2bc994456c
* separate initialization routines into _start and do_start for all architectures. * lift do_start as a separate object library to avoid code duplication. * (addtionally) address the problem of building hermetic libc with -fstack-pointer-* The `crt1.o` is now a merged result of three components: ``` ___ |___ x86_64 | |_______ start.cpp.o <- _start (loads process initial stack and aligns stack pointer) | |_______ tls.cpp.o <- init_tls, cleanup_tls, set_thread_pointer (TLS related routines) |___ do_start.cpp.o <- do_start (sets up global variables and invokes the main function) ```
25 lines
1.3 KiB
C++
25 lines
1.3 KiB
C++
//===-- Implementation of _start 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 "startup/linux/do_start.h"
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extern "C" [[noreturn]] void _start() {
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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. Note that this only works if the current function
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// is not using any callee-saved registers (x19 to x28). If the
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// function uses such registers, then their value is pushed on to the
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// stack before the frame pointer an link register values. That breaks
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// the assumption that stepping over the frame pointer and link register
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// will take us to the previous stack pointer. That is the reason why the
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// actual business logic of the startup code is pushed into a non-inline
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// function do_start so that this function is free of any stack usage.
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LIBC_NAMESPACE::app.args = reinterpret_cast<LIBC_NAMESPACE::Args *>(
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reinterpret_cast<uintptr_t *>(__builtin_frame_address(0)) + 2);
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LIBC_NAMESPACE::do_start();
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}
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