diff --git a/.github/pyinstaller/pyinstaller.spec b/.github/pyinstaller/pyinstaller.spec
index b8967751..7e7ae207 100644
--- a/.github/pyinstaller/pyinstaller.spec
+++ b/.github/pyinstaller/pyinstaller.spec
@@ -33,6 +33,7 @@ a = Analysis(
         # this gets invoked from the directory of the spec file,
         # i.e. ./.github/pyinstaller
         ('../../rules', 'rules'),
+        ('../../sigs', 'sigs'),
 
         # capa.render.default uses tabulate that depends on wcwidth.
         # it seems wcwidth uses a json file `version.json`
@@ -108,5 +109,4 @@ exe = EXE(pyz,
 #               a.datas,
 #               strip=None,
 #               upx=True,
-#               name='capa-dat')
-
+#               name='capa-dat')
\ No newline at end of file
diff --git a/capa/features/extractors/__init__.py b/capa/features/extractors/__init__.py
index 2cdbd4af..1faea42d 100644
--- a/capa/features/extractors/__init__.py
+++ b/capa/features/extractors/__init__.py
@@ -76,6 +76,41 @@ class FeatureExtractor(object):
         """
         raise NotImplemented
 
+    def is_library_function(self, va):
+        """
+        is the given address a library function?
+        the backend may implement its own function matching algorithm, or none at all.
+        we accept a VA here, rather than function object, to handle addresses identified in instructions.
+
+        this information is used to:
+          - filter out matches in library functions (by default), and
+          - recognize when to fetch symbol names for called (non-API) functions
+
+        args:
+          va (int): the virtual address of a function.
+
+        returns:
+          bool: True if the given address is the start of a library function.
+        """
+        return False
+
+    def get_function_name(self, va):
+        """
+        fetch any recognized name for the given address.
+        this is only guaranteed to return a value when the given function is a recognized library function.
+        we accept a VA here, rather than function object, to handle addresses identified in instructions.
+
+        args:
+          va (int): the virtual address of a function.
+
+        returns:
+          str: the function name
+
+        raises:
+          KeyError: when the given function does not have a name.
+        """
+        raise KeyError(va)
+
     @abc.abstractmethod
     def extract_function_features(self, f):
         """
diff --git a/capa/features/extractors/ida/__init__.py b/capa/features/extractors/ida/__init__.py
index 689975b9..a089c9ae 100644
--- a/capa/features/extractors/ida/__init__.py
+++ b/capa/features/extractors/ida/__init__.py
@@ -6,9 +6,6 @@
 #  is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and limitations under the License.
 
-import sys
-import types
-
 import idaapi
 
 import capa.features.extractors.ida.file
@@ -18,24 +15,43 @@ import capa.features.extractors.ida.basicblock
 from capa.features.extractors import FeatureExtractor
 
 
-def get_ea(self):
-    """ """
-    if isinstance(self, (idaapi.BasicBlock, idaapi.func_t)):
+class FunctionHandle:
+    """this acts like an idaapi.func_t but with __int__()"""
+
+    def __init__(self, inner):
+        self._inner = inner
+
+    def __int__(self):
         return self.start_ea
-    if isinstance(self, idaapi.insn_t):
+
+    def __getattr__(self, name):
+        return getattr(self._inner, name)
+
+
+class BasicBlockHandle:
+    """this acts like an idaapi.BasicBlock but with __int__()"""
+
+    def __init__(self, inner):
+        self._inner = inner
+
+    def __int__(self):
+        return self.start_ea
+
+    def __getattr__(self, name):
+        return getattr(self._inner, name)
+
+
+class InstructionHandle:
+    """this acts like an idaapi.insn_t but with __int__()"""
+
+    def __init__(self, inner):
+        self._inner = inner
+
+    def __int__(self):
         return self.ea
-    raise TypeError
 
-
-def add_ea_int_cast(o):
-    """
-    dynamically add a cast-to-int (`__int__`) method to the given object
-    that returns the value of the `.ea` property.
-    this bit of skullduggery lets use cast viv-utils objects as ints.
-    the correct way of doing this is to update viv-utils (or subclass the objects here).
-    """
-    setattr(o, "__int__", types.MethodType(get_ea, o))
-    return o
+    def __getattr__(self, name):
+        return getattr(self._inner, name)
 
 
 class IdaFeatureExtractor(FeatureExtractor):
@@ -59,21 +75,23 @@ class IdaFeatureExtractor(FeatureExtractor):
         # ignore library functions and thunk functions as identified by IDA
         for f in ida_helpers.get_functions(skip_thunks=True, skip_libs=True):
             setattr(f, "ctx", ctx)
-            yield add_ea_int_cast(f)
+            yield FunctionHandle(f)
 
     @staticmethod
     def get_function(ea):
         f = idaapi.get_func(ea)
         setattr(f, "ctx", {})
-        return add_ea_int_cast(f)
+        return FunctionHandle(f)
 
     def extract_function_features(self, f):
         for (feature, ea) in capa.features.extractors.ida.function.extract_features(f):
             yield feature, ea
 
     def get_basic_blocks(self, f):
-        for bb in capa.features.extractors.ida.helpers.get_function_blocks(f):
-            yield add_ea_int_cast(bb)
+        import capa.features.extractors.ida.helpers as ida_helpers
+
+        for bb in ida_helpers.get_function_blocks(f):
+            yield BasicBlockHandle(bb)
 
     def extract_basic_block_features(self, f, bb):
         for (feature, ea) in capa.features.extractors.ida.basicblock.extract_features(f, bb):
@@ -83,7 +101,7 @@ class IdaFeatureExtractor(FeatureExtractor):
         import capa.features.extractors.ida.helpers as ida_helpers
 
         for insn in ida_helpers.get_instructions_in_range(bb.start_ea, bb.end_ea):
-            yield add_ea_int_cast(insn)
+            yield InstructionHandle(insn)
 
     def extract_insn_features(self, f, bb, insn):
         for (feature, ea) in capa.features.extractors.ida.insn.extract_features(f, bb, insn):
diff --git a/capa/features/extractors/viv/__init__.py b/capa/features/extractors/viv/__init__.py
index 47581236..c54ee0be 100644
--- a/capa/features/extractors/viv/__init__.py
+++ b/capa/features/extractors/viv/__init__.py
@@ -5,10 +5,10 @@
 # Unless required by applicable law or agreed to in writing, software distributed under the License
 #  is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and limitations under the License.
-
-import types
+import logging
 
 import viv_utils
+import viv_utils.flirt
 
 import capa.features.extractors
 import capa.features.extractors.viv.file
@@ -18,28 +18,20 @@ import capa.features.extractors.viv.basicblock
 from capa.features.extractors import FeatureExtractor
 
 __all__ = ["file", "function", "basicblock", "insn"]
+logger = logging.getLogger(__name__)
 
 
-def get_va(self):
-    try:
-        # vivisect type
+class InstructionHandle:
+    """this acts like a vivisect.Opcode but with an __int__() method"""
+
+    def __init__(self, inner):
+        self._inner = inner
+
+    def __int__(self):
         return self.va
-    except AttributeError:
-        pass
 
-    raise TypeError()
-
-
-def add_va_int_cast(o):
-    """
-    dynamically add a cast-to-int (`__int__`) method to the given object
-    that returns the value of the `.va` property.
-
-    this bit of skullduggery lets use cast viv-utils objects as ints.
-    the correct way of doing this is to update viv-utils (or subclass the objects here).
-    """
-    setattr(o, "__int__", types.MethodType(get_va, o))
-    return o
+    def __getattr__(self, name):
+        return getattr(self._inner, name)
 
 
 class VivisectFeatureExtractor(FeatureExtractor):
@@ -58,15 +50,14 @@ class VivisectFeatureExtractor(FeatureExtractor):
 
     def get_functions(self):
         for va in sorted(self.vw.getFunctions()):
-            yield add_va_int_cast(viv_utils.Function(self.vw, va))
+            yield viv_utils.Function(self.vw, va)
 
     def extract_function_features(self, f):
         for feature, va in capa.features.extractors.viv.function.extract_features(f):
             yield feature, va
 
     def get_basic_blocks(self, f):
-        for bb in f.basic_blocks:
-            yield add_va_int_cast(bb)
+        return f.basic_blocks
 
     def extract_basic_block_features(self, f, bb):
         for feature, va in capa.features.extractors.viv.basicblock.extract_features(f, bb):
@@ -74,8 +65,14 @@ class VivisectFeatureExtractor(FeatureExtractor):
 
     def get_instructions(self, f, bb):
         for insn in bb.instructions:
-            yield add_va_int_cast(insn)
+            yield InstructionHandle(insn)
 
     def extract_insn_features(self, f, bb, insn):
         for feature, va in capa.features.extractors.viv.insn.extract_features(f, bb, insn):
             yield feature, va
+
+    def is_library_function(self, va):
+        return viv_utils.flirt.is_library_function(self.vw, va)
+
+    def get_function_name(self, va):
+        return viv_utils.get_function_name(self.vw, va)
diff --git a/capa/features/extractors/viv/insn.py b/capa/features/extractors/viv/insn.py
index 42deee51..f6c9273c 100644
--- a/capa/features/extractors/viv/insn.py
+++ b/capa/features/extractors/viv/insn.py
@@ -5,10 +5,14 @@
 # Unless required by applicable law or agreed to in writing, software distributed under the License
 #  is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and limitations under the License.
+import sys
 
+import viv_utils
 import envi.memory
+import viv_utils.flirt
 import envi.archs.i386.disasm
 
+import capa.features.extractors.viv
 import capa.features.extractors.helpers
 import capa.features.extractors.viv.helpers
 from capa.features import (
@@ -74,7 +78,6 @@ def extract_insn_api_features(f, bb, insn):
     # example:
     #
     #    call dword [0x00473038]
-
     if insn.mnem not in ("call", "jmp"):
         return
 
@@ -96,7 +99,7 @@ def extract_insn_api_features(f, bb, insn):
     # call via thunk on x86,
     # see 9324d1a8ae37a36ae560c37448c9705a at 0x407985
     #
-    # this is also how calls to internal functions may be decoded on x64.
+    # this is also how calls to internal functions may be decoded on x32 and x64.
     # see Lab21-01.exe_:0x140001178
     #
     # follow chained thunks, e.g. in 82bf6347acf15e5d883715dc289d8a2b at 0x14005E0FF in
@@ -111,6 +114,11 @@ def extract_insn_api_features(f, bb, insn):
         if not target:
             return
 
+        if viv_utils.flirt.is_library_function(f.vw, target):
+            name = viv_utils.get_function_name(f.vw, target)
+            yield API(name), insn.va
+            return
+
         for _ in range(THUNK_CHAIN_DEPTH_DELTA):
             if target in imports:
                 dll, symbol = imports[target]
diff --git a/capa/features/freeze.py b/capa/features/freeze.py
index 53c69f1a..68e93563 100644
--- a/capa/features/freeze.py
+++ b/capa/features/freeze.py
@@ -122,7 +122,7 @@ def dumps(extractor):
                 )
 
             for insnva, insn in sorted(
-                [(insn.__int__(), insn) for insn in extractor.get_instructions(f, bb)], key=lambda p: p[0]
+                [(int(insn), insn) for insn in extractor.get_instructions(f, bb)], key=lambda p: p[0]
             ):
                 ret["functions"][hex(f)][hex(bb)].append(hex(insnva))
 
@@ -248,43 +248,13 @@ def main(argv=None):
     if argv is None:
         argv = sys.argv[1:]
 
-    formats = [
-        ("auto", "(default) detect file type automatically"),
-        ("pe", "Windows PE file"),
-        ("sc32", "32-bit shellcode"),
-        ("sc64", "64-bit shellcode"),
-    ]
-    format_help = ", ".join(["%s: %s" % (f[0], f[1]) for f in formats])
-
     parser = argparse.ArgumentParser(description="save capa features to a file")
-    parser.add_argument("sample", type=str, help="Path to sample to analyze")
+    capa.main.install_common_args(parser, {"sample", "format", "backend", "signatures"})
     parser.add_argument("output", type=str, help="Path to output file")
-    parser.add_argument("-v", "--verbose", action="store_true", help="Enable verbose output")
-    parser.add_argument("-q", "--quiet", action="store_true", help="Disable all output but errors")
-    parser.add_argument(
-        "-f", "--format", choices=[f[0] for f in formats], default="auto", help="Select sample format, %s" % format_help
-    )
-    parser.add_argument(
-        "-b",
-        "--backend",
-        type=str,
-        help="select the backend to use",
-        choices=(capa.main.BACKEND_VIV, capa.main.BACKEND_SMDA),
-        default=capa.main.BACKEND_VIV,
-    )
     args = parser.parse_args(args=argv)
+    capa.main.handle_common_args(args)
 
-    if args.quiet:
-        logging.basicConfig(level=logging.ERROR)
-        logging.getLogger().setLevel(logging.ERROR)
-    elif args.verbose:
-        logging.basicConfig(level=logging.DEBUG)
-        logging.getLogger().setLevel(logging.DEBUG)
-    else:
-        logging.basicConfig(level=logging.INFO)
-        logging.getLogger().setLevel(logging.INFO)
-
-    extractor = capa.main.get_extractor(args.sample, args.format, args.backend)
+    extractor = capa.main.get_extractor(args.sample, args.format, args.backend, sigpaths=args.signatures)
     with open(args.output, "wb") as f:
         f.write(dump(extractor))
 
diff --git a/capa/helpers.py b/capa/helpers.py
index f5e1e5b0..9e799a44 100644
--- a/capa/helpers.py
+++ b/capa/helpers.py
@@ -12,18 +12,7 @@ _hex = hex
 
 
 def hex(i):
-    return _hex(oint(i))
-
-
-def oint(i):
-    # there seems to be some trouble with using `int(viv_utils.Function)`
-    # with the black magic we do with binding the `__int__()` routine.
-    # i haven't had a chance to debug this yet (and i have no hotel wifi).
-    # so in the meantime, detect this, and call the method directly.
-    try:
-        return int(i)
-    except TypeError:
-        return i.__int__()
+    return _hex(int(i))
 
 
 def get_file_taste(sample_path):
diff --git a/capa/ida/plugin/form.py b/capa/ida/plugin/form.py
index f16f5abe..3c71716e 100644
--- a/capa/ida/plugin/form.py
+++ b/capa/ida/plugin/form.py
@@ -78,7 +78,7 @@ def find_func_features(f, extractor):
                 _bb_features[feature].add(ea)
                 func_features[feature].add(ea)
 
-        bb_features[capa.helpers.oint(bb)] = _bb_features
+        bb_features[int(bb)] = _bb_features
 
     return func_features, bb_features
 
@@ -100,7 +100,7 @@ def find_func_matches(f, ruleset, func_features, bb_features):
                 func_features[capa.features.MatchedRule(name)].add(ea)
 
     # find rule matches for function, function features include rule matches for basic blocks
-    _, matches = capa.engine.match(ruleset.function_rules, func_features, capa.helpers.oint(f))
+    _, matches = capa.engine.match(ruleset.function_rules, func_features, int(f))
     for (name, res) in matches.items():
         func_matches[name].extend(res)
 
diff --git a/capa/main.py b/capa/main.py
index 82f6f4a6..61a0eaa3 100644
--- a/capa/main.py
+++ b/capa/main.py
@@ -10,16 +10,20 @@ See the License for the specific language governing permissions and limitations
 """
 import os
 import sys
+import gzip
+import time
 import hashlib
 import logging
 import os.path
 import argparse
 import datetime
 import textwrap
+import contextlib
 import collections
 
 import halo
 import tqdm
+import flirt
 import colorama
 
 import capa.rules
@@ -29,7 +33,7 @@ import capa.version
 import capa.features
 import capa.features.freeze
 import capa.features.extractors
-from capa.helpers import oint, get_file_taste
+from capa.helpers import get_file_taste
 
 RULES_PATH_DEFAULT_STRING = "(embedded rules)"
 SUPPORTED_FILE_MAGIC = set([b"MZ"])
@@ -42,6 +46,14 @@ EXTENSIONS_SHELLCODE_64 = ("sc64", "raw64")
 logger = logging.getLogger("capa")
 
 
+@contextlib.contextmanager
+def timing(msg):
+    t0 = time.time()
+    yield
+    t1 = time.time()
+    logger.debug("perf: %s: %0.2fs", msg, t1 - t0)
+
+
 def set_vivisect_log_level(level):
     logging.getLogger("vivisect").setLevel(level)
     logging.getLogger("vivisect.base").setLevel(level)
@@ -76,14 +88,14 @@ def find_function_capabilities(ruleset, extractor, f):
                 bb_features[feature].add(va)
                 function_features[feature].add(va)
 
-        _, matches = capa.engine.match(ruleset.basic_block_rules, bb_features, oint(bb))
+        _, matches = capa.engine.match(ruleset.basic_block_rules, bb_features, int(bb))
 
         for rule_name, res in matches.items():
             bb_matches[rule_name].extend(res)
             for va, _ in res:
                 function_features[capa.features.MatchedRule(rule_name)].add(va)
 
-    _, function_matches = capa.engine.match(ruleset.function_rules, function_features, oint(f))
+    _, function_matches = capa.engine.match(ruleset.function_rules, function_features, int(f))
     return function_matches, bb_matches, len(function_features)
 
 
@@ -125,10 +137,19 @@ def find_capabilities(ruleset, extractor, disable_progress=None):
         # to disable progress completely
         pbar = lambda s, *args, **kwargs: s
 
-    for f in pbar(list(extractor.get_functions()), desc="matching", unit=" functions"):
+    functions = list(extractor.get_functions())
+
+    for f in pbar(functions, desc="matching", unit=" functions"):
+        function_address = int(f)
+
+        if extractor.is_library_function(function_address):
+            function_name = extractor.get_function_name(function_address)
+            logger.debug("skipping library function 0x%x (%s)", function_address, function_name)
+            continue
+
         function_matches, bb_matches, feature_count = find_function_capabilities(ruleset, extractor, f)
-        meta["feature_counts"]["functions"][f.__int__()] = feature_count
-        logger.debug("analyzed function 0x%x and extracted %d features", f.__int__(), feature_count)
+        meta["feature_counts"]["functions"][function_address] = feature_count
+        logger.debug("analyzed function 0x%x and extracted %d features", function_address, feature_count)
 
         for rule_name, res in function_matches.items():
             all_function_matches[rule_name].extend(res)
@@ -136,7 +157,7 @@ def find_capabilities(ruleset, extractor, disable_progress=None):
             all_bb_matches[rule_name].extend(res)
 
     # mapping from matched rule feature to set of addresses at which it matched.
-    # schema: Dic[MatchedRule: Set[int]
+    # schema: Dict[MatchedRule: Set[int]
     function_features = {
         capa.features.MatchedRule(rule_name): set(map(lambda p: p[0], results))
         for rule_name, results in all_function_matches.items()
@@ -229,26 +250,31 @@ def is_supported_file_type(sample):
 SHELLCODE_BASE = 0x690000
 
 
-def get_shellcode_vw(sample, arch="auto", should_save=True):
+def get_shellcode_vw(sample, arch="auto"):
     """
-    Return shellcode workspace using explicit arch or via auto detect
+    Return shellcode workspace using explicit arch or via auto detect.
+    The workspace is *not* analyzed nor saved. Its up to the caller to do this.
+    Then, they can register FLIRT analyzers or decide not to write to disk.
     """
     import viv_utils
 
     with open(sample, "rb") as f:
         sample_bytes = f.read()
+
     if arch == "auto":
         # choose arch with most functions, idea by Jay G.
         vw_cands = []
         for arch in ["i386", "amd64"]:
             vw_cands.append(
-                viv_utils.getShellcodeWorkspace(sample_bytes, arch, base=SHELLCODE_BASE, should_save=should_save)
+                viv_utils.getShellcodeWorkspace(
+                    sample_bytes, arch, base=SHELLCODE_BASE, analyze=False, should_save=False
+                )
             )
         if not vw_cands:
             raise ValueError("could not generate vivisect workspace")
         vw = max(vw_cands, key=lambda vw: len(vw.getFunctions()))
     else:
-        vw = viv_utils.getShellcodeWorkspace(sample_bytes, arch, base=SHELLCODE_BASE, should_save=should_save)
+        vw = viv_utils.getShellcodeWorkspace(sample_bytes, arch, base=SHELLCODE_BASE, analyze=False, should_save=False)
 
     vw.setMeta("StorageName", "%s.viv" % sample)
 
@@ -266,26 +292,114 @@ def get_meta_str(vw):
     return "%s, number of functions: %d" % (", ".join(meta), len(vw.getFunctions()))
 
 
+def load_flirt_signature(path):
+
+    if path.endswith(".sig"):
+        with open(path, "rb") as f:
+            with timing("flirt: parsing .sig: " + path):
+                sigs = flirt.parse_sig(f.read())
+
+    elif path.endswith(".pat"):
+        with open(path, "rb") as f:
+            with timing("flirt: parsing .pat: " + path):
+                sigs = flirt.parse_pat(f.read().decode("utf-8").replace("\r\n", "\n"))
+
+    elif path.endswith(".pat.gz"):
+        with gzip.open(path, "rb") as f:
+            with timing("flirt: parsing .pat.gz: " + path):
+                sigs = flirt.parse_pat(f.read().decode("utf-8").replace("\r\n", "\n"))
+
+    else:
+        raise ValueError("unexpect signature file extension: " + path)
+
+    return sigs
+
+
+def register_flirt_signature_analyzers(vw, sigpaths):
+    """
+    args:
+      vw (vivisect.VivWorkspace):
+      sigpaths (List[str]): file system paths of .sig/.pat files
+    """
+    import viv_utils.flirt
+
+    for sigpath in sigpaths:
+        sigs = load_flirt_signature(sigpath)
+
+        logger.debug("flirt: sig count: %d", len(sigs))
+
+        with timing("flirt: compiling sigs"):
+            matcher = flirt.compile(sigs)
+
+        analyzer = viv_utils.flirt.FlirtFunctionAnalyzer(matcher, sigpath)
+        logger.debug("registering viv function analyzer: %s", repr(analyzer))
+        viv_utils.flirt.addFlirtFunctionAnalyzer(vw, analyzer)
+
+
+def get_default_signatures():
+    if hasattr(sys, "frozen") and hasattr(sys, "_MEIPASS"):
+        logger.debug("detected running under PyInstaller")
+        sigs_path = os.path.join(sys._MEIPASS, "sigs")
+        logger.debug("default signatures path (PyInstaller method): %s", sigs_path)
+    else:
+        logger.debug("detected running from source")
+        sigs_path = os.path.join(os.path.dirname(__file__), "..", "sigs")
+        logger.debug("default signatures path (source method): %s", sigs_path)
+
+    ret = []
+    for root, dirs, files in os.walk(sigs_path):
+        for file in files:
+            if not (file.endswith(".pat") or file.endswith(".pat.gz") or file.endswith(".sig")):
+                continue
+
+            ret.append(os.path.join(root, file))
+
+    return ret
+
+
 class UnsupportedFormatError(ValueError):
     pass
 
 
-def get_workspace(path, format, should_save=True):
+def get_workspace(path, format, sigpaths):
+    """
+    load the program at the given path into a vivisect workspace using the given format.
+    also apply the given FLIRT signatures.
+
+    supported formats:
+      - pe
+      - sc32
+      - sc64
+      - auto
+
+    this creates and analyzes the workspace; however, it does *not* save the workspace.
+    this is the responsibility of the caller.
+    """
+
+    # lazy import enables us to not require viv if user wants SMDA, for example.
     import viv_utils
 
     logger.debug("generating vivisect workspace for: %s", path)
     if format == "auto":
         if not is_supported_file_type(path):
             raise UnsupportedFormatError()
-        vw = viv_utils.getWorkspace(path, should_save=should_save)
+
+        # don't analyze, so that we can add our Flirt function analyzer first.
+        vw = viv_utils.getWorkspace(path, analyze=False, should_save=False)
     elif format == "pe":
-        vw = viv_utils.getWorkspace(path, should_save=should_save)
+        vw = viv_utils.getWorkspace(path, analyze=False, should_save=False)
     elif format == "sc32":
-        vw = get_shellcode_vw(path, arch="i386", should_save=should_save)
+        # these are not analyzed nor saved.
+        vw = get_shellcode_vw(path, arch="i386")
     elif format == "sc64":
-        vw = get_shellcode_vw(path, arch="amd64", should_save=should_save)
+        vw = get_shellcode_vw(path, arch="amd64")
     else:
         raise ValueError("unexpected format: " + format)
+
+    register_flirt_signature_analyzers(vw, sigpaths)
+
+    vw.analyze()
+
     logger.debug("%s", get_meta_str(vw))
     return vw
 
@@ -294,7 +408,7 @@ class UnsupportedRuntimeError(RuntimeError):
     pass
 
 
-def get_extractor(path, format, backend, disable_progress=False):
+def get_extractor(path, format, backend, sigpaths, disable_progress=False):
     """
     raises:
       UnsupportedFormatError:
@@ -321,7 +435,7 @@ def get_extractor(path, format, backend, disable_progress=False):
                 format = "sc32"
             elif format == "auto" and path.endswith(EXTENSIONS_SHELLCODE_64):
                 format = "sc64"
-            vw = get_workspace(path, format, should_save=False)
+            vw = get_workspace(path, format, sigpaths)
 
             try:
                 vw.saveWorkspace()
@@ -524,6 +638,18 @@ def install_common_args(parser, wanted=None):
             help="path to rule file or directory, use embedded rules by default",
         )
 
+    if "signatures" in wanted:
+        parser.add_argument(
+            "--signature",
+            action="append",
+            dest="signatures",
+            type=str,
+            # with action=append, users can specify futher signatures but not override whats found in $capa/sigs/.
+            # seems reasonable for now. this is an easy way to register the default signature set.
+            default=get_default_signatures(),
+            help="use the given signatures to identify library functions, file system paths to .sig/.pat files.",
+        )
+
     if "tag" in wanted:
         parser.add_argument("-t", "--tag", type=str, help="filter on rule meta field values")
 
@@ -609,7 +735,7 @@ def main(argv=None):
     parser = argparse.ArgumentParser(
         description=desc, epilog=epilog, formatter_class=argparse.RawDescriptionHelpFormatter
     )
-    install_common_args(parser, {"sample", "format", "backend", "rules", "tag"})
+    install_common_args(parser, {"sample", "format", "backend", "signatures", "rules", "tag"})
     parser.add_argument("-j", "--json", action="store_true", help="emit JSON instead of text")
     args = parser.parse_args(args=argv)
     handle_common_args(args)
@@ -678,7 +804,7 @@ def main(argv=None):
     else:
         format = args.format
         try:
-            extractor = get_extractor(args.sample, format, args.backend, disable_progress=args.quiet)
+            extractor = get_extractor(args.sample, format, args.backend, args.signatures, disable_progress=args.quiet)
         except UnsupportedFormatError:
             logger.error("-" * 80)
             logger.error(" Input file does not appear to be a PE file.")
diff --git a/scripts/bulk-process.py b/scripts/bulk-process.py
index 584e8d66..14f1d8ac 100644
--- a/scripts/bulk-process.py
+++ b/scripts/bulk-process.py
@@ -96,7 +96,7 @@ def get_capa_results(args):
     rules, format, path = args
     logger.info("computing capa results for: %s", path)
     try:
-        extractor = capa.main.get_extractor(path, format, capa.main.BACKEND_VIV, disable_progress=True)
+        extractor = capa.main.get_extractor(path, format, capa.main.BACKEND_VIV, args.signatures, disable_progress=True)
     except capa.main.UnsupportedFormatError:
         # i'm 100% sure if multiprocessing will reliably raise exceptions across process boundaries.
         # so instead, return an object with explicit success/failure status.
@@ -140,7 +140,7 @@ def main(argv=None):
         argv = sys.argv[1:]
 
         parser = argparse.ArgumentParser(description="detect capabilities in programs.")
-        capa.main.install_common_args(parser, wanted={"rules"})
+        capa.main.install_common_args(parser, wanted={"rules", "signatures"})
         parser.add_argument("input", type=str, help="Path to directory of files to recursively analyze")
         parser.add_argument(
             "-n", "--parallelism", type=int, default=multiprocessing.cpu_count(), help="parallelism factor"
diff --git a/scripts/capa_as_library.py b/scripts/capa_as_library.py
index 87a2378a..2d1b8ddf 100644
--- a/scripts/capa_as_library.py
+++ b/scripts/capa_as_library.py
@@ -192,7 +192,7 @@ def render_dictionary(doc):
 def capa_details(file_path, output_format="dictionary"):
 
     # extract features and find capabilities
-    extractor = capa.main.get_extractor(file_path, "auto", capa.main.BACKEND_VIV, disable_progress=True)
+    extractor = capa.main.get_extractor(file_path, "auto", capa.main.BACKEND_VIV, sigpaths=[], disable_progress=True)
     capabilities, counts = capa.main.find_capabilities(rules, extractor, disable_progress=True)
 
     # collect metadata (used only to make rendering more complete)
diff --git a/scripts/lint.py b/scripts/lint.py
index 9e9e2e3c..893b8cfd 100644
--- a/scripts/lint.py
+++ b/scripts/lint.py
@@ -181,6 +181,9 @@ class ExampleFileDNE(Lint):
         return not found
 
 
+DEFAULT_SIGNATURES = capa.main.get_default_signatures()
+
+
 class DoesntMatchExample(Lint):
     name = "doesn't match on referenced example"
     recommendation = "Fix the rule logic or provide a different example"
@@ -203,7 +206,9 @@ class DoesntMatchExample(Lint):
                 continue
 
             try:
-                extractor = capa.main.get_extractor(path, "auto", capa.main.BACKEND_VIV, disable_progress=True)
+                extractor = capa.main.get_extractor(
+                    path, "auto", capa.main.BACKEND_VIV, sigpaths=DEFAULT_SIGNATURES, disable_progress=True
+                )
                 capabilities, meta = capa.main.find_capabilities(ctx["rules"], extractor, disable_progress=True)
             except Exception as e:
                 logger.error("failed to extract capabilities: %s %s %s", rule.name, path, e)
diff --git a/scripts/match-function-id.py b/scripts/match-function-id.py
new file mode 100644
index 00000000..c37702ba
--- /dev/null
+++ b/scripts/match-function-id.py
@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+"""
+Copyright (C) 2021 FireEye, Inc. All Rights Reserved.
+Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+You may obtain a copy of the License at: [package root]/LICENSE.txt
+Unless required by applicable law or agreed to in writing, software distributed under the License
+ is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and limitations under the License.
+
+match-function-id
+
+Show the names of functions as recognized by the function identification subsystem.
+This can help identify library functions statically linked into a program,
+such as when triaging false positive matches in capa rules.
+
+Example::
+
+    $ python scripts/match-function-id.py --signature sigs/vc6.pat.gz /tmp/suspicious.dll_
+    0x44cf30: ?GetPdbDll@@YAPAUHINSTANCE__@@XZ
+    0x44bb20: ?_strlen_priv@@YAIPBD@Z
+    0x44b6b0: ?invoke_main@@YAHXZ
+    0x44a5d0: ?find_pe_section@@YAPAU_IMAGE_SECTION_HEADER@@QAEI@Z
+    0x44a690: ?is_potentially_valid_image_base@@YA_NQAX@Z
+    0x44cbe0: ___get_entropy
+    0x44a4a0: __except_handler4
+    0x44b3d0: ?pre_cpp_initialization@@YAXXZ
+    0x44b2e0: ?pre_c_initialization@@YAHXZ
+    0x44b3c0: ?post_pgo_initialization@@YAHXZ
+    0x420156: ?
+    0x420270: ?
+    0x430dcd: ?
+    0x44d930: __except_handler4_noexcept
+    0x41e960: ?
+    0x44a1e0: @_RTC_AllocaHelper@12
+    0x44ba90: ?_getMemBlockDataString@@YAXPAD0PBDI@Z
+    0x44a220: @_RTC_CheckStackVars2@12
+    0x44a790: ___scrt_dllmain_after_initialize_c
+    0x44a7d0: ___scrt_dllmain_before_initialize_c
+    0x44a800: ___scrt_dllmain_crt_thread_attach
+    0x44a860: ___scrt_dllmain_exception_filter
+    0x44a900: ___scrt_dllmain_uninitialize_critical
+    0x44ad10: _at_quick_exit
+    0x44b940: ?_RTC_Failure@@YAXPAXH@Z
+    0x44be60: __RTC_UninitUse
+    0x44bfd0: __RTC_GetErrDesc
+    0x44c060: __RTC_SetErrorType
+    0x44cb60: ?
+    0x44cba0: __guard_icall_checks_enforced
+"""
+import sys
+import logging
+import argparse
+
+import flirt
+import viv_utils
+import viv_utils.flirt
+
+import capa.main
+import capa.rules
+import capa.engine
+import capa.helpers
+import capa.features
+import capa.features.freeze
+
+logger = logging.getLogger("capa.match-function-id")
+
+
+def main(argv=None):
+    if argv is None:
+        argv = sys.argv[1:]
+
+    parser = argparse.ArgumentParser(description="FLIRT match each function")
+    parser.add_argument("sample", type=str, help="Path to sample to analyze")
+    parser.add_argument(
+        "-F",
+        "--function",
+        type=lambda x: int(x, 0x10),
+        help="match a specific function by VA, rather than add functions",
+    )
+    parser.add_argument(
+        "--signature",
+        action="append",
+        dest="signatures",
+        type=str,
+        default=[],
+        help="use the given signatures to identify library functions, file system paths to .sig/.pat files.",
+    )
+    parser.add_argument("-d", "--debug", action="store_true", help="Enable debugging output on STDERR")
+    parser.add_argument("-q", "--quiet", action="store_true", help="Disable all output but errors")
+    args = parser.parse_args(args=argv)
+
+    if args.quiet:
+        logging.basicConfig(level=logging.ERROR)
+        logging.getLogger().setLevel(logging.ERROR)
+    elif args.debug:
+        logging.basicConfig(level=logging.DEBUG)
+        logging.getLogger().setLevel(logging.DEBUG)
+    else:
+        logging.basicConfig(level=logging.INFO)
+        logging.getLogger().setLevel(logging.INFO)
+
+    # disable vivisect-related logging, it's verbose and not relevant for capa users
+    capa.main.set_vivisect_log_level(logging.CRITICAL)
+
+    analyzers = []
+    for sigpath in args.signatures:
+        sigs = capa.main.load_flirt_signature(sigpath)
+
+        with capa.main.timing("flirt: compiling sigs"):
+            matcher = flirt.compile(sigs)
+
+        analyzer = viv_utils.flirt.FlirtFunctionAnalyzer(matcher, sigpath)
+        logger.debug("registering viv function analyzer: %s", repr(analyzer))
+        analyzers.append(analyzer)
+
+    vw = viv_utils.getWorkspace(args.sample, analyze=True, should_save=False)
+
+    functions = vw.getFunctions()
+    if args.function:
+        functions = [args.function]
+
+    for function in functions:
+        logger.debug("matching function: 0x%04x", function)
+        for analyzer in analyzers:
+            name = viv_utils.flirt.match_function_flirt_signatures(analyzer.matcher, vw, function)
+            if name:
+                print("0x%04x: %s" % (function, name))
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/scripts/show-capabilities-by-function.py b/scripts/show-capabilities-by-function.py
index 569e7534..f3d73710 100644
--- a/scripts/show-capabilities-by-function.py
+++ b/scripts/show-capabilities-by-function.py
@@ -111,7 +111,7 @@ def main(argv=None):
         argv = sys.argv[1:]
 
     parser = argparse.ArgumentParser(description="detect capabilities in programs.")
-    capa.main.install_common_args(parser, wanted={"format", "sample", "rules", "tag"})
+    capa.main.install_common_args(parser, wanted={"format", "backend", "sample", "signatures", "rules", "tag"})
     args = parser.parse_args(args=argv)
     capa.main.handle_common_args(args)
 
@@ -152,8 +152,9 @@ def main(argv=None):
             extractor = capa.features.freeze.load(f.read())
     else:
         format = args.format
+
         try:
-            extractor = capa.main.get_extractor(args.sample, args.format)
+            extractor = capa.main.get_extractor(args.sample, args.format, args.backend, args.signatures)
         except capa.main.UnsupportedFormatError:
             logger.error("-" * 80)
             logger.error(" Input file does not appear to be a PE file.")
diff --git a/scripts/show-features.py b/scripts/show-features.py
index f357ab51..8960deca 100644
--- a/scripts/show-features.py
+++ b/scripts/show-features.py
@@ -83,7 +83,7 @@ def main(argv=None):
         argv = sys.argv[1:]
 
     parser = argparse.ArgumentParser(description="Show the features that capa extracts from the given sample")
-    capa.main.install_common_args(parser, wanted={"format", "sample"})
+    capa.main.install_common_args(parser, wanted={"format", "sample", "signatures"})
 
     parser.add_argument("-F", "--function", type=lambda x: int(x, 0x10), help="Show features for specific function")
     args = parser.parse_args(args=argv)
@@ -100,7 +100,9 @@ def main(argv=None):
             extractor = capa.features.freeze.load(f.read())
     else:
         try:
-            extractor = capa.main.get_extractor(args.sample, args.format, capa.main.BACKEND_VIV)
+            extractor = capa.main.get_extractor(
+                args.sample, args.format, capa.main.BACKEND_VIV, sigpaths=args.signatures
+            )
         except capa.main.UnsupportedFormatError:
             logger.error("-" * 80)
             logger.error(" Input file does not appear to be a PE file.")
@@ -135,9 +137,9 @@ def main(argv=None):
         if args.format == "freeze":
             functions = tuple(filter(lambda f: f == args.function, functions))
         else:
-            functions = tuple(filter(lambda f: capa.helpers.oint(f) == args.function, functions))
+            functions = tuple(filter(lambda f: int(f) == args.function, functions))
 
-            if args.function not in [capa.helpers.oint(f) for f in functions]:
+            if args.function not in [int(f) for f in functions]:
                 print("0x%X not a function" % args.function)
                 return -1
 
diff --git a/setup.py b/setup.py
index 580a3be1..1b1c685a 100644
--- a/setup.py
+++ b/setup.py
@@ -7,7 +7,6 @@
 # See the License for the specific language governing permissions and limitations under the License.
 
 import os
-import sys
 
 import setuptools
 
@@ -19,7 +18,7 @@ requirements = [
     "termcolor==1.1.0",
     "wcwidth==0.2.5",
     "ida-settings==2.1.0",
-    "viv-utils==0.6.0",
+    "viv-utils[flirt]==0.6.2",
     "halo==0.0.31",
     "networkx==2.5.1",
     "ruamel.yaml==0.17.4",
diff --git a/sigs/README.md b/sigs/README.md
new file mode 100644
index 00000000..c2024fb3
--- /dev/null
+++ b/sigs/README.md
@@ -0,0 +1,9 @@
+# capa/sigs
+
+This directory contains FLIRT signatures that capa uses to identify library functions.
+Typically, capa will ignore library functions, which reduces false positives and improves runtime.
+
+These FLIRT signatures were generated by FireEye using the Hex-Rays FLAIR tools such as `pcf` and `sigmake`.
+FireEye generated the signatures from source data that they collected; these signatures are not derived from the FLIRT signatures distributed with IDA PRo.
+
+The signatures in this directory have the same license as capa: Apache 2.0.
\ No newline at end of file
diff --git a/sigs/flare_common_libs.sig b/sigs/flare_common_libs.sig
new file mode 100644
index 00000000..436b2046
Binary files /dev/null and b/sigs/flare_common_libs.sig differ
diff --git a/sigs/flare_msvc_atlmfc_32_64.sig b/sigs/flare_msvc_atlmfc_32_64.sig
new file mode 100644
index 00000000..a00aaafa
Binary files /dev/null and b/sigs/flare_msvc_atlmfc_32_64.sig differ
diff --git a/sigs/flare_msvc_rtf_32_64.sig b/sigs/flare_msvc_rtf_32_64.sig
new file mode 100644
index 00000000..0edf8f7d
Binary files /dev/null and b/sigs/flare_msvc_rtf_32_64.sig differ
diff --git a/sigs/test_aulldiv.pat b/sigs/test_aulldiv.pat
new file mode 100644
index 00000000..bbf3e52d
--- /dev/null
+++ b/sigs/test_aulldiv.pat
@@ -0,0 +1,11 @@
+# Copyright (C) 2020 FireEye, Inc. All Rights Reserved.
+# Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at: [package root]/LICENSE.txt
+# Unless required by applicable law or agreed to in writing, software distributed under the License
+#  is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and limitations under the License.
+53568b4424180bc075188b4c24148b44241033d2f7f18bd88b44240cf7f18bd3 48 d0a0 0068 :0000 __aulldiv
+558bec83e4e083ec60c5fe7f4c2420c5fe7f0424ff742424ff742424ff74240c 08 6e24 0095 :0000 ___avx_u64div4@@64 ^0028 __aulldiv
+558bec83e4f083ec30660f6fd1660f73da04660f6fd8660f7ed0660f73db04f3 1b ed6c 0080 :0000 ___sse2_u64div2@@32 ^003b __aulldiv
+---
\ No newline at end of file
diff --git a/sigs/test_aullrem.pat.gz b/sigs/test_aullrem.pat.gz
new file mode 100644
index 00000000..b63ee4f5
Binary files /dev/null and b/sigs/test_aullrem.pat.gz differ
diff --git a/tests/fixtures.py b/tests/fixtures.py
index b5a0b91d..33b0cc26 100644
--- a/tests/fixtures.py
+++ b/tests/fixtures.py
@@ -72,12 +72,15 @@ def xfail(condition, reason=None):
 def get_viv_extractor(path):
     import capa.features.extractors.viv
 
+    aulldiv_pat = os.path.join(CD, "..", "sigs", "test_aulldiv.pat")
+    aullrem_pat = os.path.join(CD, "..", "sigs", "test_aullrem.pat.gz")
+
     if "raw32" in path:
-        vw = capa.main.get_workspace(path, "sc32", should_save=False)
+        vw = capa.main.get_workspace(path, "sc32", sigpaths=[aulldiv_pat, aullrem_pat])
     elif "raw64" in path:
-        vw = capa.main.get_workspace(path, "sc64", should_save=False)
+        vw = capa.main.get_workspace(path, "sc64", sigpaths=[aulldiv_pat, aullrem_pat])
     else:
-        vw = capa.main.get_workspace(path, "auto", should_save=True)
+        vw = capa.main.get_workspace(path, "auto", sigpaths=[aulldiv_pat, aullrem_pat])
     extractor = capa.features.extractors.viv.VivisectFeatureExtractor(vw, path)
     fixup_viv(path, extractor)
     return extractor
@@ -241,14 +244,14 @@ def sample(request):
 
 def get_function(extractor, fva):
     for f in extractor.get_functions():
-        if f.__int__() == fva:
+        if int(f) == fva:
             return f
     raise ValueError("function not found")
 
 
 def get_basic_block(extractor, f, va):
     for bb in extractor.get_basic_blocks(f):
-        if bb.__int__() == va:
+        if int(bb) == va:
             return bb
     raise ValueError("basic block not found")
 
diff --git a/tests/test_freeze.py b/tests/test_freeze.py
index 4e27d5f8..514e98f3 100644
--- a/tests/test_freeze.py
+++ b/tests/test_freeze.py
@@ -115,30 +115,23 @@ def compare_extractors_viv_null(viv_ext, null_ext):
       null_ext (capa.features.extractors.NullFeatureExtractor)
     """
     assert list(viv_ext.extract_file_features()) == list(null_ext.extract_file_features())
-    assert list(map(to_int, viv_ext.get_functions())) == list(null_ext.get_functions())
+    assert list(map(int, viv_ext.get_functions())) == list(null_ext.get_functions())
     for f in viv_ext.get_functions():
-        assert list(map(to_int, viv_ext.get_basic_blocks(f))) == list(null_ext.get_basic_blocks(to_int(f)))
-        assert list(viv_ext.extract_function_features(f)) == list(null_ext.extract_function_features(to_int(f)))
+        assert list(map(int, viv_ext.get_basic_blocks(f))) == list(null_ext.get_basic_blocks(int(f)))
+        assert list(viv_ext.extract_function_features(f)) == list(null_ext.extract_function_features(int(f)))
 
         for bb in viv_ext.get_basic_blocks(f):
-            assert list(map(to_int, viv_ext.get_instructions(f, bb))) == list(
-                null_ext.get_instructions(to_int(f), to_int(bb))
-            )
+            assert list(map(int, viv_ext.get_instructions(f, bb))) == list(null_ext.get_instructions(int(f), int(bb)))
             assert list(viv_ext.extract_basic_block_features(f, bb)) == list(
-                null_ext.extract_basic_block_features(to_int(f), to_int(bb))
+                null_ext.extract_basic_block_features(int(f), int(bb))
             )
 
             for insn in viv_ext.get_instructions(f, bb):
                 assert list(viv_ext.extract_insn_features(f, bb, insn)) == list(
-                    null_ext.extract_insn_features(to_int(f), to_int(bb), to_int(insn))
+                    null_ext.extract_insn_features(int(f), int(bb), int(insn))
                 )
 
 
-def to_int(o):
-    """helper to get int value of extractor items"""
-    return capa.helpers.oint(o)
-
-
 def test_freeze_s_roundtrip():
     load = capa.features.freeze.loads
     dump = capa.features.freeze.dumps
diff --git a/tests/test_function_id.py b/tests/test_function_id.py
new file mode 100644
index 00000000..c6ad2be9
--- /dev/null
+++ b/tests/test_function_id.py
@@ -0,0 +1,27 @@
+from fixtures import get_function, pma16_01_extractor, extract_function_features
+
+import capa.features.insn
+
+
+def test_function_id_simple_match(pma16_01_extractor):
+    assert pma16_01_extractor.is_library_function(0x407490) == True
+    assert pma16_01_extractor.get_function_name(0x407490) == "__aulldiv"
+
+
+def test_function_id_gz_pat(pma16_01_extractor):
+    # aullrem is stored in `test_aullrem.pat.gz`
+    assert pma16_01_extractor.is_library_function(0x407500) == True
+    assert pma16_01_extractor.get_function_name(0x407500) == "__aullrem"
+
+
+def test_function_id_complex_match(pma16_01_extractor):
+    # 0x405714 is __spawnlp which requires recursive match of __spawnvp at 0x407FAB
+    # (and __spawnvpe at 0x409DE8)
+    assert pma16_01_extractor.is_library_function(0x405714) == True
+    assert pma16_01_extractor.get_function_name(0x405714) == "__spawnlp"
+
+
+def test_function_id_api_feature(pma16_01_extractor):
+    f = get_function(pma16_01_extractor, 0x404548)
+    features = extract_function_features(pma16_01_extractor, f)
+    assert capa.features.insn.API("__aulldiv") in features