| // Copyright 2016 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #pragma once |
| |
| #include <stdint.h> |
| |
| // Given the base and size of the stack block, compute the appropriate |
| // initial SP value for an initial thread according to the C calling |
| // convention for the machine. |
| static inline uintptr_t compute_initial_stack_pointer(uintptr_t base, |
| size_t size) { |
| // Assume stack grows down. |
| uintptr_t sp = base + size; |
| |
| // The x86-64 and AArch64 ABIs require 16-byte alignment. |
| // The 32-bit ARM ABI only requires 8-byte alignment, but |
| // 16-byte alignment is preferable for NEON so use it there too. |
| sp &= -16; |
| |
| #ifdef __x86_64__ |
| // The x86-64 ABI requires %rsp % 16 = 8 on entry. The zero word |
| // at (%rsp) serves as the return address for the outermost frame. |
| sp -= 8; |
| #elif defined(__arm__) || defined(__aarch64__) |
| // The ARMv7 and ARMv8 ABIs both just require that SP be aligned. |
| #else |
| # error what machine? |
| #endif |
| |
| return sp; |
| } |
