bpo-26544: Fixed implementation of platform.libc_ver(). (GH-7684)

4 files changed, 23 insertions, 13 deletions

diff --git a/Doc/library/platform.rst b/Doc/library/platform.rst
index 5b2ff1b497b..92691fcbeab 100644
--- a/Doc/library/platform.rst
+++ b/Doc/library/platform.rst
@@ -243,7 +243,7 @@ Mac OS Platform
 Unix Platforms
 --------------
 
-.. function:: libc_ver(executable=sys.executable, lib='', version='', chunksize=2048)
+.. function:: libc_ver(executable=sys.executable, lib='', version='', chunksize=16384)
 
    Tries to determine the libc version against which the file executable (defaults
    to the Python interpreter) is linked.  Returns a tuple of strings ``(lib,
diff --git a/Lib/platform.py b/Lib/platform.py
index 6051f2b5901..a7785a22440 100755
--- a/Lib/platform.py
+++ b/Lib/platform.py
@@ -140,9 +140,7 @@ _libc_search = re.compile(b'(__libc_init)'
                           b'|'
                           br'(libc(_\w+)?\.so(?:\.(\d[0-9.]*))?)', re.ASCII)
 
-def libc_ver(executable=sys.executable, lib='', version='',
-
-             chunksize=16384):
+def libc_ver(executable=sys.executable, lib='', version='', chunksize=16384):
 
     """ Tries to determine the libc version that the file executable
         (which defaults to the Python interpreter) is linked against.
@@ -157,6 +155,7 @@ def libc_ver(executable=sys.executable, lib='', version='',
         The file is read and scanned in chunks of chunksize bytes.
 
     """
+    from distutils.version import LooseVersion as V
     if hasattr(os.path, 'realpath'):
         # Python 2.2 introduced os.path.realpath(); it is used
         # here to work around problems with Cygwin not being
@@ -165,17 +164,19 @@ def libc_ver(executable=sys.executable, lib='', version='',
     with open(executable, 'rb') as f:
         binary = f.read(chunksize)
         pos = 0
-        while 1:
+        while pos < len(binary):
             if b'libc' in binary or b'GLIBC' in binary:
                 m = _libc_search.search(binary, pos)
             else:
                 m = None
-            if not m:
-                binary = f.read(chunksize)
-                if not binary:
+            if not m or m.end() == len(binary):
+                chunk = f.read(chunksize)
+                if chunk:
+                    binary = binary[max(pos, len(binary) - 1000):] + chunk
+                    pos = 0
+                    continue
+                if not m:
                     break
-                pos = 0
-                continue
             libcinit, glibc, glibcversion, so, threads, soversion = [
                 s.decode('latin1') if s is not None else s
                 for s in m.groups()]
@@ -185,12 +186,12 @@ def libc_ver(executable=sys.executable, lib='', version='',
                 if lib != 'glibc':
                     lib = 'glibc'
                     version = glibcversion
-                elif glibcversion > version:
+                elif V(glibcversion) > V(version):
                     version = glibcversion
             elif so:
                 if lib != 'glibc':
                     lib = 'libc'
-                    if soversion and soversion > version:
+                    if soversion and (not version or V(soversion) > V(version)):
                         version = soversion
                     if threads and version[-len(threads):] != threads:
                         version = version + threads
@@ -253,6 +254,7 @@ def popen(cmd, mode='r', bufsize=-1):
     warnings.warn('use os.popen instead', DeprecationWarning, stacklevel=2)
     return os.popen(cmd, mode, bufsize)
 
+
 def _norm_version(version, build=''):
 
     """ Normalize the version and build strings and return a single
diff --git a/Lib/test/test_platform.py b/Lib/test/test_platform.py
index 7e3e40114b4..9ecd5d904e3 100644
--- a/Lib/test/test_platform.py
+++ b/Lib/test/test_platform.py
@@ -260,7 +260,6 @@ class PlatformTest(unittest.TestCase):
             self.assertEqual(sts, 0)
 
     def test_libc_ver(self):
-        import os
         if os.path.isdir(sys.executable) and \
            os.path.exists(sys.executable+'.exe'):
             # Cygwin horror
@@ -269,6 +268,13 @@ class PlatformTest(unittest.TestCase):
             executable = sys.executable
         res = platform.libc_ver(executable)
 
+        self.addCleanup(support.unlink, support.TESTFN)
+        with open(support.TESTFN, 'wb') as f:
+            f.write(b'x'*(16384-10))
+            f.write(b'GLIBC_1.23.4\0GLIBC_1.9\0GLIBC_1.21\0')
+        self.assertEqual(platform.libc_ver(support.TESTFN),
+                         ('glibc', '1.23.4'))
+
     def test_popen(self):
         mswindows = (sys.platform == "win32")
 
diff --git a/Misc/NEWS.d/next/Library/2018-06-13-20-33-29.bpo-26544.hQ1oMt.rst b/Misc/NEWS.d/next/Library/2018-06-13-20-33-29.bpo-26544.hQ1oMt.rst
new file mode 100644
index 00000000000..e2cd0bad6e2
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-06-13-20-33-29.bpo-26544.hQ1oMt.rst
@@ -0,0 +1,2 @@
+Fixed implementation of :func:`platform.libc_ver`. It almost always returned
+version '2.9' for glibc.