include/linux/compiler*.h: make compiler-*.h mutually exclusive

Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
recently exposed a brittle part of the build for supporting non-gcc
compilers.

Both Clang and ICC define __GNUC__, __GNUC_MINOR__, and
__GNUC_PATCHLEVEL__ for quick compatibility with code bases that haven't
added compiler specific checks for __clang__ or __INTEL_COMPILER.

This is brittle, as they happened to get compatibility by posing as a
certain version of GCC.  This broke when upgrading the minimal version
of GCC required to build the kernel, to a version above what ICC and
Clang claim to be.

Rather than always including compiler-gcc.h then undefining or
redefining macros in compiler-intel.h or compiler-clang.h, let's
separate out the compiler specific macro definitions into mutually
exclusive headers, do more proper compiler detection, and keep shared
definitions in compiler_types.h.

Fixes: cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
Reported-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Suggested-by: Eli Friedman <efriedma@codeaurora.org>
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

9 files changed, 133 insertions, 253 deletions

diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 974d8d7d1bcd..3968d6c22455 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -38,25 +38,14 @@
 #error Sorry, your compiler targets APCS-26 but this kernel requires APCS-32
 #endif
 /*
- * GCC 3.0, 3.1: general bad code generation.
- * GCC 3.2.0: incorrect function argument offset calculation.
- * GCC 3.2.x: miscompiles NEW_AUX_ENT in fs/binfmt_elf.c
- *            (http://gcc.gnu.org/PR8896) and incorrect structure
- *	      initialisation in fs/jffs2/erase.c
  * GCC 4.8.0-4.8.2: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854
  *	      miscompiles find_get_entry(), and can result in EXT3 and EXT4
  *	      filesystem corruption (possibly other FS too).
  */
-#ifdef __GNUC__
-#if (__GNUC__ == 3 && __GNUC_MINOR__ < 3)
-#error Your compiler is too buggy; it is known to miscompile kernels.
-#error    Known good compilers: 3.3, 4.x
-#endif
-#if GCC_VERSION >= 40800 && GCC_VERSION < 40803
+#if defined(GCC_VERSION) && GCC_VERSION >= 40800 && GCC_VERSION < 40803
 #error Your compiler is too buggy; it is known to miscompile kernels
 #error and result in filesystem corruption and oopses.
 #endif
-#endif
 
 int main(void)
 {
diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index 00165ad55fb3..395dd2511568 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -43,7 +43,7 @@
 #define MISSING_CASE(x) WARN(1, "Missing case (%s == %ld)\n", \
 			     __stringify(x), (long)(x))
 
-#if GCC_VERSION >= 70000
+#if defined(GCC_VERSION) && GCC_VERSION >= 70000
 #define add_overflows(A, B) \
 	__builtin_add_overflow_p((A), (B), (typeof((A) + (B)))0)
 #else
diff --git a/drivers/watchdog/kempld_wdt.c b/drivers/watchdog/kempld_wdt.c
index 2f3b049ea301..e268add43010 100644
--- a/drivers/watchdog/kempld_wdt.c
+++ b/drivers/watchdog/kempld_wdt.c
@@ -146,12 +146,7 @@ static int kempld_wdt_set_stage_timeout(struct kempld_wdt_data *wdt_data,
 	u32 remainder;
 	u8 stage_cfg;
 
-#if GCC_VERSION < 40400
-	/* work around a bug compiling do_div() */
-	prescaler = READ_ONCE(kempld_prescaler[PRESCALER_21]);
-#else
 	prescaler = kempld_prescaler[PRESCALER_21];
-#endif
 
 	if (!stage)
 		return -EINVAL;
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 7087446c24c8..b1ce500fe8b3 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -6,11 +6,7 @@
 /* Some compiler specific definitions are overwritten here
  * for Clang compiler
  */
-
-#ifdef uninitialized_var
-#undef uninitialized_var
 #define uninitialized_var(x) x = *(&(x))
-#endif
 
 /* same as gcc, this was present in clang-2.6 so we can assume it works
  * with any version that can compile the kernel
@@ -25,14 +21,8 @@
 #define __SANITIZE_ADDRESS__
 #endif
 
-#undef __no_sanitize_address
 #define __no_sanitize_address __attribute__((no_sanitize("address")))
 
-/* Clang doesn't have a way to turn it off per-function, yet. */
-#ifdef __noretpoline
-#undef __noretpoline
-#endif
-
 /*
  * Not all versions of clang implement the the type-generic versions
  * of the builtin overflow checkers. Fortunately, clang implements
@@ -40,9 +30,17 @@
  * checks. Unfortunately, we don't know which version of gcc clang
  * pretends to be, so the macro may or may not be defined.
  */
-#undef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
 #if __has_builtin(__builtin_mul_overflow) && \
     __has_builtin(__builtin_add_overflow) && \
     __has_builtin(__builtin_sub_overflow)
 #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
 #endif
+
+/* The following are for compatibility with GCC, from compiler-gcc.h,
+ * and may be redefined here because they should not be shared with other
+ * compilers, like ICC.
+ */
+#define barrier() __asm__ __volatile__("" : : : "memory")
+#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
+#define __assume_aligned(a, ...)	\
+	__attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 250b9b7cfd60..763bbad1e258 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -75,48 +75,6 @@
 #define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 #endif
 
-/*
- * Feature detection for gnu_inline (gnu89 extern inline semantics). Either
- * __GNUC_STDC_INLINE__ is defined (not using gnu89 extern inline semantics,
- * and we opt in to the gnu89 semantics), or __GNUC_STDC_INLINE__ is not
- * defined so the gnu89 semantics are the default.
- */
-#ifdef __GNUC_STDC_INLINE__
-# define __gnu_inline	__attribute__((gnu_inline))
-#else
-# define __gnu_inline
-#endif
-
-/*
- * Force always-inline if the user requests it so via the .config,
- * or if gcc is too old.
- * GCC does not warn about unused static inline functions for
- * -Wunused-function.  This turns out to avoid the need for complex #ifdef
- * directives.  Suppress the warning in clang as well by using "unused"
- * function attribute, which is redundant but not harmful for gcc.
- * Prefer gnu_inline, so that extern inline functions do not emit an
- * externally visible function. This makes extern inline behave as per gnu89
- * semantics rather than c99. This prevents multiple symbol definition errors
- * of extern inline functions at link time.
- * A lot of inline functions can cause havoc with function tracing.
- */
-#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||		\
-    !defined(CONFIG_OPTIMIZE_INLINING)
-#define inline \
-	inline __attribute__((always_inline, unused)) notrace __gnu_inline
-#else
-#define inline inline		__attribute__((unused)) notrace __gnu_inline
-#endif
-
-#define __inline__ inline
-#define __inline inline
-#define __always_inline	inline __attribute__((always_inline))
-#define  noinline	__attribute__((noinline))
-
-#define __packed	__attribute__((packed))
-#define __weak		__attribute__((weak))
-#define __alias(symbol)	__attribute__((alias(#symbol)))
-
 #ifdef RETPOLINE
 #define __noretpoline __attribute__((indirect_branch("keep")))
 #endif
@@ -135,55 +93,9 @@
  */
 #define __naked		__attribute__((naked)) noinline __noclone notrace
 
-#define __noreturn	__attribute__((noreturn))
-
-/*
- * From the GCC manual:
- *
- * Many functions have no effects except the return value and their
- * return value depends only on the parameters and/or global
- * variables.  Such a function can be subject to common subexpression
- * elimination and loop optimization just as an arithmetic operator
- * would be.
- * [...]
- */
-#define __pure			__attribute__((pure))
-#define __aligned(x)		__attribute__((aligned(x)))
-#define __aligned_largest	__attribute__((aligned))
-#define __printf(a, b)		__attribute__((format(printf, a, b)))
-#define __scanf(a, b)		__attribute__((format(scanf, a, b)))
-#define __attribute_const__	__attribute__((__const__))
-#define __maybe_unused		__attribute__((unused))
-#define __always_unused		__attribute__((unused))
-#define __mode(x)               __attribute__((mode(x)))
-
-#define __must_check		__attribute__((warn_unused_result))
-#define __malloc		__attribute__((__malloc__))
-
-#define __used			__attribute__((__used__))
-#define __compiler_offsetof(a, b)					\
-	__builtin_offsetof(a, b)
-
-/* Mark functions as cold. gcc will assume any path leading to a call
- * to them will be unlikely.  This means a lot of manual unlikely()s
- * are unnecessary now for any paths leading to the usual suspects
- * like BUG(), printk(), panic() etc. [but let's keep them for now for
- * older compilers]
- *
- * Early snapshots of gcc 4.3 don't support this and we can't detect this
- * in the preprocessor, but we can live with this because they're unreleased.
- * Maketime probing would be overkill here.
- *
- * gcc also has a __attribute__((__hot__)) to move hot functions into
- * a special section, but I don't see any sense in this right now in
- * the kernel context
- */
-#define __cold			__attribute__((__cold__))
-
 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 
 #define __optimize(level)	__attribute__((__optimize__(level)))
-#define __nostackprotector	__optimize("no-stack-protector")
 
 #define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 
diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index 547cdc920a3c..4c7f9befa9f6 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -14,10 +14,6 @@
 /* Intel ECC compiler doesn't support gcc specific asm stmts.
  * It uses intrinsics to do the equivalent things.
  */
-#undef barrier
-#undef barrier_data
-#undef RELOC_HIDE
-#undef OPTIMIZER_HIDE_VAR
 
 #define barrier() __memory_barrier()
 #define barrier_data(ptr) barrier()
@@ -38,13 +34,12 @@
 
 #endif
 
-#ifndef __HAVE_BUILTIN_BSWAP16__
 /* icc has this, but it's called _bswap16 */
 #define __HAVE_BUILTIN_BSWAP16__
 #define __builtin_bswap16 _bswap16
-#endif
 
-/*
- * icc defines __GNUC__, but does not implement the builtin overflow checkers.
+/* The following are for compatibility with GCC, from compiler-gcc.h,
+ * and may be redefined here because they should not be shared with other
+ * compilers, like clang.
  */
-#undef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
+#define __visible	__attribute__((externally_visible))
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index fbf337933fd8..90479a0f3986 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -54,32 +54,20 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 
 #ifdef __KERNEL__
 
-#ifdef __GNUC__
-#include <linux/compiler-gcc.h>
-#endif
-
-#if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__)
-#define notrace __attribute__((hotpatch(0,0)))
-#else
-#define notrace __attribute__((no_instrument_function))
-#endif
-
-/* Intel compiler defines __GNUC__. So we will overwrite implementations
- * coming from above header files here
- */
-#ifdef __INTEL_COMPILER
-# include <linux/compiler-intel.h>
-#endif
-
-/* Clang compiler defines __GNUC__. So we will overwrite implementations
- * coming from above header files here
- */
+/* Compiler specific macros. */
 #ifdef __clang__
 #include <linux/compiler-clang.h>
+#elif defined(__INTEL_COMPILER)
+#include <linux/compiler-intel.h>
+#elif defined(__GNUC__)
+/* The above compilers also define __GNUC__, so order is important here. */
+#include <linux/compiler-gcc.h>
+#else
+#error "Unknown compiler"
 #endif
 
 /*
- * Generic compiler-dependent macros required for kernel
+ * Generic compiler-independent macros required for kernel
  * build go below this comment. Actual compiler/compiler version
  * specific implementations come from the above header files
  */
@@ -106,93 +94,19 @@ struct ftrace_likely_data {
 	unsigned long			constant;
 };
 
-#endif /* __KERNEL__ */
-
-#endif /* __ASSEMBLY__ */
-
-#ifdef __KERNEL__
-
 /* Don't. Just don't. */
 #define __deprecated
 #define __deprecated_for_modules
 
-#ifndef __must_check
-#define __must_check
-#endif
-
-#ifndef CONFIG_ENABLE_MUST_CHECK
-#undef __must_check
-#define __must_check
-#endif
-
-#ifndef __malloc
-#define __malloc
-#endif
-
-/*
- * Allow us to avoid 'defined but not used' warnings on functions and data,
- * as well as force them to be emitted to the assembly file.
- *
- * As of gcc 3.4, static functions that are not marked with attribute((used))
- * may be elided from the assembly file.  As of gcc 3.4, static data not so
- * marked will not be elided, but this may change in a future gcc version.
- *
- * NOTE: Because distributions shipped with a backported unit-at-a-time
- * compiler in gcc 3.3, we must define __used to be __attribute__((used))
- * for gcc >=3.3 instead of 3.4.
- *
- * In prior versions of gcc, such functions and data would be emitted, but
- * would be warned about except with attribute((unused)).
- *
- * Mark functions that are referenced only in inline assembly as __used so
- * the code is emitted even though it appears to be unreferenced.
- */
-#ifndef __used
-# define __used			/* unimplemented */
-#endif
-
-#ifndef __maybe_unused
-# define __maybe_unused		/* unimplemented */
-#endif
-
-#ifndef __always_unused
-# define __always_unused	/* unimplemented */
-#endif
-
-#ifndef noinline
-#define noinline
-#endif
-
-/*
- * Rather then using noinline to prevent stack consumption, use
- * noinline_for_stack instead.  For documentation reasons.
- */
-#define noinline_for_stack noinline
-
-#ifndef __always_inline
-#define __always_inline inline
-#endif
-
 #endif /* __KERNEL__ */
 
+#endif /* __ASSEMBLY__ */
+
 /*
- * From the GCC manual:
- *
- * Many functions do not examine any values except their arguments,
- * and have no effects except the return value.  Basically this is
- * just slightly more strict class than the `pure' attribute above,
- * since function is not allowed to read global memory.
- *
- * Note that a function that has pointer arguments and examines the
- * data pointed to must _not_ be declared `const'.  Likewise, a
- * function that calls a non-`const' function usually must not be
- * `const'.  It does not make sense for a `const' function to return
- * `void'.
+ * The below symbols may be defined for one or more, but not ALL, of the above
+ * compilers. We don't consider that to be an error, so set them to nothing.
+ * For example, some of them are for compiler specific plugins.
  */
-#ifndef __attribute_const__
-# define __attribute_const__	/* unimplemented */
-#endif
-
 #ifndef __designated_init
 # define __designated_init
 #endif
@@ -214,28 +128,10 @@ struct ftrace_likely_data {
 # define randomized_struct_fields_end
 #endif
 
-/*
- * Tell gcc if a function is cold. The compiler will assume any path
- * directly leading to the call is unlikely.
- */
-
-#ifndef __cold
-#define __cold
-#endif
-
-/* Simple shorthand for a section definition */
-#ifndef __section
-# define __section(S) __attribute__ ((__section__(#S)))
-#endif
-
 #ifndef __visible
 #define __visible
 #endif
 
-#ifndef __nostackprotector
-# define __nostackprotector
-#endif
-
 /*
  * Assume alignment of return value.
  */
@@ -243,17 +139,23 @@ struct ftrace_likely_data {
 #define __assume_aligned(a, ...)
 #endif
 
-
 /* Are two types/vars the same type (ignoring qualifiers)? */
-#ifndef __same_type
-# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
-#endif
+#define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 
 /* Is this type a native word size -- useful for atomic operations */
-#ifndef __native_word
-# define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
+#define __native_word(t) \
+	(sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \
+	 sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
+
+#ifndef __attribute_const__
+#define __attribute_const__	__attribute__((__const__))
 #endif
 
+#ifndef __noclone
+#define __noclone
+#endif
+
+/* Helpers for emitting diagnostics in pragmas. */
 #ifndef __diag
 #define __diag(string)
 #endif
@@ -272,4 +174,92 @@ struct ftrace_likely_data {
 #define __diag_error(compiler, version, option, comment) \
 	__diag_ ## compiler(version, error, option)
 
+/*
+ * From the GCC manual:
+ *
+ * Many functions have no effects except the return value and their
+ * return value depends only on the parameters and/or global
+ * variables.  Such a function can be subject to common subexpression
+ * elimination and loop optimization just as an arithmetic operator
+ * would be.
+ * [...]
+ */
+#define __pure			__attribute__((pure))
+#define __aligned(x)		__attribute__((aligned(x)))
+#define __aligned_largest	__attribute__((aligned))
+#define __printf(a, b)		__attribute__((format(printf, a, b)))
+#define __scanf(a, b)		__attribute__((format(scanf, a, b)))
+#define __maybe_unused		__attribute__((unused))
+#define __always_unused		__attribute__((unused))
+#define __mode(x)		__attribute__((mode(x)))
+#define __malloc		__attribute__((__malloc__))
+#define __used			__attribute__((__used__))
+#define __noreturn		__attribute__((noreturn))
+#define __packed		__attribute__((packed))
+#define __weak			__attribute__((weak))
+#define __alias(symbol)		__attribute__((alias(#symbol)))
+#define __cold			__attribute__((cold))
+#define __section(S)		__attribute__((__section__(#S)))
+
+
+#ifdef CONFIG_ENABLE_MUST_CHECK
+#define __must_check		__attribute__((warn_unused_result))
+#else
+#define __must_check
+#endif
+
+#if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__)
+#define notrace			__attribute__((hotpatch(0, 0)))
+#else
+#define notrace			__attribute__((no_instrument_function))
+#endif
+
+#define __compiler_offsetof(a, b)	__builtin_offsetof(a, b)
+
+/*
+ * Feature detection for gnu_inline (gnu89 extern inline semantics). Either
+ * __GNUC_STDC_INLINE__ is defined (not using gnu89 extern inline semantics,
+ * and we opt in to the gnu89 semantics), or __GNUC_STDC_INLINE__ is not
+ * defined so the gnu89 semantics are the default.
+ */
+#ifdef __GNUC_STDC_INLINE__
+# define __gnu_inline	__attribute__((gnu_inline))
+#else
+# define __gnu_inline
+#endif
+
+/*
+ * Force always-inline if the user requests it so via the .config.
+ * GCC does not warn about unused static inline functions for
+ * -Wunused-function.  This turns out to avoid the need for complex #ifdef
+ * directives.  Suppress the warning in clang as well by using "unused"
+ * function attribute, which is redundant but not harmful for gcc.
+ * Prefer gnu_inline, so that extern inline functions do not emit an
+ * externally visible function. This makes extern inline behave as per gnu89
+ * semantics rather than c99. This prevents multiple symbol definition errors
+ * of extern inline functions at link time.
+ * A lot of inline functions can cause havoc with function tracing.
+ */
+#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
+	!defined(CONFIG_OPTIMIZE_INLINING)
+#define inline \
+	inline __attribute__((always_inline, unused)) notrace __gnu_inline
+#else
+#define inline inline	__attribute__((unused)) notrace __gnu_inline
+#endif
+
+#define __inline__ inline
+#define __inline inline
+#define noinline	__attribute__((noinline))
+
+#ifndef __always_inline
+#define __always_inline inline __attribute__((always_inline))
+#endif
+
+/*
+ * Rather then using noinline to prevent stack consumption, use
+ * noinline_for_stack instead.  For documentation reasons.
+ */
+#define noinline_for_stack noinline
+
 #endif /* __LINUX_COMPILER_TYPES_H */
diff --git a/mm/ksm.c b/mm/ksm.c
index 1bd514c9e5d0..5b0894b45ee5 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -652,9 +652,9 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
 	 * list_head to stay clear from the rb_parent_color union
 	 * (aligned and different than any node) and also different
 	 * from &migrate_nodes. This will verify that future list.h changes
-	 * don't break STABLE_NODE_DUP_HEAD.
+	 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
 	 */
-#if GCC_VERSION >= 40903 /* only recent gcc can handle it */
+#if defined(GCC_VERSION) && GCC_VERSION >= 40903
 	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
 	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
 #endif
diff --git a/mm/migrate.c b/mm/migrate.c
index 4a83268e23c2..c27e97b5b69d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1131,7 +1131,8 @@ out:
  * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
  * around it.
  */
-#if (GCC_VERSION >= 40700 && GCC_VERSION < 40900) && defined(CONFIG_ARM)
+#if defined(CONFIG_ARM) && \
+	defined(GCC_VERSION) && GCC_VERSION < 40900 && GCC_VERSION >= 40700
 #define ICE_noinline noinline
 #else
 #define ICE_noinline