linux-kernel - Re: [PATCH] compiler-gcc: get back Clang build

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Date:   Tue, 21 Aug 2018 03:39:43 -0700
From:   Joe Perches <joe@...ches.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Arnd Bergmann <arnd@...db.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] compiler-gcc: get back Clang build

On Tue, 2018-08-21 at 15:48 +0900, Masahiro Yamada wrote:
> Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
> missed the fact that <linux/compiler-gcc.h> is included by Clang
> as well as by GCC.
> 
> Clang actually defines __GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__
> and it looks like GCC 4.2.1.
> 
>   $ scripts/gcc-version.sh -p clang
>   040201

Perhaps this would work, but I can't test it as
my clang version doesn't otherwise build a defconfig
and errors out with

$ make CC=clang
arch/x86/Makefile:179: *** Compiler lacks asm-goto support..  Stop.

---
 include/linux/compiler-gcc.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 3e70b7d4e9ed..3a06ad823fa4 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -3,6 +3,23 @@
 #error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
 #endif
 
+/*
+ * Override clang compiler version #defines
+ *
+ * compiler_types.h always #includes compiler-gcc.h before compiler-clang,h
+ * but clang sets these __GNUC version #defines to 4.2.1.
+ * This breaks the gcc minimum version of 4.6.0, so override the clang
+ * definitions to 4.6.0
+ */
+#ifdef __clang__
+    #undef __GNUC__
+    #undef __GNUC_MINOR__
+    #undef __GNUC_PATCHLEVEL__
+    #define __GNUC__ 4
+    #define __GNUC_MINOR__ 6
+    #define __GNUC_PATCHLEVEL__ 0
+#endif
+