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8634de6d25
gcc support for __builtin_bswap16() was supposedly added for powerpc in
gcc 4.6, and was then later added for other architectures in gcc 4.8.
However, Stephen Rothwell reported that attempting to use it on powerpc
in gcc 4.6 fails with:
lib/vsprintf.c:160:2: error: initializer element is not constant
lib/vsprintf.c:160:2: error: (near initialization for 'decpair[0]')
lib/vsprintf.c:160:2: error: initializer element is not constant
lib/vsprintf.c:160:2: error: (near initialization for 'decpair[1]')
...
I'm not entirely sure what those errors mean, but I don't see them on
gcc 4.8. So let's consider gcc 4.8 to be the official starting point
for __builtin_bswap16().
Arnd Bergmann adds:
"I found the commit in gcc-4.8 that replaced the powerpc-specific
implementation of __builtin_bswap16 with an architecture-independent
one. Apparently the powerpc version (gcc-4.6 and 4.7) just mapped to
the lhbrx/sthbrx instructions, so it ended up not being a constant,
though the intent of the patch was mainly to add support for the
builtin to x86:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52624
has the patch that went into gcc-4.8 and more information."
Fixes: 7322dd755e ("byteswap: try to avoid __builtin_constant_p gcc bug")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
284 lines
9.5 KiB
C
284 lines
9.5 KiB
C
#ifndef __LINUX_COMPILER_H
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#error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
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#endif
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/*
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* Common definitions for all gcc versions go here.
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*/
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#define GCC_VERSION (__GNUC__ * 10000 \
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+ __GNUC_MINOR__ * 100 \
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+ __GNUC_PATCHLEVEL__)
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/* Optimization barrier */
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/* The "volatile" is due to gcc bugs */
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#define barrier() __asm__ __volatile__("": : :"memory")
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/*
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* This version is i.e. to prevent dead stores elimination on @ptr
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* where gcc and llvm may behave differently when otherwise using
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* normal barrier(): while gcc behavior gets along with a normal
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* barrier(), llvm needs an explicit input variable to be assumed
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* clobbered. The issue is as follows: while the inline asm might
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* access any memory it wants, the compiler could have fit all of
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* @ptr into memory registers instead, and since @ptr never escaped
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* from that, it proofed that the inline asm wasn't touching any of
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* it. This version works well with both compilers, i.e. we're telling
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* the compiler that the inline asm absolutely may see the contents
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* of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
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*/
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#define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
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/*
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* This macro obfuscates arithmetic on a variable address so that gcc
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* shouldn't recognize the original var, and make assumptions about it.
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*
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* This is needed because the C standard makes it undefined to do
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* pointer arithmetic on "objects" outside their boundaries and the
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* gcc optimizers assume this is the case. In particular they
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* assume such arithmetic does not wrap.
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*
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* A miscompilation has been observed because of this on PPC.
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* To work around it we hide the relationship of the pointer and the object
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* using this macro.
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*
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* Versions of the ppc64 compiler before 4.1 had a bug where use of
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* RELOC_HIDE could trash r30. The bug can be worked around by changing
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* the inline assembly constraint from =g to =r, in this particular
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* case either is valid.
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*/
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#define RELOC_HIDE(ptr, off) \
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({ \
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unsigned long __ptr; \
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__asm__ ("" : "=r"(__ptr) : "0"(ptr)); \
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(typeof(ptr)) (__ptr + (off)); \
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})
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/* Make the optimizer believe the variable can be manipulated arbitrarily. */
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#define OPTIMIZER_HIDE_VAR(var) \
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__asm__ ("" : "=r" (var) : "0" (var))
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#ifdef __CHECKER__
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#define __must_be_array(a) 0
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#else
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/* &a[0] degrades to a pointer: a different type from an array */
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#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
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#endif
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/*
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* Force always-inline if the user requests it so via the .config,
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* or if gcc is too old:
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*/
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#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
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!defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
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#define inline inline __attribute__((always_inline)) notrace
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#define __inline__ __inline__ __attribute__((always_inline)) notrace
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#define __inline __inline __attribute__((always_inline)) notrace
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#else
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/* A lot of inline functions can cause havoc with function tracing */
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#define inline inline notrace
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#define __inline__ __inline__ notrace
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#define __inline __inline notrace
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#endif
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#define __always_inline inline __attribute__((always_inline))
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#define noinline __attribute__((noinline))
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#define __deprecated __attribute__((deprecated))
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#define __packed __attribute__((packed))
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#define __weak __attribute__((weak))
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#define __alias(symbol) __attribute__((alias(#symbol)))
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/*
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* it doesn't make sense on ARM (currently the only user of __naked)
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* to trace naked functions because then mcount is called without
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* stack and frame pointer being set up and there is no chance to
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* restore the lr register to the value before mcount was called.
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*
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* The asm() bodies of naked functions often depend on standard calling
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* conventions, therefore they must be noinline and noclone.
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*
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* GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
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* See GCC PR44290.
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*/
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#define __naked __attribute__((naked)) noinline __noclone notrace
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#define __noreturn __attribute__((noreturn))
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/*
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* From the GCC manual:
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*
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* Many functions have no effects except the return value and their
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* return value depends only on the parameters and/or global
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* variables. Such a function can be subject to common subexpression
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* elimination and loop optimization just as an arithmetic operator
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* would be.
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* [...]
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*/
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#define __pure __attribute__((pure))
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#define __aligned(x) __attribute__((aligned(x)))
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#define __printf(a, b) __attribute__((format(printf, a, b)))
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#define __scanf(a, b) __attribute__((format(scanf, a, b)))
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#define __attribute_const__ __attribute__((__const__))
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#define __maybe_unused __attribute__((unused))
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#define __always_unused __attribute__((unused))
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/* gcc version specific checks */
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#if GCC_VERSION < 30200
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# error Sorry, your compiler is too old - please upgrade it.
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#endif
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#if GCC_VERSION < 30300
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# define __used __attribute__((__unused__))
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#else
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# define __used __attribute__((__used__))
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#endif
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#ifdef CONFIG_GCOV_KERNEL
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# if GCC_VERSION < 30400
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# error "GCOV profiling support for gcc versions below 3.4 not included"
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# endif /* __GNUC_MINOR__ */
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#endif /* CONFIG_GCOV_KERNEL */
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#if GCC_VERSION >= 30400
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#define __must_check __attribute__((warn_unused_result))
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#endif
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#if GCC_VERSION >= 40000
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/* GCC 4.1.[01] miscompiles __weak */
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#ifdef __KERNEL__
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# if GCC_VERSION >= 40100 && GCC_VERSION <= 40101
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# error Your version of gcc miscompiles the __weak directive
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# endif
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#endif
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#define __used __attribute__((__used__))
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#define __compiler_offsetof(a, b) \
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__builtin_offsetof(a, b)
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#if GCC_VERSION >= 40100 && GCC_VERSION < 40600
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# define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
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#endif
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#if GCC_VERSION >= 40300
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/* Mark functions as cold. gcc will assume any path leading to a call
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* to them will be unlikely. This means a lot of manual unlikely()s
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* are unnecessary now for any paths leading to the usual suspects
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* like BUG(), printk(), panic() etc. [but let's keep them for now for
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* older compilers]
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*
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* Early snapshots of gcc 4.3 don't support this and we can't detect this
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* in the preprocessor, but we can live with this because they're unreleased.
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* Maketime probing would be overkill here.
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*
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* gcc also has a __attribute__((__hot__)) to move hot functions into
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* a special section, but I don't see any sense in this right now in
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* the kernel context
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*/
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#define __cold __attribute__((__cold__))
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#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
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#ifndef __CHECKER__
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# define __compiletime_warning(message) __attribute__((warning(message)))
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# define __compiletime_error(message) __attribute__((error(message)))
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#endif /* __CHECKER__ */
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#endif /* GCC_VERSION >= 40300 */
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#if GCC_VERSION >= 40500
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/*
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* Mark a position in code as unreachable. This can be used to
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* suppress control flow warnings after asm blocks that transfer
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* control elsewhere.
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*
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* Early snapshots of gcc 4.5 don't support this and we can't detect
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* this in the preprocessor, but we can live with this because they're
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* unreleased. Really, we need to have autoconf for the kernel.
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*/
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#define unreachable() __builtin_unreachable()
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/* Mark a function definition as prohibited from being cloned. */
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#define __noclone __attribute__((__noclone__, __optimize__("no-tracer")))
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#endif /* GCC_VERSION >= 40500 */
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#if GCC_VERSION >= 40600
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/*
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* When used with Link Time Optimization, gcc can optimize away C functions or
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* variables which are referenced only from assembly code. __visible tells the
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* optimizer that something else uses this function or variable, thus preventing
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* this.
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*/
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#define __visible __attribute__((externally_visible))
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#endif
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#if GCC_VERSION >= 40900 && !defined(__CHECKER__)
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/*
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* __assume_aligned(n, k): Tell the optimizer that the returned
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* pointer can be assumed to be k modulo n. The second argument is
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* optional (default 0), so we use a variadic macro to make the
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* shorthand.
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*
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* Beware: Do not apply this to functions which may return
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* ERR_PTRs. Also, it is probably unwise to apply it to functions
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* returning extra information in the low bits (but in that case the
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* compiler should see some alignment anyway, when the return value is
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* massaged by 'flags = ptr & 3; ptr &= ~3;').
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*/
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#define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
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#endif
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/*
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* GCC 'asm goto' miscompiles certain code sequences:
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*
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* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
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*
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* Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
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*
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* (asm goto is automatically volatile - the naming reflects this.)
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*/
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#define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
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#ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
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#if GCC_VERSION >= 40400
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#define __HAVE_BUILTIN_BSWAP32__
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#define __HAVE_BUILTIN_BSWAP64__
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#endif
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#if GCC_VERSION >= 40800
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#define __HAVE_BUILTIN_BSWAP16__
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#endif
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#endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
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#if GCC_VERSION >= 50000
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#define KASAN_ABI_VERSION 4
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#elif GCC_VERSION >= 40902
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#define KASAN_ABI_VERSION 3
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#endif
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#if GCC_VERSION >= 40902
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/*
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* Tell the compiler that address safety instrumentation (KASAN)
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* should not be applied to that function.
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* Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
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*/
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#define __no_sanitize_address __attribute__((no_sanitize_address))
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#endif
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#endif /* gcc version >= 40000 specific checks */
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#if !defined(__noclone)
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#define __noclone /* not needed */
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#endif
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#if !defined(__no_sanitize_address)
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#define __no_sanitize_address
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#endif
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/*
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* A trick to suppress uninitialized variable warning without generating any
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* code
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*/
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#define uninitialized_var(x) x = x
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