libsanitizer/sanitizer_common/sanitizer_procmaps_mac.cpp

//===-- sanitizer_procmaps_mac.cpp ----------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Information about the process mappings (Mac-specific parts).
//===----------------------------------------------------------------------===//

#include "sanitizer_platform.h"
#if SANITIZER_APPLE
#include "sanitizer_common.h"
#include "sanitizer_placement_new.h"
#include "sanitizer_procmaps.h"

#include <mach-o/dyld.h>
#include <mach-o/loader.h>
#include <mach/mach.h>

// These are not available in older macOS SDKs.
#  ifndef CPU_SUBTYPE_X86_64_H
#    define CPU_SUBTYPE_X86_64_H ((cpu_subtype_t)8) /* Haswell */
#  endif
#  ifndef CPU_SUBTYPE_ARM_V7S
#    define CPU_SUBTYPE_ARM_V7S ((cpu_subtype_t)11) /* Swift */
#  endif
#  ifndef CPU_SUBTYPE_ARM_V7K
#    define CPU_SUBTYPE_ARM_V7K ((cpu_subtype_t)12)
#  endif
#  ifndef CPU_TYPE_ARM64
#    define CPU_TYPE_ARM64 (CPU_TYPE_ARM | CPU_ARCH_ABI64)
#  endif
#  ifndef CPU_SUBTYPE_ARM64E
#    define CPU_SUBTYPE_ARM64E ((cpu_subtype_t)2)
#  endif

namespace __sanitizer {

// Contains information used to iterate through sections.
struct MemoryMappedSegmentData {
  char name[kMaxSegName];
  uptr nsects;
  const char *current_load_cmd_addr;
  u32 lc_type;
  uptr base_virt_addr;
};

template <typename Section>
static void NextSectionLoad(LoadedModule *module, MemoryMappedSegmentData *data,
                            bool isWritable) {
  const Section *sc = (const Section *)data->current_load_cmd_addr;
  data->current_load_cmd_addr += sizeof(Section);

  uptr sec_start = sc->addr + data->base_virt_addr;
  uptr sec_end = sec_start + sc->size;
  module->addAddressRange(sec_start, sec_end, /*executable=*/false, isWritable,
                          sc->sectname);
}

static bool VerifyMemoryMapping(MemoryMappingLayout* mapping) {
  InternalMmapVector<LoadedModule> modules;
  modules.reserve(128);  // matches DumpProcessMap
  mapping->DumpListOfModules(&modules);

  InternalMmapVector<LoadedModule::AddressRange> segments;
  for (uptr i = 0; i < modules.size(); ++i) {
    for (auto& range : modules[i].ranges()) {
      segments.push_back(range);
    }
  }

  // Verify that none of the segments overlap:
  // 1. Sort the segments by the start address
  // 2. Check that every segment starts after the previous one ends.
  Sort(segments.data(), segments.size(),
       [](LoadedModule::AddressRange& a, LoadedModule::AddressRange& b) {
         return a.beg < b.beg;
       });

  // To avoid spam, we only print the report message once-per-process.
  static bool invalid_module_map_reported = false;
  bool well_formed = true;

  for (size_t i = 1; i < segments.size(); i++) {
    uptr cur_start = segments[i].beg;
    uptr prev_end = segments[i - 1].end;
    if (cur_start < prev_end) {
      well_formed = false;
      VReport(2, "Overlapping mappings: %s start = %p, %s end = %p\n",
              segments[i].name, (void*)cur_start, segments[i - 1].name,
              (void*)prev_end);
      if (!invalid_module_map_reported) {
        Report(
            "WARN: Invalid dyld module map detected. This is most likely a bug "
            "in the sanitizer.\n");
        Report("WARN: Backtraces may be unreliable.\n");
        invalid_module_map_reported = true;
      }
    }
  }

  for (auto& m : modules) m.clear();

  mapping->Reset();
  return well_formed;
}

void MemoryMappedSegment::AddAddressRanges(LoadedModule *module) {
  // Don't iterate over sections when the caller hasn't set up the
  // data pointer, when there are no sections, or when the segment
  // is executable. Avoid iterating over executable sections because
  // it will confuse libignore, and because the extra granularity
  // of information is not needed by any sanitizers.
  if (!data_ || !data_->nsects || IsExecutable()) {
    module->addAddressRange(start, end, IsExecutable(), IsWritable(),
                            data_ ? data_->name : nullptr);
    return;
  }

  do {
    if (data_->lc_type == LC_SEGMENT) {
      NextSectionLoad<struct section>(module, data_, IsWritable());
#ifdef MH_MAGIC_64
    } else if (data_->lc_type == LC_SEGMENT_64) {
      NextSectionLoad<struct section_64>(module, data_, IsWritable());
#endif
    }
  } while (--data_->nsects);
}

MemoryMappingLayout::MemoryMappingLayout(bool cache_enabled) {
  Reset();
  VerifyMemoryMapping(this);
}

MemoryMappingLayout::~MemoryMappingLayout() {
}

bool MemoryMappingLayout::Error() const {
  return false;
}

// More information about Mach-O headers can be found in mach-o/loader.h
// Each Mach-O image has a header (mach_header or mach_header_64) starting with
// a magic number, and a list of linker load commands directly following the
// header.
// A load command is at least two 32-bit words: the command type and the
// command size in bytes. We're interested only in segment load commands
// (LC_SEGMENT and LC_SEGMENT_64), which tell that a part of the file is mapped
// into the task's address space.
// The |vmaddr|, |vmsize| and |fileoff| fields of segment_command or
// segment_command_64 correspond to the memory address, memory size and the
// file offset of the current memory segment.
// Because these fields are taken from the images as is, one needs to add
// _dyld_get_image_vmaddr_slide() to get the actual addresses at runtime.

void MemoryMappingLayout::Reset() {
  // Count down from the top.
  // TODO(glider): as per man 3 dyld, iterating over the headers with
  // _dyld_image_count is thread-unsafe. We need to register callbacks for
  // adding and removing images which will invalidate the MemoryMappingLayout
  // state.
  data_.current_image = _dyld_image_count();
  data_.current_load_cmd_count = -1;
  data_.current_load_cmd_addr = 0;
  data_.current_magic = 0;
  data_.current_filetype = 0;
  data_.current_arch = kModuleArchUnknown;
  internal_memset(data_.current_uuid, 0, kModuleUUIDSize);
}

// The dyld load address should be unchanged throughout process execution,
// and it is expensive to compute once many libraries have been loaded,
// so cache it here and do not reset.
static mach_header *dyld_hdr = 0;
static const char kDyldPath[] = "/usr/lib/dyld";
static const int kDyldImageIdx = -1;

// static
void MemoryMappingLayout::CacheMemoryMappings() {
  // No-op on Mac for now.
}

void MemoryMappingLayout::LoadFromCache() {
  // No-op on Mac for now.
}

static bool IsDyldHdr(const mach_header *hdr) {
  return (hdr->magic == MH_MAGIC || hdr->magic == MH_MAGIC_64) &&
         hdr->filetype == MH_DYLINKER;
}

// _dyld_get_image_header() and related APIs don't report dyld itself.
// We work around this by manually recursing through the memory map
// until we hit a Mach header matching dyld instead. These recurse
// calls are expensive, but the first memory map generation occurs
// early in the process, when dyld is one of the only images loaded,
// so it will be hit after only a few iterations.  These assumptions don't hold
// on macOS 13+ anymore (dyld itself has moved into the shared cache).
static mach_header *GetDyldImageHeaderViaVMRegion() {
  vm_address_t address = 0;

  while (true) {
    vm_size_t size = 0;
    unsigned depth = 1;
    struct vm_region_submap_info_64 info;
    mach_msg_type_number_t count = VM_REGION_SUBMAP_INFO_COUNT_64;
    kern_return_t err =
        vm_region_recurse_64(mach_task_self(), &address, &size, &depth,
                             (vm_region_info_t)&info, &count);
    if (err != KERN_SUCCESS) return nullptr;

    if (size >= sizeof(mach_header) && info.protection & kProtectionRead) {
      mach_header *hdr = (mach_header *)address;
      if (IsDyldHdr(hdr)) {
        return hdr;
      }
    }
    address += size;
  }
}

extern "C" {
struct dyld_shared_cache_dylib_text_info {
  uint64_t version;  // current version 2
  // following fields all exist in version 1
  uint64_t loadAddressUnslid;
  uint64_t textSegmentSize;
  uuid_t dylibUuid;
  const char *path;  // pointer invalid at end of iterations
  // following fields all exist in version 2
  uint64_t textSegmentOffset;  // offset from start of cache
};
typedef struct dyld_shared_cache_dylib_text_info
    dyld_shared_cache_dylib_text_info;

extern bool _dyld_get_shared_cache_uuid(uuid_t uuid);
extern const void *_dyld_get_shared_cache_range(size_t *length);
extern intptr_t _dyld_get_image_slide(const struct mach_header* mh);
} // extern "C"

#ifdef __BLOCKS__
extern "C" {
extern int dyld_shared_cache_iterate_text(
    const uuid_t cacheUuid,
    void (^callback)(const dyld_shared_cache_dylib_text_info *info));
}  // extern "C"

static mach_header *GetDyldImageHeaderViaSharedCache(uuid_t uuid) {
  size_t cacheLength;
  const uptr cacheStart = (uptr)_dyld_get_shared_cache_range(&cacheLength);
  CHECK(cacheStart && cacheLength);

  __block mach_header *dyldHdr = nullptr;
  int res = dyld_shared_cache_iterate_text(
      uuid, ^(const dyld_shared_cache_dylib_text_info *info) {
        CHECK_GE(info->version, 2);
        mach_header *hdr =
            (mach_header *)(cacheStart + info->textSegmentOffset);
        if (IsDyldHdr(hdr))
          dyldHdr = hdr;
      });
  CHECK_EQ(res, 0);

  return dyldHdr;
}

#else

/* Here we implement a manual emulation of the Blocks closure and callback
   that is needed by dyld_shared_cache_iterate_text ().  In the compiler-
   generated code, the [local] names are mangled differently, but that
   should not matter to the function (since all the entities are TU-local).  */

extern "C" {
/* Some descriptions of the blocks interfaces/runtime that we need.  */
extern void *_NSConcreteStackBlock;
extern void _Block_object_assign(void *, void *, int);
extern void _Block_object_dispose(void *, int);
enum {
  BLOCK_FIELD_IS_OBJECT   =  3,  /* id, NSObject, __attribute__((NSObject)), block, ... */
  BLOCK_FIELD_IS_BLOCK    =  7,  /* a block variable */
  BLOCK_FIELD_IS_BYREF    =  8,  /* the on stack structure holding the __block variable */
  BLOCK_FIELD_IS_WEAK     = 16,  /* declared __weak, only used in byref copy helpers */
  BLOCK_BYREF_CALLER      = 128  /* called from __block (byref) copy/dispose support routines. */
};

/* 1. __block mach_header *dyldHdr; Uses this on-stack object.  */
typedef struct __block_byref_dyldHdr {
    void *__isa;
    struct __block_byref_dyldHdr *forwarding;
    int flags;   // 1<<25 iff we need copy helper;
    int size;
    mach_header *dyldHdr_cp;
} dyldHdr_type;

/* The closure, support functions and the actuall callback code.  */
/* 1. closure descriptor.  A constant instance of this will be created.  */
struct Block_descriptor_cb {
  unsigned long int reserved;     // NULL
  unsigned long int size;         // sizeof(struct Block_literal_cb)
  // optional helper functions
  void (*copy_helper)(struct Block_literal_cb *dst, struct Block_literal_cb *src);     // IFF (1<<25)
  void (*dispose_helper)(struct Block_literal_cb *src);             // IFF (1<<25)
  // required ABI.2010.3.16
  const char *signature;                         // IFF (1<<30)
  void *no_idea; // not documented in the current ABI
};

/* 2. This is the closure object.  In this case, it will be allocated on the
      stack and does not need to be moved (since the closure never escapes
      from its enclosing scope).  However, the infrastructure still provides
      support for moving it to the heap if required.  */
typedef struct Block_literal_cb {
  void *__isa;
  int flags;
  int reserved;
  void (*invoke) (Block_literal_cb*, const dyld_shared_cache_dylib_text_info *info);
  const struct Block_descriptor_cb *descriptor;
  dyldHdr_type *h_holder;
  uptr cache_start;
} CallbackBlk;

/* 3. Supporting functions to allow for the closure to be copied to the heap on
   demand.  */
static void
__block_copy_cb (struct Block_literal_cb *dst, struct Block_literal_cb *src)
{
  //_Block_byref_assign_copy(&dst->captured_i, src->captured_i);
  _Block_object_assign(&dst->h_holder, src->h_holder, BLOCK_FIELD_IS_BYREF);
}

static void
__block_dispose_cb (struct Block_literal_cb *src) {
   //_Block_byref_release(src->captured_i);
  _Block_object_dispose(src->h_holder, BLOCK_FIELD_IS_BYREF);
}

/* 4. Here is the actual code implementing the callback.  */
static void
__block_invoke_cb (struct Block_literal_cb *_block,
		   const dyld_shared_cache_dylib_text_info *info)
{
  mach_header *hdr = (mach_header *)(_block->cache_start + info->textSegmentOffset);
  if (IsDyldHdr(hdr))
    _block->h_holder->forwarding->dyldHdr_cp = hdr;
}

/* 6. The constant instance of the descriptor mentioned in 1 above.  */
static const struct Block_descriptor_cb cb_descr = {
    0, sizeof (struct Block_literal_cb), __block_copy_cb, __block_dispose_cb,
    "v16@?0r^{dyld_shared_cache_dylib_text_info=QQQ[16C]*Q}8", nullptr
};

/* Declare dyld_shared_cache_iterate_text () as taking a regular pointer to
   the closure; we cannot use the ^ syntax yet in GCC.  */
extern int dyld_shared_cache_iterate_text(const uuid_t cacheUuid, CallbackBlk*);
}  // extern "C"

/* The non-blocks version of GetDyldImageHeaderViaSharedCache ().  */
static mach_header *GetDyldImageHeaderViaSharedCache(uuid_t uuid) {
  size_t cacheLength;
  const uptr cacheStart = (uptr)_dyld_get_shared_cache_range(&cacheLength);
  CHECK(cacheStart && cacheLength);
  /* __block mach_header *dyldHdr = nullptr; */
  dyldHdr_type dyldHdr
    = { nullptr, &dyldHdr, 0, sizeof (struct __block_byref_dyldHdr), nullptr };
  /* Callback cb = ^(const dyld_shared_cache_dylib_text_info *info... */
  CallbackBlk cb
    = { _NSConcreteStackBlock, 0x42000000, 0, __block_invoke_cb,
        &cb_descr, &dyldHdr, cacheStart };
  int res = dyld_shared_cache_iterate_text ( uuid, &cb );
  CHECK_EQ(res, 0);
  return dyldHdr.forwarding->dyldHdr_cp;
}
#endif

const mach_header *get_dyld_hdr() {
  if (!dyld_hdr) {
    // On macOS 13+, dyld itself has moved into the shared cache.  Looking it up
    // via vm_region_recurse_64() causes spins/hangs/crashes.
    if (GetMacosAlignedVersion() >= MacosVersion(13, 0)) {
      uuid_t uuid;
      if (!_dyld_get_shared_cache_uuid(uuid))
        VReport(1, "Failed get the shared cache on macOS 13+\n");
      else
        dyld_hdr = GetDyldImageHeaderViaSharedCache(uuid);
      if (!dyld_hdr) {
        VReport(1,
                "Failed to lookup the dyld image header in the shared cache on "
                "macOS 13+ (or no shared cache in use).  Falling back to "
                "lookup via vm_region_recurse_64().\n");
        dyld_hdr = GetDyldImageHeaderViaVMRegion();
      }
    } else {
      dyld_hdr = GetDyldImageHeaderViaVMRegion();
    }
    CHECK(dyld_hdr);
  }

  return dyld_hdr;
}

// Next and NextSegmentLoad were inspired by base/sysinfo.cc in
// Google Perftools, https://github.com/gperftools/gperftools.

// NextSegmentLoad scans the current image for the next segment load command
// and returns the start and end addresses and file offset of the corresponding
// segment.
// Note that the segment addresses are not necessarily sorted.
template <u32 kLCSegment, typename SegmentCommand>
static bool NextSegmentLoad(MemoryMappedSegment *segment,
                            MemoryMappedSegmentData *seg_data,
                            MemoryMappingLayoutData *layout_data) {
  const char *lc = layout_data->current_load_cmd_addr;

  layout_data->current_load_cmd_addr += ((const load_command *)lc)->cmdsize;
  layout_data->current_load_cmd_count--;
  if (((const load_command *)lc)->cmd == kLCSegment) {
    const SegmentCommand* sc = (const SegmentCommand *)lc;
    if (internal_strcmp(sc->segname, "__LINKEDIT") == 0) {
      // The LINKEDIT sections are for internal linker use, and may alias
      // with the LINKEDIT section for other modules. (If we included them,
      // our memory map would contain overlappping sections.)
      return false;
    }

    uptr base_virt_addr;
    if (layout_data->current_image == kDyldImageIdx)
      base_virt_addr = (uptr)_dyld_get_image_slide(get_dyld_hdr());
    else
      base_virt_addr =
          (uptr)_dyld_get_image_vmaddr_slide(layout_data->current_image);

    segment->start = sc->vmaddr + base_virt_addr;
    segment->end = segment->start + sc->vmsize;
    // Most callers don't need section information, so only fill this struct
    // when required.
    if (seg_data) {
      seg_data->nsects = sc->nsects;
      seg_data->current_load_cmd_addr =
          (const char *)lc + sizeof(SegmentCommand);
      seg_data->lc_type = kLCSegment;
      seg_data->base_virt_addr = base_virt_addr;
      internal_strncpy(seg_data->name, sc->segname,
                       ARRAY_SIZE(seg_data->name));
      seg_data->name[ARRAY_SIZE(seg_data->name) - 1] = 0;
    }

    // Return the initial protection.
    segment->protection = sc->initprot;
    segment->offset = (layout_data->current_filetype ==
                       /*MH_EXECUTE*/ 0x2)
                          ? sc->vmaddr
                          : sc->fileoff;
    if (segment->filename) {
      const char *src = (layout_data->current_image == kDyldImageIdx)
                            ? kDyldPath
                            : _dyld_get_image_name(layout_data->current_image);
      internal_strncpy(segment->filename, src, segment->filename_size);
      segment->filename[segment->filename_size - 1] = 0;
    }
    segment->arch = layout_data->current_arch;
    internal_memcpy(segment->uuid, layout_data->current_uuid, kModuleUUIDSize);
    return true;
  }
  return false;
}

ModuleArch ModuleArchFromCpuType(cpu_type_t cputype, cpu_subtype_t cpusubtype) {
  cpusubtype = cpusubtype & ~CPU_SUBTYPE_MASK;
  switch (cputype) {
    case CPU_TYPE_I386:
      return kModuleArchI386;
    case CPU_TYPE_X86_64:
      if (cpusubtype == CPU_SUBTYPE_X86_64_ALL)
        return kModuleArchX86_64;
      if (cpusubtype == CPU_SUBTYPE_X86_64_H)
        return kModuleArchX86_64H;
      CHECK(0 && "Invalid subtype of x86_64");
      return kModuleArchUnknown;
    case CPU_TYPE_ARM:
      if (cpusubtype == CPU_SUBTYPE_ARM_V6)
        return kModuleArchARMV6;
      if (cpusubtype == CPU_SUBTYPE_ARM_V7)
        return kModuleArchARMV7;
      if (cpusubtype == CPU_SUBTYPE_ARM_V7S)
        return kModuleArchARMV7S;
      if (cpusubtype == CPU_SUBTYPE_ARM_V7K)
        return kModuleArchARMV7K;
      CHECK(0 && "Invalid subtype of ARM");
      return kModuleArchUnknown;
    case CPU_TYPE_ARM64:
      if (cpusubtype == CPU_SUBTYPE_ARM64E)
        return kModuleArchARM64E;
      return kModuleArchARM64;
    default:
      CHECK(0 && "Invalid CPU type");
      return kModuleArchUnknown;
  }
}

static const load_command *NextCommand(const load_command *lc) {
  return (const load_command *)((const char *)lc + lc->cmdsize);
}

#  ifdef MH_MAGIC_64
static constexpr size_t header_size = sizeof(mach_header_64);
#  else
static constexpr size_t header_size = sizeof(mach_header);
#  endif

static void FindUUID(const load_command *first_lc, const mach_header *hdr,
                     u8 *uuid_output) {
  uint32_t curcmd = 0;
  for (const load_command *lc = first_lc; curcmd < hdr->ncmds;
       curcmd++, lc = NextCommand(lc)) {
    CHECK_LT((const char *)lc,
             (const char *)hdr + header_size + hdr->sizeofcmds);

    if (lc->cmd != LC_UUID)
      continue;

    const uuid_command *uuid_lc = (const uuid_command *)lc;
    const uint8_t *uuid = &uuid_lc->uuid[0];
    internal_memcpy(uuid_output, uuid, kModuleUUIDSize);
    return;
  }
}

static bool IsModuleInstrumented(const load_command *first_lc,
                                 const mach_header *hdr) {
  uint32_t curcmd = 0;
  for (const load_command *lc = first_lc; curcmd < hdr->ncmds;
       curcmd++, lc = NextCommand(lc)) {
    CHECK_LT((const char *)lc,
             (const char *)hdr + header_size + hdr->sizeofcmds);

    if (lc->cmd != LC_LOAD_DYLIB)
      continue;

    const dylib_command *dylib_lc = (const dylib_command *)lc;
    uint32_t dylib_name_offset = dylib_lc->dylib.name.offset;
    const char *dylib_name = ((const char *)dylib_lc) + dylib_name_offset;
    dylib_name = StripModuleName(dylib_name);
    if (dylib_name != 0 && (internal_strstr(dylib_name, "libclang_rt."))) {
      return true;
    }
  }
  return false;
}

const ImageHeader *MemoryMappingLayout::CurrentImageHeader() {
  const mach_header *hdr = (data_.current_image == kDyldImageIdx)
                                ? get_dyld_hdr()
                                : _dyld_get_image_header(data_.current_image);
  return (const ImageHeader *)hdr;
}

bool MemoryMappingLayout::Next(MemoryMappedSegment *segment) {
  for (; data_.current_image >= kDyldImageIdx; data_.current_image--) {
    const mach_header *hdr = (const mach_header *)CurrentImageHeader();
    if (!hdr) continue;
    if (data_.current_load_cmd_count < 0) {
      // Set up for this image;
      data_.current_load_cmd_count = hdr->ncmds;
      data_.current_magic = hdr->magic;
      data_.current_filetype = hdr->filetype;
      data_.current_arch = ModuleArchFromCpuType(hdr->cputype, hdr->cpusubtype);
      switch (data_.current_magic) {
#ifdef MH_MAGIC_64
        case MH_MAGIC_64: {
          data_.current_load_cmd_addr =
              (const char *)hdr + sizeof(mach_header_64);
          break;
        }
#endif
        case MH_MAGIC: {
          data_.current_load_cmd_addr = (const char *)hdr + sizeof(mach_header);
          break;
        }
        default: {
          continue;
        }
      }
      FindUUID((const load_command *)data_.current_load_cmd_addr, hdr,
               data_.current_uuid);
      data_.current_instrumented = IsModuleInstrumented(
          (const load_command *)data_.current_load_cmd_addr, hdr);
    }

    while (data_.current_load_cmd_count > 0) {
      switch (data_.current_magic) {
        // data_.current_magic may be only one of MH_MAGIC, MH_MAGIC_64.
#ifdef MH_MAGIC_64
        case MH_MAGIC_64: {
          if (NextSegmentLoad<LC_SEGMENT_64, struct segment_command_64>(
                  segment, segment->data_, &data_))
            return true;
          break;
        }
#endif
        case MH_MAGIC: {
          if (NextSegmentLoad<LC_SEGMENT, struct segment_command>(
                  segment, segment->data_, &data_))
            return true;
          break;
        }
      }
    }
    // If we get here, no more load_cmd's in this image talk about
    // segments.  Go on to the next image.
    data_.current_load_cmd_count = -1; // This will trigger loading next image
  }
  return false;
}

void MemoryMappingLayout::DumpListOfModules(
    InternalMmapVectorNoCtor<LoadedModule> *modules) {
  Reset();
  InternalMmapVector<char> module_name(kMaxPathLength);
  MemoryMappedSegment segment(module_name.data(), module_name.size());
  MemoryMappedSegmentData data;
  segment.data_ = &data;
  while (Next(&segment)) {
    // skip the __PAGEZERO segment, its vmsize is 0
    if (segment.filename[0] == '\0' || (segment.start == segment.end))
      continue;
    LoadedModule *cur_module = nullptr;
    if (!modules->empty() &&
        0 == internal_strcmp(segment.filename, modules->back().full_name())) {
      cur_module = &modules->back();
    } else {
      modules->push_back(LoadedModule());
      cur_module = &modules->back();
      cur_module->set(segment.filename, segment.start, segment.arch,
                      segment.uuid, data_.current_instrumented);
    }
    segment.AddAddressRanges(cur_module);
  }
}

}  // namespace __sanitizer

#endif  // SANITIZER_APPLE