From f12aa97aab4336e2203cebcdf1b1b3004be758f3 Mon Sep 17 00:00:00 2001
From: "Dmitry V. Levin" <ldv@altlinux.org>
Date: Sun, 29 Apr 2018 21:59:55 +0000
Subject: [PATCH] xlat: check that system definitions match fallback
 definitions

For each constant that is accompanied by a fallback definition,
generate a sanity check that the definition provided by system headers
matches the fallback definition.

* gcc_compat.h (DIAG_PUSH_IGNORE_TAUTOLOGICAL_COMPARE,
DIAG_POP_IGNORE_TAUTOLOGICAL_COMPARE): New macros.
* xlat/gen.sh (cond_def): Generate a code that checks the system
definition against the default.
(gen_header): Generate a code that includes "gcc_compat.h" and
"static_assert.h".

Co-Authored-by: Eugene Syromyatnikov <evgsyr@gmail.com>
---
 gcc_compat.h | 11 +++++++++++
 xlat/gen.sh  | 14 ++++++++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/gcc_compat.h b/gcc_compat.h
index 771286aa..251080bb 100644
--- a/gcc_compat.h
+++ b/gcc_compat.h
@@ -99,4 +99,15 @@
 # define ATTRIBUTE_FALLTHROUGH	((void) 0)
 #endif
 
+#if GNUC_PREREQ(6, 0)
+# define DIAG_PUSH_IGNORE_TAUTOLOGICAL_COMPARE				\
+	_Pragma("GCC diagnostic push");					\
+	_Pragma("GCC diagnostic ignored \"-Wtautological-compare\"");
+# define DIAG_POP_IGNORE_TAUTOLOGICAL_COMPARE				\
+	_Pragma("GCC diagnostic pop");
+#else
+# define DIAG_PUSH_IGNORE_TAUTOLOGICAL_COMPARE	/* empty */
+# define DIAG_POP_IGNORE_TAUTOLOGICAL_COMPARE	/* empty */
+#endif
+
 #endif /* !STRACE_GCC_COMPAT_H */
diff --git a/xlat/gen.sh b/xlat/gen.sh
index aff79922..82e246c5 100755
--- a/xlat/gen.sh
+++ b/xlat/gen.sh
@@ -53,7 +53,11 @@ cond_def()
 
 	if [ -n "$def" ]; then
 		cat <<-EOF
-		#if !(defined($val) || (defined(HAVE_DECL_$val) && HAVE_DECL_$val))
+		#if defined($val) || (defined(HAVE_DECL_$val) && HAVE_DECL_$val)
+		DIAG_PUSH_IGNORE_TAUTOLOGICAL_COMPARE
+		static_assert(($val) == ($def), "$val != $def");
+		DIAG_POP_IGNORE_TAUTOLOGICAL_COMPARE
+		#else
 		# define $val $def
 		#endif
 		EOF
@@ -133,7 +137,13 @@ gen_header()
 		in_mpers=1
 	fi
 
-	echo "/* Generated by $0 from $1; do not edit. */"
+	cat <<-EOF
+	/* Generated by $0 from $1; do not edit. */
+
+	#include "gcc_compat.h"
+	#include "static_assert.h"
+
+	EOF
 
 	local unconditional= line
 	# 1st pass: output directives.
-- 
2.40.0