[compiler-rt] Fall back to internal_uname() when called early

[iii]

Summary

Commit 5f5fb56c68e4 ("[compiler-rt] Intercept the uname() function")
broke sanitizer-x86_64-linux and clang-cmake-thumbv7-full-sh (again)
builds:

http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/26313
http://lab.llvm.org:8011/builders/clang-cmake-thumbv7-full-sh/builds/4324

The reason is that uname() can be called as early as
__pthread_initialize_minimal_internal(). When intercepted, this
triggers ASan initialization, which eventually calls dlerror(), which
in turn uses pthreads, causing all sorts of issues.

Fix by falling back to internal_uname() when interceptor runs before
ASan is initialized. This is only for Linux at the moment.

[eugenis]

It looks like msan does not define COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED.
Does it need to? Why is it not broken the same way right now?

[iii]

msan does not call Symbolizer::LateInitialize(), which is Symbolizer::GetOrInit() + InitializeSwiftDemangler(). It calls only Symbolizer::GetOrInit(), and it's exactly InitializeSwiftDemangler() that triggers dlerror(). So for now it looks safe, but not particularly future-proof. #define COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED (!msan_inited) might be a good idea. Should I try to do this here, or separately?

[eugenis]

Sounds like a good idea, as a separate change.
Thank you!
LGTM

[vitalybuka]

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc

9751

Can you please remove "#if SANITIZER_LINUX" ?
I don't see why we need this constrain.

[iii]

internal_uname() is available only on Linux right now. I thought it's ok to postpone adding macOS/*BSD/etc implementations until that is really necessary.

[vitalybuka]

In D76919#1947069, @iii wrote:

internal_uname() is available only on Linux right now. I thought it's ok to postpone adding macOS/*BSD/etc implementations until that is really necessary.

ack

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc

 }
 #define INIT_SIGALTSTACK COMMON_INTERCEPT_FUNCTION(sigaltstack)
 #else
 #define INIT_SIGALTSTACK
 #endif
 
 #if SANITIZER_INTERCEPT_UNAME
 INTERCEPTOR(int, uname, struct utsname *utsname) {
+#if SANITIZER_LINUX
+  if (COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED)
+    return internal_uname(utsname);
+#endif
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, uname, utsname);
   int res = REAL(uname)(utsname);
   if (!res)
     COMMON_INTERCEPTOR_WRITE_RANGE(ctx, utsname,
                                    __sanitizer::struct_utsname_sz);
   return res;
 }