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/*
* Copyright (C) 2017 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "private/KernelArgumentBlock.h"
// The offset from the linker's original program header load addresses to
// the load addresses when embedded into a binary. Set by the extract_linker
// tool.
extern const char __dlwrap_linker_offset;
// The real entry point of the binary to use after linker bootstrapping.
__LIBC_HIDDEN__ extern "C" void _start();
/* Find the load bias and base address of an executable or shared object loaded
* by the kernel. The ELF file's PHDR table must have a PT_PHDR entry.
*
* A VDSO doesn't have a PT_PHDR entry in its PHDR table.
*/
static void get_elf_base_from_phdr(const ElfW(Phdr)* phdr_table, size_t phdr_count,
ElfW(Addr)* base, ElfW(Addr)* load_bias) {
for (size_t i = 0; i < phdr_count; ++i) {
if (phdr_table[i].p_type == PT_PHDR) {
*load_bias = reinterpret_cast<ElfW(Addr)>(phdr_table) - phdr_table[i].p_vaddr;
*base = reinterpret_cast<ElfW(Addr)>(phdr_table) - phdr_table[i].p_offset;
return;
}
}
}
/*
* This is the entry point for the linker wrapper, which finds
* the real linker, then bootstraps into it.
*/
extern "C" ElfW(Addr) __linker_init(void* raw_args) {
KernelArgumentBlock args(raw_args);
ElfW(Addr) base_addr = 0;
ElfW(Addr) load_bias = 0;
get_elf_base_from_phdr(
reinterpret_cast<ElfW(Phdr)*>(args.getauxval(AT_PHDR)), args.getauxval(AT_PHNUM),
&base_addr, &load_bias);
ElfW(Addr) linker_addr = base_addr + reinterpret_cast<uintptr_t>(&__dlwrap_linker_offset);
ElfW(Addr) linker_entry_offset = reinterpret_cast<ElfW(Ehdr)*>(linker_addr)->e_entry;
for (ElfW(auxv_t)* v = args.auxv; v->a_type != AT_NULL; ++v) {
if (v->a_type == AT_BASE) {
// Set AT_BASE to the embedded linker
v->a_un.a_val = linker_addr;
}
if (v->a_type == AT_ENTRY) {
// Set AT_ENTRY to the proper entry point
v->a_un.a_val = reinterpret_cast<ElfW(Addr)>(&_start);
}
}
// Return address of linker entry point
return linker_addr + linker_entry_offset;
}
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