auto PendingBytes = Remaining;
        do {
          Remaining = read(MapsFD, Buffer + PendingBytes, sizeof(Buffer) - PendingBytes);
        } while (Remaining == -1 && errno == EAGAIN);

        if (Remaining < sizeof(Buffer) - PendingBytes) {
          EndOfFileReached = true;
        }

        Remaining += PendingBytes;

        Cursor = Buffer;
        continue;
      }

      // Parse mapped region in the format "fffff7cc3000-fffff7cc4000 r--p ..."
      {
        uintptr_t RegionBegin;
        auto result = std::from_chars(Cursor, line_end, RegionBegin, 16);
        LogMan::Throw::AFmt(result.ec == std::errc{} && *result.ptr == '-', "Unexpected line format");
        Cursor = result.ptr + 1;

        // Add gap between the previous region and the current one
        const auto MapBegin = std::max(RegionEnd, Begin);
        const auto MapEnd = std::min(RegionBegin, End);
        if (MapEnd > MapBegin) {
          Regions.push_back({(void*)MapBegin, MapEnd - MapBegin});
        }

        result = std::from_chars(Cursor, line_end, RegionEnd, 16);
        LogMan::Throw::AFmt(result.ec == std::errc{} && *result.ptr == ' ', "Unexpected line format");
        Cursor = result.ptr + 1;

        STEAL_LOG("[%d] parsed line: RegionBegin=%016lX RegionEnd=%016lX\n", __LINE__, RegionBegin, RegionEnd);

        if (RegionEnd >= End) {
          // Early return if we are completely beyond the allocation space.
          return Regions;
        }
      }

      Remaining -= line_end + 1 - line_begin;
      Cursor = line_end + 1;
    }
    FEX_UNREACHABLE;
  }

  fextl::vector<MemoryRegion> StealMemoryRegion(uintptr_t Begin, uintptr_t End) {
    const uintptr_t StackLocation_u64 = reinterpret_cast<uintptr_t>(alloca(0));

    const int MapsFD = open("/proc/self/maps", O_RDONLY);
    LogMan::Throw::AFmt(MapsFD != -1, "Failed to open /proc/self/maps");

    auto Regions = CollectMemoryGaps(Begin, End, MapsFD);
    close(MapsFD);

    // If the memory bounds include the stack, blocking all memory regions will
    // limit the stack size to the current value. To allow some stack growth,
    // we don't block the memory gap directly below the stack memory but
    // instead map it as readable+writable.
    {
      auto StackRegionIt =
            std::find_if(Regions.begin(), Regions.end(),
                          [StackLocation_u64](auto& Region) {
                              return reinterpret_cast<uintptr_t>(Region.Ptr) + Region.Size > StackLocation_u64;
                          });

      // If no gap crossing the stack pointer was found but the SP is within
      // the given bounds, the stack mapping is right after the last gap.
      bool IsStackMapping = StackRegionIt != Regions.end() || StackLocation_u64 <= End;

      if (IsStackMapping && StackRegionIt != Regions.begin() &&
          reinterpret_cast<uintptr_t>(std::prev(StackRegionIt)->Ptr) + std::prev(StackRegionIt)->Size <= End) {
        // Allocate the region under the stack as READ | WRITE so the stack can still grow
        --StackRegionIt;

        auto Alloc = mmap(StackRegionIt->Ptr, StackRegionIt->Size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_NORESERVE | MAP_PRIVATE | MAP_FIXED, -1, 0);

        LogMan::Throw::AFmt(Alloc != MAP_FAILED, "mmap({:x},{:x}) failed", StackRegionIt->Ptr, StackRegionIt->Size);
        LogMan::Throw::AFmt(Alloc == StackRegionIt->Ptr, "mmap returned {} instead of {}", Alloc, fmt::ptr(StackRegionIt->Ptr));

        Regions.erase(StackRegionIt);
      }
    }

    // Block remaining memory gaps
    for (auto RegionIt = Regions.begin(); RegionIt != Regions.end(); ++RegionIt) {
      auto Alloc = mmap(RegionIt->Ptr, RegionIt->Size, PROT_NONE, MAP_ANONYMOUS | MAP_NORESERVE | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);

      LogMan::Throw::AFmt(Alloc != MAP_FAILED, "mmap({:x},{:x}) failed", RegionIt->Ptr, RegionIt->Size);
      LogMan::Throw::AFmt(Alloc == RegionIt->Ptr, "mmap returned {} instead of {}", Alloc, fmt::ptr(RegionIt->Ptr));
    }

    return Regions;
  }

  fextl::vector<MemoryRegion> Steal48BitVA() {
    size_t Bits = FEXCore::Allocator::DetermineVASize();
    if (Bits < 48) {
      return {};
    }

    uintptr_t Begin48BitVA = 0x0'8000'0000'0000ULL;
    uintptr_t End48BitVA   = 0x1'0000'0000'0000ULL;
    return StealMemoryRegion(Begin48BitVA, End48BitVA);
  }

  void ReclaimMemoryRegion(const fextl::vector<MemoryRegion> &Regions) {
    for (const auto &Region: Regions) {
      ::munmap(Region.Ptr, Region.Size);
    }
  }

  void LockBeforeFork(FEXCore::Core::InternalThreadState *Thread) {
    if (Alloc64) {
      Alloc64->LockBeforeFork(Thread);
    }
  }

  void UnlockAfterFork(FEXCore::Core::InternalThreadState *Thread, bool Child) {
    if (Alloc64) {
      Alloc64->UnlockAfterFork(Thread, Child);
    }
  }
}
#endif