linux-hardening - [PATCH] gcc-plugins: avoid errors with -std=gnu++11 on old gcc

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Message-ID: <104383.1610566503@turing-police>
Date:   Wed, 13 Jan 2021 14:35:03 -0500
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] gcc-plugins: avoid errors with -std=gnu++11 on old gcc

It turns out that older gcc (4.9 and 5.4) have gnu++11 support, but
due to a gcc bug fixed in gcc6, throw errors during the build.
The relevant gcc bug is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69959

Version the option based on what gcc we're using.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@...edu>
Fixes: 27c287b41659 ("gcc-plugins: fix gcc 11 indigestion with plugins...")
---
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index b5487cce69e8..cc779973724a 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -21,8 +21,11 @@ always-y += $(GCC_PLUGIN)
 
 GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
 
+# need gnu++11 for gcc 11, but 4.9 and 5.4 need gnu++98
+GCC_FLAVOR = $(call cc-ifversion, -ge, 1100, 11, 98)
+
 plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
-		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++11 \
+		   -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++$(GCC_FLAVOR) \
 		   -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
 		   -ggdb -Wno-narrowing -Wno-unused-variable \
 		   -Wno-format-diag