From b38042f51430974642616a60afbbf96fd0b98659 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Mon, 4 Sep 2017 10:52:28 +0200
Subject: [PATCH] math.h: Warn about an already-defined log macro

This is a common programming error, and the cause of the problem is not
always obvious.

<tgmath.h> defines a log macro, but it includes <math.h> before that, so
that is compatible with the warning.
---
 ChangeLog   | 4 ++++
 math/math.h | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index ef4a6edc5e..a9fb242bf2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2017-09-04  Florian Weimer  <fweimer@redhat.com>
+
+	* math/math.h: Issue warning if log is defined.
+
 2017-09-04  Joseph Myers  <joseph@codesourcery.com>
 
 	* scripts/build-many-glibcs.py (Context.checkout): Default Linux
diff --git a/math/math.h b/math/math.h
index 547b36d10e..6c2ad97fb8 100644
--- a/math/math.h
+++ b/math/math.h
@@ -26,6 +26,11 @@
 #define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
 #include <bits/libc-header-start.h>
 
+#if defined log && defined __GNUC__
+# warning A macro called log was already defined when <math.h> was included.
+# warning This will cause compilation problems.
+#endif
+
 __BEGIN_DECLS
 
 /* Get definitions of __intmax_t and __uintmax_t.  */
-- 
2.43.5