95 lines · cpp
1//===-- Implementation of tls for x86_64 ----------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "src/__support/OSUtil/syscall.h"10#include "src/__support/macros/config.h"11#include "src/string/memory_utils/inline_memcpy.h"12#include "startup/linux/do_start.h"13 14#include <asm/prctl.h>15#include <sys/mman.h>16#include <sys/syscall.h>17 18namespace LIBC_NAMESPACE_DECL {19 20#ifdef SYS_mmap221static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap2;22#elif SYS_mmap23static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap;24#else25#error "mmap and mmap2 syscalls not available."26#endif27 28// TODO: Also generalize this routine and handle dynamic loading properly.29void init_tls(TLSDescriptor &tls_descriptor) {30 if (app.tls.size == 0) {31 tls_descriptor.size = 0;32 tls_descriptor.tp = 0;33 return;34 }35 36 // We will assume the alignment is always a power of two.37 uintptr_t tls_size = app.tls.size & -app.tls.align;38 if (tls_size != app.tls.size)39 tls_size += app.tls.align;40 41 // Per the x86_64 TLS ABI, the entry pointed to by the thread pointer is the42 // address of the TLS block. So, we add more size to accomodate this address43 // entry.44 // We also need to include space for the stack canary. The canary is at45 // offset 0x28 (40) and is of size uintptr_t.46 uintptr_t tls_size_with_addr = tls_size + sizeof(uintptr_t) + 40;47 48 // We cannot call the mmap function here as the functions set errno on49 // failure. Since errno is implemented via a thread local variable, we cannot50 // use errno before TLS is setup.51 long mmap_retval = syscall_impl<long>(52 MMAP_SYSCALL_NUMBER, nullptr, tls_size_with_addr, PROT_READ | PROT_WRITE,53 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);54 // We cannot check the return value with MAP_FAILED as that is the return55 // of the mmap function and not the mmap syscall.56 if (!linux_utils::is_valid_mmap(mmap_retval))57 syscall_impl<long>(SYS_exit, 1);58 uintptr_t *tls_addr = reinterpret_cast<uintptr_t *>(mmap_retval);59 60 // x86_64 TLS faces down from the thread pointer with the first entry61 // pointing to the address of the first real TLS byte.62 uintptr_t end_ptr = reinterpret_cast<uintptr_t>(tls_addr) + tls_size;63 *reinterpret_cast<uintptr_t *>(end_ptr) = end_ptr;64 65 inline_memcpy(reinterpret_cast<char *>(tls_addr),66 reinterpret_cast<const char *>(app.tls.address),67 app.tls.init_size);68 uintptr_t *stack_guard_addr = reinterpret_cast<uintptr_t *>(end_ptr + 40);69 // Setting the stack guard to a random value.70 // We cannot call the get_random function here as the function sets errno on71 // failure. Since errno is implemented via a thread local variable, we cannot72 // use errno before TLS is setup.73 long stack_guard_retval =74 syscall_impl(SYS_getrandom, reinterpret_cast<long>(stack_guard_addr),75 sizeof(uint64_t), 0);76 if (stack_guard_retval < 0)77 syscall_impl(SYS_exit, 1);78 79 tls_descriptor = {tls_size_with_addr, reinterpret_cast<uintptr_t>(tls_addr),80 end_ptr};81 return;82}83 84void cleanup_tls(uintptr_t addr, uintptr_t size) {85 if (size == 0)86 return;87 syscall_impl<long>(SYS_munmap, addr, size);88}89 90// Sets the thread pointer to |val|. Returns true on success, false on failure.91bool set_thread_ptr(uintptr_t val) {92 return syscall_impl(SYS_arch_prctl, ARCH_SET_FS, val) != -1;93}94} // namespace LIBC_NAMESPACE_DECL95