From 20a30922fbf6ba14e250ca649239af115dbbe7b0 Mon Sep 17 00:00:00 2001
From: fanquake <fanquake@gmail.com>
Date: Sun, 19 Apr 2020 20:20:06 +0800
Subject: [PATCH] doc: note why we can't use thread_local with glibc back
 compat

---
 configure.ac | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/configure.ac b/configure.ac
index 4c9902efc6..77cd23c0b0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -861,6 +861,9 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
   ]
 )
 
+dnl thread_local is currently disabled when building with glibc back compat.
+dnl Our minimum supported glibc is 2.17, however support for thread_local
+dnl did not arrive in glibc until 2.18.
 if test "x$use_thread_local" = xyes || { test "x$use_thread_local" = xauto && test "x$use_glibc_compat" = xno; }; then
   TEMP_LDFLAGS="$LDFLAGS"
   LDFLAGS="$TEMP_LDFLAGS $PTHREAD_CFLAGS"