[DFSan] Add custom wrapper for _dl_get_tls_static_info.

[morehouse]

Summary

Implementation is here:
https://code.woboq.org/userspace/glibc/elf/dl-tls.c.html#307

We use weak symbols to avoid linking issues with glibcs older than 2.27.

compiler-rt/lib/dfsan/dfsan_custom.cpp

int (*callback_trampoline)(void *callback, struct dl_phdr_info *info,
                                dfsan_label *ret_label),
     void *callback, void *data, dfsan_label callback_label,
     dfsan_label data_label, dfsan_label *ret_label) {
   dl_iterate_phdr_info dipi = { callback_trampoline, callback, data };
   *ret_label = 0;
   return dl_iterate_phdr(dl_iterate_phdr_cb, &dipi);
 }
 
+// This function is only available for glibc 2.27 or newer.  Mark it weak so
+// linking succeeds with older glibcs.
+SANITIZER_WEAK_ATTRIBUTE void _dl_get_tls_static_info(size_t *sizep,
+                                                      size_t *alignp);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __dfsw__dl_get_tls_static_info(
+    size_t *sizep, size_t *alignp, dfsan_label sizep_label,
+    dfsan_label alignp_label) {
+  assert(_dl_get_tls_static_info);
+  _dl_get_tls_static_info(sizep, alignp);
+  dfsan_set_label(0, sizep, sizeof(*sizep));
+  dfsan_set_label(0, alignp, sizeof(*alignp));
+}
+
 SANITIZER_INTERFACE_ATTRIBUTE
 char *__dfsw_ctime_r(const time_t *timep, char *buf, dfsan_label timep_label,
                      dfsan_label buf_label, dfsan_label *ret_label) {
   char *ret = ctime_r(timep, buf);
   if (ret) {
     dfsan_set_label(dfsan_read_label(timep, sizeof(time_t)), buf,
                     strlen(buf) + 1);
     *ret_label = buf_label;

compiler-rt/lib/dfsan/done_abilist.txt

 fun:strcspn=discard
 fun:symlink=discard
 fun:syscall=discard
 fun:unlink=discard
 fun:uselocale=discard
 
 # Functions that produce output does not depend on the input (need to zero the
 # shadow manually).
+fun:_dl_get_tls_static_info=custom
 fun:calloc=custom
 fun:clock_gettime=custom
 fun:dlopen=custom
 fun:epoll_wait=custom
 fun:fgets=custom
 fun:fstat=custom
 fun:getcwd=custom
 fun:get_current_dir_name=custom

compiler-rt/test/dfsan/custom.cpp

int dl_iterate_phdr_test_cb(struct dl_phdr_info *info, size_t size,
   ASSERT_ZERO_LABEL(data);
   return 0;
 }
 
 void test_dl_iterate_phdr() {
   dl_iterate_phdr(dl_iterate_phdr_test_cb, (void *)3);
 }
 
+// On glibc < 2.27, this symbol is not available.  Mark it weak so we can skip
+// testing in this case.
+__attribute__((weak)) extern "C" void _dl_get_tls_static_info(size_t *sizep,
+                                                              size_t *alignp);
+
+void test__dl_get_tls_static_info() {
+  if (!_dl_get_tls_static_info)
+    return;
+  size_t sizep = 0, alignp = 0;
+  dfsan_set_label(i_label, &sizep, sizeof(sizep));
+  dfsan_set_label(i_label, &alignp, sizeof(alignp));
+  _dl_get_tls_static_info(&sizep, &alignp);
+  ASSERT_ZERO_LABEL(sizep);
+  ASSERT_ZERO_LABEL(alignp);
+}
+
 void test_strrchr() {
   char str1[] = "str1str1";
   dfsan_set_label(i_label, &str1[7], 1);
 
   char *rv = strrchr(str1, 'r');
   assert(rv == &str1[6]);
 #ifdef STRICT_DATA_DEPENDENCIES
   ASSERT_ZERO_LABEL(rv);
#else
   j_label = dfsan_create_label("j", 0);
   k_label = dfsan_create_label("k", 0);
 #endif
   i_j_label = dfsan_union(i_label, j_label);
   assert(i_j_label != i_label);
   assert(i_j_label != j_label);
   assert(i_j_label != k_label);
 
+  test__dl_get_tls_static_info();
   test_bcmp();
   test_calloc();
   test_clock_gettime();
   test_ctime_r();
   test_dfsan_set_write_callback();
   test_dl_iterate_phdr();
   test_dlopen();
   test_epoll_wait();