
- CONSTINIT and constexpr are not compatible in C++20 - base::Features should not be declared constexpr - Move the background details for LOGICALLY_CONST to the compiler_specific.h header. Bug: 1364289 Change-Id: I74843e1ccb1cab04914bd50bc4f61ab80814a4e4 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3900070 Reviewed-by: Joe Mason <joenotcharles@google.com> Commit-Queue: Alexei Svitkine <asvitkine@chromium.org> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org> Cr-Commit-Position: refs/heads/main@{#1047817}
423 lines
15 KiB
C++
423 lines
15 KiB
C++
// Copyright 2012 The Chromium Authors
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_COMPILER_SPECIFIC_H_
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#define BASE_COMPILER_SPECIFIC_H_
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#include "build/build_config.h"
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#if defined(COMPILER_MSVC) && !defined(__clang__)
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#error "Only clang-cl is supported on Windows, see https://crbug.com/988071"
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#endif
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// This is a wrapper around `__has_cpp_attribute`, which can be used to test for
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// the presence of an attribute. In case the compiler does not support this
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// macro it will simply evaluate to 0.
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//
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// References:
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// https://wg21.link/sd6#testing-for-the-presence-of-an-attribute-__has_cpp_attribute
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// https://wg21.link/cpp.cond#:__has_cpp_attribute
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#if defined(__has_cpp_attribute)
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#define HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
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#else
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#define HAS_CPP_ATTRIBUTE(x) 0
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#endif
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// A wrapper around `__has_attribute`, similar to HAS_CPP_ATTRIBUTE.
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#if defined(__has_attribute)
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#define HAS_ATTRIBUTE(x) __has_attribute(x)
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#else
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#define HAS_ATTRIBUTE(x) 0
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#endif
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// A wrapper around `__has_builtin`, similar to HAS_CPP_ATTRIBUTE.
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#if defined(__has_builtin)
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#define HAS_BUILTIN(x) __has_builtin(x)
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#else
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#define HAS_BUILTIN(x) 0
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#endif
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// Annotate a function indicating it should not be inlined.
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// Use like:
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// NOINLINE void DoStuff() { ... }
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#if defined(COMPILER_GCC) || defined(__clang__)
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#define NOINLINE __attribute__((noinline))
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#elif defined(COMPILER_MSVC)
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#define NOINLINE __declspec(noinline)
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#else
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#define NOINLINE
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#endif
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#if defined(COMPILER_GCC) && defined(NDEBUG)
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#define ALWAYS_INLINE inline __attribute__((__always_inline__))
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#elif defined(COMPILER_MSVC) && defined(NDEBUG)
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#define ALWAYS_INLINE __forceinline
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#else
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#define ALWAYS_INLINE inline
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#endif
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// Annotate a function indicating it should never be tail called. Useful to make
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// sure callers of the annotated function are never omitted from call-stacks.
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// To provide the complementary behavior (prevent the annotated function from
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// being omitted) look at NOINLINE. Also note that this doesn't prevent code
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// folding of multiple identical caller functions into a single signature. To
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// prevent code folding, see NO_CODE_FOLDING() in base/debug/alias.h.
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// Use like:
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// void NOT_TAIL_CALLED FooBar();
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#if defined(__clang__) && HAS_ATTRIBUTE(not_tail_called)
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#define NOT_TAIL_CALLED __attribute__((not_tail_called))
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#else
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#define NOT_TAIL_CALLED
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#endif
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// Specify memory alignment for structs, classes, etc.
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// Use like:
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// class ALIGNAS(16) MyClass { ... }
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// ALIGNAS(16) int array[4];
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//
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// In most places you can use the C++11 keyword "alignas", which is preferred.
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//
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// But compilers have trouble mixing __attribute__((...)) syntax with
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// alignas(...) syntax.
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//
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// Doesn't work in clang or gcc:
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// struct alignas(16) __attribute__((packed)) S { char c; };
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// Works in clang but not gcc:
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// struct __attribute__((packed)) alignas(16) S2 { char c; };
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// Works in clang and gcc:
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// struct alignas(16) S3 { char c; } __attribute__((packed));
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//
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// There are also some attributes that must be specified *before* a class
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// definition: visibility (used for exporting functions/classes) is one of
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// these attributes. This means that it is not possible to use alignas() with a
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// class that is marked as exported.
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#if defined(COMPILER_MSVC)
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#define ALIGNAS(byte_alignment) __declspec(align(byte_alignment))
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#elif defined(COMPILER_GCC)
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#define ALIGNAS(byte_alignment) __attribute__((aligned(byte_alignment)))
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#endif
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// In case the compiler supports it NO_UNIQUE_ADDRESS evaluates to the C++20
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// attribute [[no_unique_address]]. This allows annotating data members so that
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// they need not have an address distinct from all other non-static data members
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// of its class.
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//
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// References:
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// * https://en.cppreference.com/w/cpp/language/attributes/no_unique_address
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// * https://wg21.link/dcl.attr.nouniqueaddr
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#if HAS_CPP_ATTRIBUTE(no_unique_address)
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#define NO_UNIQUE_ADDRESS [[no_unique_address]]
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#else
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#define NO_UNIQUE_ADDRESS
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#endif
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// Tell the compiler a function is using a printf-style format string.
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// |format_param| is the one-based index of the format string parameter;
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// |dots_param| is the one-based index of the "..." parameter.
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// For v*printf functions (which take a va_list), pass 0 for dots_param.
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// (This is undocumented but matches what the system C headers do.)
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// For member functions, the implicit this parameter counts as index 1.
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#if defined(COMPILER_GCC) || defined(__clang__)
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#define PRINTF_FORMAT(format_param, dots_param) \
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__attribute__((format(printf, format_param, dots_param)))
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#else
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#define PRINTF_FORMAT(format_param, dots_param)
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#endif
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// WPRINTF_FORMAT is the same, but for wide format strings.
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// This doesn't appear to yet be implemented in any compiler.
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// See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38308 .
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#define WPRINTF_FORMAT(format_param, dots_param)
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// If available, it would look like:
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// __attribute__((format(wprintf, format_param, dots_param)))
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// Sanitizers annotations.
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#if HAS_ATTRIBUTE(no_sanitize)
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#define NO_SANITIZE(what) __attribute__((no_sanitize(what)))
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#endif
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#if !defined(NO_SANITIZE)
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#define NO_SANITIZE(what)
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#endif
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// MemorySanitizer annotations.
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#if defined(MEMORY_SANITIZER) && !BUILDFLAG(IS_NACL)
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#include <sanitizer/msan_interface.h>
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// Mark a memory region fully initialized.
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// Use this to annotate code that deliberately reads uninitialized data, for
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// example a GC scavenging root set pointers from the stack.
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#define MSAN_UNPOISON(p, size) __msan_unpoison(p, size)
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// Check a memory region for initializedness, as if it was being used here.
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// If any bits are uninitialized, crash with an MSan report.
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// Use this to sanitize data which MSan won't be able to track, e.g. before
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// passing data to another process via shared memory.
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#define MSAN_CHECK_MEM_IS_INITIALIZED(p, size) \
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__msan_check_mem_is_initialized(p, size)
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#else // MEMORY_SANITIZER
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#define MSAN_UNPOISON(p, size)
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#define MSAN_CHECK_MEM_IS_INITIALIZED(p, size)
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#endif // MEMORY_SANITIZER
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// DISABLE_CFI_PERF -- Disable Control Flow Integrity for perf reasons.
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#if !defined(DISABLE_CFI_PERF)
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#if defined(__clang__) && defined(OFFICIAL_BUILD)
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#define DISABLE_CFI_PERF __attribute__((no_sanitize("cfi")))
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#else
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#define DISABLE_CFI_PERF
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#endif
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#endif
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// DISABLE_CFI_ICALL -- Disable Control Flow Integrity indirect call checks.
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// Security Note: if you just need to allow calling of dlsym functions use
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// DISABLE_CFI_DLSYM.
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#if !defined(DISABLE_CFI_ICALL)
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#if BUILDFLAG(IS_WIN)
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// Windows also needs __declspec(guard(nocf)).
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#define DISABLE_CFI_ICALL NO_SANITIZE("cfi-icall") __declspec(guard(nocf))
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#else
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#define DISABLE_CFI_ICALL NO_SANITIZE("cfi-icall")
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#endif
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#endif
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#if !defined(DISABLE_CFI_ICALL)
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#define DISABLE_CFI_ICALL
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#endif
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// DISABLE_CFI_DLSYM -- applies DISABLE_CFI_ICALL on platforms where dlsym
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// functions must be called. Retains CFI checks on platforms where loaded
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// modules participate in CFI (e.g. Windows).
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#if !defined(DISABLE_CFI_DLSYM)
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#if BUILDFLAG(IS_WIN)
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// Windows modules register functions when loaded so can be checked by CFG.
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#define DISABLE_CFI_DLSYM
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#else
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#define DISABLE_CFI_DLSYM DISABLE_CFI_ICALL
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#endif
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#endif
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#if !defined(DISABLE_CFI_DLSYM)
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#define DISABLE_CFI_DLSYM
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#endif
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// Macro useful for writing cross-platform function pointers.
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#if !defined(CDECL)
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#if BUILDFLAG(IS_WIN)
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#define CDECL __cdecl
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#else // BUILDFLAG(IS_WIN)
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#define CDECL
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#endif // BUILDFLAG(IS_WIN)
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#endif // !defined(CDECL)
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// Macro for hinting that an expression is likely to be false.
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#if !defined(UNLIKELY)
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#if defined(COMPILER_GCC) || defined(__clang__)
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#define UNLIKELY(x) __builtin_expect(!!(x), 0)
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#else
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#define UNLIKELY(x) (x)
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#endif // defined(COMPILER_GCC)
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#endif // !defined(UNLIKELY)
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#if !defined(LIKELY)
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#if defined(COMPILER_GCC) || defined(__clang__)
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#define LIKELY(x) __builtin_expect(!!(x), 1)
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#else
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#define LIKELY(x) (x)
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#endif // defined(COMPILER_GCC)
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#endif // !defined(LIKELY)
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// Compiler feature-detection.
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// clang.llvm.org/docs/LanguageExtensions.html#has-feature-and-has-extension
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#if defined(__has_feature)
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#define HAS_FEATURE(FEATURE) __has_feature(FEATURE)
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#else
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#define HAS_FEATURE(FEATURE) 0
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#endif
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#if defined(COMPILER_GCC)
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#define PRETTY_FUNCTION __PRETTY_FUNCTION__
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#elif defined(COMPILER_MSVC)
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#define PRETTY_FUNCTION __FUNCSIG__
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#else
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// See https://en.cppreference.com/w/c/language/function_definition#func
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#define PRETTY_FUNCTION __func__
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#endif
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#if !defined(CPU_ARM_NEON)
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#if defined(__arm__)
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#if !defined(__ARMEB__) && !defined(__ARM_EABI__) && !defined(__EABI__) && \
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!defined(__VFP_FP__) && !defined(_WIN32_WCE) && !defined(ANDROID)
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#error Chromium does not support middle endian architecture
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#endif
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#if defined(__ARM_NEON__)
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#define CPU_ARM_NEON 1
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#endif
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#endif // defined(__arm__)
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#endif // !defined(CPU_ARM_NEON)
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#if !defined(HAVE_MIPS_MSA_INTRINSICS)
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#if defined(__mips_msa) && defined(__mips_isa_rev) && (__mips_isa_rev >= 5)
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#define HAVE_MIPS_MSA_INTRINSICS 1
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#endif
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#endif
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#if defined(__clang__) && HAS_ATTRIBUTE(uninitialized)
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// Attribute "uninitialized" disables -ftrivial-auto-var-init=pattern for
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// the specified variable.
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// Library-wide alternative is
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// 'configs -= [ "//build/config/compiler:default_init_stack_vars" ]' in .gn
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// file.
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//
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// See "init_stack_vars" in build/config/compiler/BUILD.gn and
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// http://crbug.com/977230
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// "init_stack_vars" is enabled for non-official builds and we hope to enable it
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// in official build in 2020 as well. The flag writes fixed pattern into
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// uninitialized parts of all local variables. In rare cases such initialization
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// is undesirable and attribute can be used:
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// 1. Degraded performance
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// In most cases compiler is able to remove additional stores. E.g. if memory is
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// never accessed or properly initialized later. Preserved stores mostly will
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// not affect program performance. However if compiler failed on some
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// performance critical code we can get a visible regression in a benchmark.
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// 2. memset, memcpy calls
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// Compiler may replaces some memory writes with memset or memcpy calls. This is
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// not -ftrivial-auto-var-init specific, but it can happen more likely with the
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// flag. It can be a problem if code is not linked with C run-time library.
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//
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// Note: The flag is security risk mitigation feature. So in future the
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// attribute uses should be avoided when possible. However to enable this
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// mitigation on the most of the code we need to be less strict now and minimize
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// number of exceptions later. So if in doubt feel free to use attribute, but
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// please document the problem for someone who is going to cleanup it later.
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// E.g. platform, bot, benchmark or test name in patch description or next to
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// the attribute.
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#define STACK_UNINITIALIZED __attribute__((uninitialized))
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#else
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#define STACK_UNINITIALIZED
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#endif
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// Attribute "no_stack_protector" disables -fstack-protector for the specified
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// function.
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//
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// "stack_protector" is enabled on most POSIX builds. The flag adds a canary
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// to each stack frame, which on function return is checked against a reference
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// canary. If the canaries do not match, it's likely that a stack buffer
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// overflow has occurred, so immediately crashing will prevent exploitation in
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// many cases.
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//
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// In some cases it's desirable to remove this, e.g. on hot functions, or if
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// we have purposely changed the reference canary.
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#if defined(COMPILER_GCC) || defined(__clang__)
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#if HAS_ATTRIBUTE(__no_stack_protector__)
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#define NO_STACK_PROTECTOR __attribute__((__no_stack_protector__))
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#else
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#define NO_STACK_PROTECTOR __attribute__((__optimize__("-fno-stack-protector")))
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#endif
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#else
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#define NO_STACK_PROTECTOR
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#endif
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// The ANALYZER_ASSUME_TRUE(bool arg) macro adds compiler-specific hints
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// to Clang which control what code paths are statically analyzed,
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// and is meant to be used in conjunction with assert & assert-like functions.
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// The expression is passed straight through if analysis isn't enabled.
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//
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// ANALYZER_SKIP_THIS_PATH() suppresses static analysis for the current
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// codepath and any other branching codepaths that might follow.
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#if defined(__clang_analyzer__)
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inline constexpr bool AnalyzerNoReturn() __attribute__((analyzer_noreturn)) {
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return false;
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}
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inline constexpr bool AnalyzerAssumeTrue(bool arg) {
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// AnalyzerNoReturn() is invoked and analysis is terminated if |arg| is
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// false.
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return arg || AnalyzerNoReturn();
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}
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#define ANALYZER_ASSUME_TRUE(arg) ::AnalyzerAssumeTrue(!!(arg))
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#define ANALYZER_SKIP_THIS_PATH() static_cast<void>(::AnalyzerNoReturn())
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#else // !defined(__clang_analyzer__)
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#define ANALYZER_ASSUME_TRUE(arg) (arg)
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#define ANALYZER_SKIP_THIS_PATH()
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#endif // defined(__clang_analyzer__)
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// Use nomerge attribute to disable optimization of merging multiple same calls.
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#if defined(__clang__) && HAS_ATTRIBUTE(nomerge)
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#define NOMERGE [[clang::nomerge]]
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#else
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#define NOMERGE
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#endif
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// Marks a type as being eligible for the "trivial" ABI despite having a
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// non-trivial destructor or copy/move constructor. Such types can be relocated
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// after construction by simply copying their memory, which makes them eligible
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// to be passed in registers. The canonical example is std::unique_ptr.
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//
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// Use with caution; this has some subtle effects on constructor/destructor
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// ordering and will be very incorrect if the type relies on its address
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// remaining constant. When used as a function argument (by value), the value
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// may be constructed in the caller's stack frame, passed in a register, and
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// then used and destructed in the callee's stack frame. A similar thing can
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// occur when values are returned.
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//
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// TRIVIAL_ABI is not needed for types which have a trivial destructor and
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// copy/move constructors, such as base::TimeTicks and other POD.
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//
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// It is also not likely to be effective on types too large to be passed in one
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// or two registers on typical target ABIs.
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//
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// See also:
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// https://clang.llvm.org/docs/AttributeReference.html#trivial-abi
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// https://libcxx.llvm.org/docs/DesignDocs/UniquePtrTrivialAbi.html
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#if defined(__clang__) && HAS_ATTRIBUTE(trivial_abi)
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#define TRIVIAL_ABI [[clang::trivial_abi]]
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#else
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#define TRIVIAL_ABI
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#endif
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// Marks a member function as reinitializing a moved-from variable.
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// See also
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// https://clang.llvm.org/extra/clang-tidy/checks/bugprone-use-after-move.html#reinitialization
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#if defined(__clang__) && HAS_ATTRIBUTE(reinitializes)
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#define REINITIALIZES_AFTER_MOVE [[clang::reinitializes]]
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#else
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#define REINITIALIZES_AFTER_MOVE
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#endif
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// Requires constant initialization. See constinit in C++20. Allows to rely on a
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// variable being initialized before execution, and not requiring a global
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// constructor.
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#if HAS_ATTRIBUTE(require_constant_initialization)
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#define CONSTINIT __attribute__((require_constant_initialization))
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#endif
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#if !defined(CONSTINIT)
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#define CONSTINIT
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#endif
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#if defined(__clang__)
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#define GSL_OWNER [[gsl::Owner]]
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#define GSL_POINTER [[gsl::Pointer]]
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#else
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#define GSL_OWNER
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#define GSL_POINTER
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#endif
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// Adds the "logically_const" tag to a symbol's mangled name. The "Mutable
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// Constants" check [1] detects instances of constants that aren't in .rodata,
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// e.g. due to a missing `const`. Using this tag suppresses the check for this
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// symbol, allowing it to live outside .rodata without a warning.
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//
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// [1]:
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// https://crsrc.org/c/docs/speed/binary_size/android_binary_size_trybot.md#Mutable-Constants
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#if defined(COMPILER_GCC) || defined(__clang__)
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#define LOGICALLY_CONST [[gnu::abi_tag("logically_const")]]
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#else
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#define LOGICALLY_CONST
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#endif
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#endif // BASE_COMPILER_SPECIFIC_H_
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