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

Commit cafa001 ("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: cafa001 ("Raise the minimum required gcc version to 4.6")
Reported-by: Masahiro Yamada <[email protected]>
Suggested-by: Eli Friedman <[email protected]>
Suggested-by: Joe Perches <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: nickdesaulniers

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)
 {

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

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;

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
@@ -25,24 +21,26 @@
 #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
  * __has_builtin allowing us to avoid awkward version
  * 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__)))

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)
 

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))