llvm/libc/src/sys/auxv/linux/getauxval.cpp

//===-- Implementation file for getauxval function --------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "src/sys/auxv/getauxval.h"
#include "config/app.h"
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
#include "src/errno/libc_errno.h"
#include <linux/auxvec.h>

// for guarded initialization
#include "src/__support/threads/callonce.h"
#include "src/__support/threads/linux/futex_word.h"

// for mallocing the global auxv
#include "src/sys/mman/mmap.h"
#include "src/sys/mman/munmap.h"

// for reading /proc/self/auxv
#include "src/fcntl/open.h"
#include "src/sys/prctl/prctl.h"
#include "src/unistd/close.h"
#include "src/unistd/read.h"

// getauxval will work either with or without __cxa_atexit support.
// In order to detect if __cxa_atexit is supported, we define a weak symbol.
// We prefer __cxa_atexit as it is always defined as a C symbol whileas atexit
// may not be created via objcopy yet. Also, for glibc, atexit is provided via
// libc_nonshared.a rather than libc.so. So, it is may not be made ready for
// overlay builds.
extern "C" [[gnu::weak]] int __cxa_atexit(void (*callback)(void *),
                                          void *payload, void *);

namespace LIBC_NAMESPACE_DECL {

constexpr static size_t MAX_AUXV_ENTRIES = …;

// Helper to recover or set errno
class AuxvErrnoGuard { … };

// Helper to manage the memory
static AuxEntry *auxv = …;

class AuxvMMapGuard { … };

class AuxvFdGuard { … };

static void initialize_auxv_once(void) { … }

static AuxEntry read_entry(int fd) { … }

LLVM_LIBC_FUNCTION(unsigned long, getauxval, (unsigned long id)) { … }
} // namespace LIBC_NAMESPACE_DECL