[tsan] Fix "failed to intercept sysctlnametomib" on FreeBSD

[arichardson]

Summary

The sysctlnametomib function is called from tsan::Initialize via
sanitizer::internal_sysctlbyname (see stack trace below). This results
in a fatal error since sysctlnametomib has not been intercepted yet.
This patch allows internal_sysctlbyname to be called before
__tsan::Initialize() has completed. On FreeBSD >= 1300045 sysctlbyname()
is a real syscall, but for older versions it calls sysctlnametomib()
followed by sysctl(). To avoid calling the intercepted version, look up
the real sysctlnametomib() followed by internal_sysctl() if the
syscall is not available.

This reduces check-sanitizer failures from 62 to 11 for me.

34433==FATAL: ThreadSanitizer: failed to intercept sysctlnametomib

#0 __sanitizer::Die ()

at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_termination.cpp:51

#1 0x00000000002a2de6 in __interceptor_sysctlnametomib (sname=0x2146cb "kern.elf64.aslr.pie_enable",

name=0x7fffffffce10, namelenp=0x7fffffffce08)
at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/tsan/../sanitizer_common/sanitizer_common_interceptors.inc:7908

#2 0x000000080061ea0d in sysctlbyname () from /lib/libc.so.7
#3 0x00000000002515a0 in __sanitizer::internal_sysctlbyname (sname=0x2146cb "kern.elf64.aslr.pie_enable",

oldp=0x7fffffffcf2c, oldlenp=0x7fffffffcf20, newp=0x0, newlen=0)
at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp:803

#4 0x0000000000252823 in __sanitizer::CheckASLR ()

at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp:2152

#5 0x00000000002dd2ea in __tsan::Initialize (thr=0x800901980)

at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp:367

#6 0x000000000027cdd0 in __tsan::ScopedInterceptor::ScopedInterceptor (this=0x7fffffffd030, thr=0x800901980,

fname=0x21c731 "readlink", pc=34366042556)
at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp:255

#7 0x00000000002a0055 in __interceptor_readlink (path=0x80051d509 "/etc/malloc.conf", buf=0x7fffffffd0b0 "",

bufsiz=1024)
at /exports/users/alr48/sources/upstream-llvm-project/compiler-rt/lib/tsan/../sanitizer_common/sanitizer_common_interceptors.inc:7151

#8 0x00000008006031bc in ?? () from /lib/libc.so.7
#9 0x0000000800602b08 in ?? () from /lib/libc.so.7
#10 0x000000080032646e in ?? () from /libexec/ld-elf.so.1
#11 0x0000000000000000 in ?? ()

[arichardson]

ping.

[vitalybuka]

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

813–826

Why not like this?

[vitalybuka]

Accepted by mistake

[arichardson]

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

813–826

Yeah that's probably better. I initially wanted to fall through to doing the old way on ENOSYS, but it turns out that we get a SIGSYS instead. Just returning the error code seems better unless we really want to support building the sanitizer runtime on a new OS and running it on an old kernel.

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

#else
   return internal_syscall(SYSCALL(__sysctl), name, namelen, oldp,
                           (size_t *)oldlenp, newp, (size_t)newlen);
 #endif
 }
 
 #if SANITIZER_FREEBSD
 int internal_sysctlbyname(const char *sname, void *oldp, uptr *oldlenp,
                           const void *newp, uptr newlen) {
-  static decltype(sysctlbyname) *real = nullptr;
-  if (!real)
-    real = (decltype(sysctlbyname) *)dlsym(RTLD_NEXT, "sysctlbyname");
-  CHECK(real);
-  return real(sname, oldp, (size_t *)oldlenp, newp, (size_t)newlen);
+  // Note: this function can be called during startup, so we need to avoid
+  // calling any interceptable functions. On FreeBSD >= 1300045 sysctlbyname()
+  // is a real syscall, but for older versions it calls sysctlnametomib()
+  // followed by sysctl(). To avoid calling the intercepted version and
+  // asserting if this happens during startup, call the real sysctlnametomib()
+  // followed by internal_sysctl() if the syscall is not available.
+#ifdef SYS___sysctlbyname
+  return internal_syscall(SYSCALL(__sysctlbyname), sname,
+                          internal_strlen(sname), oldp, (size_t *)oldlenp, newp,
+                          (size_t)newlen);
+#else
+  static decltype(sysctlnametomib) *real_sysctlnametomib = nullptr;
+  if (!real_sysctlnametomib)
+    real_sysctlnametomib =
+        (decltype(sysctlnametomib) *)dlsym(RTLD_NEXT, "sysctlnametomib");
+  CHECK(real_sysctlnametomib);
+
+  int oid[CTL_MAXNAME];
+  size_t len = CTL_MAXNAME;
+  if (real_sysctlnametomib(sname, oid, &len) == -1)
+    return (-1);
+  return internal_sysctl(oid, len, oldp, oldlenp, newp, newlen);
+#endif
 }
 #endif
 #endif
 
 #if SANITIZER_LINUX
 #define SA_RESTORER 0x04000000
 // Doesn't set sa_restorer if the caller did not set it, so use with caution
 //(see below).
 int internal_sigaction_norestorer(int signum, const void *act, void *oldact) {