[sanitizer] Add early call handling to strchr + strrchr interceptors

[bruening]

Summary

The strchr and strrchr interceptors are sometimes invoked too early for
their REAL() counterparts to be initialized. A special check is added to
use internal_ routines for this situation.

[aizatsky]

Do these calls happen in libc? What's the reproducer? I wonder if there are any correctness implications because of this.

[bruening]

In D19607#414342, @aizatsky wrote:

Do these calls happen in libc? What's the reproducer? I wonder if there are any correctness implications because of this.

These are seen only with certain hooks invoked from tcmalloc on the dlsym() used in initializing interceptors. The other sanitizers all either use a custom allocator or avoid tcmalloc, while we'd prefer to leave the app heap layout as-is to better study its memory behavior, explaining why this was not seen before.

[filcab]

Please add the information you gave in your answer to Mike to the commit message. Just a small example will do.
Something like:
"We have seen this in hooks invoked from tcmalloc on the dlsym() used in initializing interceptors" would be enough.

Thank you!

[bruening]

In D19607#414508, @filcab wrote:

Please add the information you gave in your answer to Mike to the commit message. Just a small example will do.
Something like:
"We have seen this in hooks invoked from tcmalloc on the dlsym() used in initializing interceptors" would be enough.

Will do.

lib/sanitizer_common/sanitizer_common_interceptors.inc

 #define INIT_STRCASESTR COMMON_INTERCEPT_FUNCTION(strcasestr);
 #else
 #define INIT_STRCASESTR
 #endif
 
 #if SANITIZER_INTERCEPT_STRCHR
 INTERCEPTOR(char*, strchr, const char *s, int c) {
   void *ctx;
+  if (COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED)
+    return internal_strchr(s, c);
   COMMON_INTERCEPTOR_ENTER(ctx, strchr, s, c);
   char *result = REAL(strchr)(s, c);
   uptr len = internal_strlen(s);
   uptr n = result ? result - s + 1 : len + 1;
   if (common_flags()->intercept_strchr)
     COMMON_INTERCEPTOR_READ_STRING_OF_LEN(ctx, s, len, n);
   return result;
 }

 #define INIT_STRCHRNUL COMMON_INTERCEPT_FUNCTION(strchrnul)
 #else
 #define INIT_STRCHRNUL
 #endif
 
 #if SANITIZER_INTERCEPT_STRRCHR
 INTERCEPTOR(char*, strrchr, const char *s, int c) {
   void *ctx;
+  if (COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED)
+    return internal_strrchr(s, c);
   COMMON_INTERCEPTOR_ENTER(ctx, strrchr, s, c);
   uptr len = internal_strlen(s);
   if (common_flags()->intercept_strchr)
     COMMON_INTERCEPTOR_READ_STRING_OF_LEN(ctx, s, len, len + 1);
   return REAL(strrchr)(s, c);
 }
 #define INIT_STRRCHR COMMON_INTERCEPT_FUNCTION(strrchr)
 #else