77 lines
2.4 KiB
C
77 lines
2.4 KiB
C
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/*
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* Copyright (C) 2013 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef KERNEL_ARGUMENT_BLOCK_H
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#define KERNEL_ARGUMENT_BLOCK_H
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#include <elf.h>
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#include <stdint.h>
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#include <sys/auxv.h>
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// When the kernel starts the dynamic linker, it passes a pointer to a block
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// of memory containing argc, the argv array, the environment variable array,
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// and the array of ELF aux vectors. This class breaks that block up into its
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// constituents for easy access.
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class KernelArgumentBlock {
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public:
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KernelArgumentBlock(void* raw_args) {
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uint32_t* args = reinterpret_cast<uint32_t*>(raw_args);
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argc = static_cast<int>(*args);
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argv = reinterpret_cast<char**>(args + 1);
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envp = argv + argc + 1;
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// Skip over all environment variable definitions to find aux vector.
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// The end of the environment block is marked by two NULL pointers.
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char** p = envp;
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while (*p != NULL) {
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++p;
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}
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++p; // Skip second NULL;
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auxv = reinterpret_cast<Elf32_auxv_t*>(p);
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}
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// Similar to ::getauxval but doesn't require the libc global variables to be set up,
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// so it's safe to call this really early on. This function also lets you distinguish
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// between the inability to find the given type and its value just happening to be 0.
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unsigned long getauxval(unsigned long type, bool* found_match = NULL) {
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for (Elf32_auxv_t* v = auxv; v->a_type != AT_NULL; ++v) {
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if (v->a_type == type) {
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if (found_match != NULL) {
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*found_match = true;
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}
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return v->a_un.a_val;
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}
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}
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if (found_match != NULL) {
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*found_match = false;
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}
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return 0;
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}
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int argc;
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char** argv;
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char** envp;
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Elf32_auxv_t* auxv;
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private:
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// Disallow copy and assignment.
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KernelArgumentBlock(const KernelArgumentBlock&);
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void operator=(const KernelArgumentBlock&);
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};
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#endif // KERNEL_ARGUMENT_BLOCK_H
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