84 lines
2.5 KiB
C++
84 lines
2.5 KiB
C++
//===-- Implementation of crt for aarch64 ---------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "config/linux/app.h"
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#include "src/__support/OSUtil/syscall.h"
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#include <linux/auxvec.h>
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#include <linux/elf.h>
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#include <stdint.h>
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#include <sys/syscall.h>
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extern "C" int main(int, char **, char **);
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// Source documentation:
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// https://github.com/ARM-software/abi-aa/tree/main/sysvabi64
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namespace __llvm_libc {
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AppProperties app;
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} // namespace __llvm_libc
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using __llvm_libc::app;
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struct Args {
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// In the ARM64 ABI, arguments are usually passed in registers. x0 is a
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// doubleword register, so this is 64 bit.
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uint64_t argc;
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// C++ Doesn't have flexible arrays: P1039 proposes to fix this, but for now
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// we just fake it. Even if argc is zero, "argv[argc] shall be a null
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// pointer" (ISO C 5.1.2.2.1) so one is fine.
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uint64_t argv[1];
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};
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// TODO: Would be nice to use the aux entry structure from elf.h when available.
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struct AuxEntry {
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uint64_t type;
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uint64_t value;
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};
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extern "C" void _start() {
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uintptr_t *frame_ptr =
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reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
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// Skip the Frame Pointer and the Link Register
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// https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
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// Section 6.2.3
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Args *args = reinterpret_cast<Args *>(frame_ptr + 2);
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// After the argv array, is a 8-byte long NULL value before the array of env
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// values. The end of the env values is marked by another 8-byte long NULL
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// value. We step over it (the "+ 1" below) to get to the env values.
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uint64_t *env_ptr = args->argv + args->argc + 1;
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uint64_t *env_end_marker = env_ptr;
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while (*env_end_marker)
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++env_end_marker;
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// After the env array, is the aux-vector. The end of the aux-vector is
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// denoted by an AT_NULL entry.
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for (AuxEntry *aux_entry = reinterpret_cast<AuxEntry *>(env_end_marker + 1);
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aux_entry->type != AT_NULL; ++aux_entry) {
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switch (aux_entry->type) {
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case AT_PAGESZ:
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app.pageSize = aux_entry->value;
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break;
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default:
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break; // TODO: Read other useful entries from the aux vector.
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}
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}
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// TODO: Init TLS
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__llvm_libc::syscall(SYS_exit,
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main(args->argc, reinterpret_cast<char **>(args->argv),
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reinterpret_cast<char **>(env_ptr)));
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}
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