release: Add security/export checks to gitian and fix current failures

- fix parsing of BIND_NOW with older readelf
- add _IO_stdin_used to ignored exports

For details see: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=634261#109

- add check-symbols and check-security make targets

These are not added to the default checks because some of them depend on
release-build configs.

- always link librt for glibc back-compat builds

glibc absorbed clock_gettime in 2.17. librt (its previous location) is safe to
link in anyway for back-compat.

Fixes #7420

- add security/symbol checks to gitian

Github-Pull: #7424
Rebased-From: cd27bf51e0 475813ba5b f3d3eaf78e a8ce872118 a81c87fafc

contrib/devtools/security-check.py

@@ -94,7 +94,7 @@ def check_ELF_RELRO(executable):
         raise IOError('Error opening file')
     for line in stdout.split('\n'):
         tokens = line.split()
-        if len(tokens)>1 and tokens[1] == '(BIND_NOW)':
+        if len(tokens)>1 and tokens[1] == '(BIND_NOW)' or (len(tokens)>2 and tokens[1] == '(FLAGS)' and 'BIND_NOW' in tokens[2]):
             have_bindnow = True
     return have_gnu_relro and have_bindnow
 

contrib/devtools/symbol-check.py

@@ -42,9 +42,12 @@ MAX_VERSIONS = {
 'GLIBCXX': (3,4,13),
 'GLIBC':   (2,11)
 }
+# See here for a description of _IO_stdin_used:
+# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=634261#109
+
 # Ignore symbols that are exported as part of every executable
 IGNORE_EXPORTS = {
-'_edata', '_end', '_init', '__bss_start', '_fini'
+'_edata', '_end', '_init', '__bss_start', '_fini', '_IO_stdin_used'
 }
 READELF_CMD = os.getenv('READELF', '/usr/bin/readelf')
 CPPFILT_CMD = os.getenv('CPPFILT', '/usr/bin/c++filt')