commit d2b8de2cd16ecd86c830d98c58bcf392475bd0b3
author Elliott Hughes <enh@google.com> Fri Mar 04 18:25:57 2016 -0800
committer Elliott Hughes <enh@google.com> Fri Mar 04 18:28:53 2016 -0800
tree ebd7f6cc626c63e3db8fbdb9dc3a6a8858922655
parent c4d2bede1592dd82dce9bfc6ebecdc414a79490b

Don't call clock_getres in sysconf.

There are a hundred other reasons why we can't run on kernels old enough
to not have all the clocks covered by sysconf.

This was causing trouble for jemalloc 4.1.0 in a seccomp-constrained process
because jemalloc 4.1.0 introduced a call to sysconf that caused us to make
clock_getres syscalls for the first time, leading to SIGSYS.

Bug: http://b/27408522
Change-Id: I2eb6986d871bc03cbef278e5617734409c39e057

libc/bionic/sysconf.cpp

diff --git a/libc/bionic/sysconf.cpp b/libc/bionic/sysconf.cpp
index 8a55f7e..125b3c9 100644
--- a/libc/bionic/sysconf.cpp
+++ b/libc/bionic/sysconf.cpp
@@ -41,16 +41,6 @@
 
 #include "private/bionic_tls.h"
 
-static int __sysconf_monotonic_clock() {
-  timespec t;
-  int rc = clock_getres(CLOCK_MONOTONIC, &t);
-  return (rc == -1) ? -1 : _POSIX_VERSION;
-}
-
-static bool __sysconf_has_clock(clockid_t clock_id) {
-  return clock_getres(clock_id, NULL) == 0;
-}
-
 static long __sysconf_rlimit(int resource) {
   rlimit rl;
   getrlimit(resource, &rl);
@@ -147,7 +137,7 @@
     case _SC_NPROCESSORS_ONLN:  return get_nprocs();
     case _SC_PHYS_PAGES:        return get_phys_pages();
     case _SC_AVPHYS_PAGES:      return get_avphys_pages();
-    case _SC_MONOTONIC_CLOCK:   return __sysconf_monotonic_clock();
+    case _SC_MONOTONIC_CLOCK:   return _POSIX_VERSION;
 
     case _SC_2_PBS:             return -1;     // Obsolescent in POSIX.1-2008.
     case _SC_2_PBS_ACCOUNTING:  return -1;     // Obsolescent in POSIX.1-2008.
@@ -158,8 +148,7 @@
     case _SC_ADVISORY_INFO:     return _POSIX_ADVISORY_INFO;
     case _SC_BARRIERS:          return _POSIX_BARRIERS;
     case _SC_CLOCK_SELECTION:   return _POSIX_CLOCK_SELECTION;
-    case _SC_CPUTIME:
-      return __sysconf_has_clock(CLOCK_PROCESS_CPUTIME_ID) ?_POSIX_VERSION : -1;
+    case _SC_CPUTIME:           return _POSIX_VERSION;
 
     case _SC_HOST_NAME_MAX:     return _POSIX_HOST_NAME_MAX;    // Minimum requirement.
     case _SC_IPV6:              return _POSIX_IPV6;
@@ -172,8 +161,7 @@
     case _SC_SPORADIC_SERVER:   return _POSIX_SPORADIC_SERVER;
     case _SC_SS_REPL_MAX:       return -1;
     case _SC_SYMLOOP_MAX:       return _POSIX_SYMLOOP_MAX;      // Minimum requirement.
-    case _SC_THREAD_CPUTIME:
-      return __sysconf_has_clock(CLOCK_THREAD_CPUTIME_ID) ? _POSIX_VERSION : -1;
+    case _SC_THREAD_CPUTIME:    return _POSIX_VERSION;
 
     case _SC_THREAD_PROCESS_SHARED: return _POSIX_THREAD_PROCESS_SHARED;
     case _SC_THREAD_ROBUST_PRIO_INHERIT:  return _POSIX_THREAD_ROBUST_PRIO_INHERIT;