libc/startup/linux/aarch64/tls.cpp

   1 //===-- Implementation of tls for aarch64 ---------------------------------===//
   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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/__support/OSUtil/syscall.h"
  10 #include "src/__support/macros/config.h"
  11 #include "src/__support/threads/thread.h"
  12 #include "src/string/memory_utils/inline_memcpy.h"
  13 #include "startup/linux/do_start.h"
  14
  15 #include <arm_acle.h>
  16 #include <sys/mman.h>
  17 #include <sys/syscall.h>
  18
  19 // Source documentation:
  20 // https://github.com/ARM-software/abi-aa/tree/main/sysvabi64
  21
  22 namespace LIBC_NAMESPACE_DECL {
  23
  24 #ifdef SYS_mmap2
  25 static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap2;
  26 #elif SYS_mmap
  27 static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap;
  28 #else
  29 #error "mmap and mmap2 syscalls not available."
  30 #endif
  31
  32 void init_tls(TLSDescriptor &tls_descriptor) {
  33   if (app.tls.size == 0) {
  34     tls_descriptor.size = 0;
  35     tls_descriptor.tp = 0;
  36     return;
  37   }
  38
  39   // aarch64 follows the variant 1 TLS layout:
  40   //
  41   // 1. First entry is the dynamic thread vector pointer
  42   // 2. Second entry is a 8-byte reserved word.
  43   // 3. Padding for alignment.
  44   // 4. The TLS data from the ELF image.
  45   //
  46   // The thread pointer points to the first entry.
  47
  48   const uintptr_t size_of_pointers = 2 * sizeof(uintptr_t);
  49   uintptr_t padding = 0;
  50   const uintptr_t ALIGNMENT_MASK = app.tls.align - 1;
  51   uintptr_t diff = size_of_pointers & ALIGNMENT_MASK;
  52   if (diff != 0)
  53     padding += (ALIGNMENT_MASK - diff) + 1;
  54
  55   uintptr_t alloc_size = size_of_pointers + padding + app.tls.size;
  56
  57   // We cannot call the mmap function here as the functions set errno on
  58   // failure. Since errno is implemented via a thread local variable, we cannot
  59   // use errno before TLS is setup.
  60   long mmap_ret_val = syscall_impl<long>(MMAP_SYSCALL_NUMBER, nullptr,
  61                                          alloc_size, PROT_READ | PROT_WRITE,
  62                                          MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
  63   // We cannot check the return value with MAP_FAILED as that is the return
  64   // of the mmap function and not the mmap syscall.
  65   if (mmap_ret_val < 0 && static_cast<uintptr_t>(mmap_ret_val) > -app.page_size)
  66     syscall_impl<long>(SYS_exit, 1);
  67   uintptr_t thread_ptr = uintptr_t(reinterpret_cast<uintptr_t *>(mmap_ret_val));
  68   uintptr_t tls_addr = thread_ptr + size_of_pointers + padding;
  69   inline_memcpy(reinterpret_cast<char *>(tls_addr),
  70                 reinterpret_cast<const char *>(app.tls.address),
  71                 app.tls.init_size);
  72   tls_descriptor.size = alloc_size;
  73   tls_descriptor.addr = thread_ptr;
  74   tls_descriptor.tp = thread_ptr;
  75 }
  76
  77 void cleanup_tls(uintptr_t addr, uintptr_t size) {
  78   if (size == 0)
  79     return;
  80   syscall_impl<long>(SYS_munmap, addr, size);
  81 }
  82
  83 bool set_thread_ptr(uintptr_t val) {
  84 // The PR for __arm_wsr64 support in GCC was merged on Dec 6, 2023, and it is
  85 // not yet usable in 13.3.0
  86 // https://github.com/gcc-mirror/gcc/commit/fc42900d21abd5eacb7537c3c8ffc5278d510195
  87 #if __has_builtin(__builtin_arm_wsr64)
  88   __builtin_arm_wsr64("tpidr_el0", val);
  89 #elif __has_builtin(__builtin_aarch64_wsr)
  90   __builtin_aarch64_wsr("tpidr_el0", val);
  91 #elif defined(__GNUC__)
  92   asm volatile("msr tpidr_el0, %0" ::"r"(val));
  93 #else
  94 #error "Unsupported compiler"
  95 #endif
  96   return true;
  97 }
  98 } // namespace LIBC_NAMESPACE_DECL