diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 610abcd8c0a..0170e1e8416 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2018-06-12  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR target/85990
+	* config/i386/gnu-user.h (TARGET_THREAD_SPLIT_STACK_OFFSET):
+	Update comments.
+	* config/i386/gnu-user64.h (TARGET_THREAD_SPLIT_STACK_OFFSET):
+	Likewise.
+
 2018-06-12  Martin Liska  <mliska@suse.cz>
 
 	* doc/options.texi: Document IntegerRange.
diff --git a/gcc/config/i386/gnu-user.h b/gcc/config/i386/gnu-user.h
index d1dad685e72..56449a5439e 100644
--- a/gcc/config/i386/gnu-user.h
+++ b/gcc/config/i386/gnu-user.h
@@ -134,6 +134,6 @@ along with GCC; see the file COPYING3.  If not see
 /* i386 glibc provides __stack_chk_guard in %gs:0x14.  */
 #define TARGET_THREAD_SSP_OFFSET	0x14
 
-/* We steal the last transactional memory word.  */
+/* i386 glibc provides __private_ss in %gs:0x30.  */
 #define TARGET_THREAD_SPLIT_STACK_OFFSET 0x30
 #endif
diff --git a/gcc/config/i386/gnu-user64.h b/gcc/config/i386/gnu-user64.h
index 491416fec0c..f7a68fdecf0 100644
--- a/gcc/config/i386/gnu-user64.h
+++ b/gcc/config/i386/gnu-user64.h
@@ -86,7 +86,9 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define TARGET_THREAD_SSP_OFFSET \
   (TARGET_64BIT ? (TARGET_X32 ? 0x18 : 0x28) : 0x14)
 
-/* We steal the last transactional memory word.  */
+/* i386 glibc provides __private_ss in %gs:0x30.
+   x32 glibc provides it in %fs:0x40.
+   x86_64 glibc provides it in %fs:0x70.  */
 #define TARGET_THREAD_SPLIT_STACK_OFFSET \
   (TARGET_64BIT ? (TARGET_X32 ? 0x40 : 0x70) : 0x30)
 #endif