[PATCH] Fix libsanitizer on i?86-linux with glibc 2.27+ (PR sanitizer/84761)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

As mentioned in the PR, libsanitizer cheats and attempts to call
@GLIBC_PRIVATE functions which are reserved to glibc and can change
anytime.  They have changed on i?86 in particular in glibc 2.27, where
internal_function attribute has been dropped, so the functions for some
reason sadly aren't regparm(3) anymore.

This patch changes libsanitizer, so that when built against glibc 2.26 and
earlier, it checks at runtime if glibc 2.27+ is used using a symbol that has
been added ~ a month after the internal_function change, and when built
against glibc 2.27+, it just assumes it will never be regparm(3).

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

I've submitted it to upstream in https://reviews.llvm.org/D44623 too, but
it might take some time to get it through there.

2018-03-19  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/84761
	* sanitizer_common/sanitizer_linux_libcdep.cc (__GLIBC_PREREQ):
	Define if not defined.
	(DL_INTERNAL_FUNCTION): Don't define.
	(InitTlsSize): For __i386__ if not compiled against glibc 2.27+
	determine at runtime whether to use regparm(3), stdcall calling
	convention for older glibcs or normal calling convention for
	newer glibcs for call to _dl_get_tls_static_info.

--- libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cc.jj	2017-10-19 13:20:58.972958379 +0200
+++ libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cc	2018-03-19 14:05:56.178952563 +0100
@@ -147,29 +147,44 @@ bool SanitizerGetThreadName(char *name,
 #endif
 }
 
+#ifndef __GLIBC_PREREQ
+#define __GLIBC_PREREQ(x, y) 0
+#endif
+
 #if !SANITIZER_FREEBSD && !SANITIZER_ANDROID && !SANITIZER_GO && \
     !SANITIZER_NETBSD
 static uptr g_tls_size;
 
-#ifdef __i386__
-# define DL_INTERNAL_FUNCTION __attribute__((regparm(3), stdcall))
-#else
-# define DL_INTERNAL_FUNCTION
-#endif
-
 void InitTlsSize() {
 // all current supported platforms have 16 bytes stack alignment
   const size_t kStackAlign = 16;
-  typedef void (*get_tls_func)(size_t*, size_t*) DL_INTERNAL_FUNCTION;
-  get_tls_func get_tls;
-  void *get_tls_static_info_ptr = dlsym(RTLD_NEXT, "_dl_get_tls_static_info");
-  CHECK_EQ(sizeof(get_tls), sizeof(get_tls_static_info_ptr));
-  internal_memcpy(&get_tls, &get_tls_static_info_ptr,
-                  sizeof(get_tls_static_info_ptr));
-  CHECK_NE(get_tls, 0);
   size_t tls_size = 0;
   size_t tls_align = 0;
-  get_tls(&tls_size, &tls_align);
+  void *get_tls_static_info_ptr = dlsym(RTLD_NEXT, "_dl_get_tls_static_info");
+#if defined(__i386__) && !__GLIBC_PREREQ(2, 27)
+  /* On i?86, _dl_get_tls_static_info used to be internal_function, i.e.
+     __attribute__((regparm(3), stdcall)) before glibc 2.27 and is normal
+     function in 2.27 and later.  */
+  if (!dlvsym(RTLD_NEXT, "glob", "GLIBC_2.27")) {
+    typedef void (*get_tls_func)(size_t*, size_t*)
+      __attribute__((regparm(3), stdcall));
+    get_tls_func get_tls;
+    CHECK_EQ(sizeof(get_tls), sizeof(get_tls_static_info_ptr));
+    internal_memcpy(&get_tls, &get_tls_static_info_ptr,
+                    sizeof(get_tls_static_info_ptr));
+    CHECK_NE(get_tls, 0);
+    get_tls(&tls_size, &tls_align);
+  } else
+#endif
+  {
+    typedef void (*get_tls_func)(size_t*, size_t*);
+    get_tls_func get_tls;
+    CHECK_EQ(sizeof(get_tls), sizeof(get_tls_static_info_ptr));
+    internal_memcpy(&get_tls, &get_tls_static_info_ptr,
+                    sizeof(get_tls_static_info_ptr));
+    CHECK_NE(get_tls, 0);
+    get_tls(&tls_size, &tls_align);
+  }
   if (tls_align < kStackAlign)
     tls_align = kStackAlign;
   g_tls_size = RoundUpTo(tls_size, tls_align);

	Jakub