libc/startup/linux/riscv/tls.cpp

   1 //===-- Implementation of tls for riscv -----------------------------------===//
   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/threads/thread.h"
  11 #include "src/string/memory_utils/inline_memcpy.h"
  12 #include "startup/linux/do_start.h"
  13
  14 #include <sys/mman.h>
  15 #include <sys/syscall.h>
  16
  17 namespace LIBC_NAMESPACE {
  18
  19 #ifdef SYS_mmap2
  20 static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap2;
  21 #elif SYS_mmap
  22 static constexpr long MMAP_SYSCALL_NUMBER = SYS_mmap;
  23 #else
  24 #error "mmap and mmap2 syscalls not available."
  25 #endif
  26
  27 void init_tls(TLSDescriptor &tls_descriptor) {
  28   if (app.tls.size == 0) {
  29     tls_descriptor.size = 0;
  30     tls_descriptor.tp = 0;
  31     return;
  32   }
  33
  34   // riscv64 follows the variant 1 TLS layout:
  35   const uintptr_t size_of_pointers = 2 * sizeof(uintptr_t);
  36   uintptr_t padding = 0;
  37   const uintptr_t ALIGNMENT_MASK = app.tls.align - 1;
  38   uintptr_t diff = size_of_pointers & ALIGNMENT_MASK;
  39   if (diff != 0)
  40     padding += (ALIGNMENT_MASK - diff) + 1;
  41
  42   uintptr_t alloc_size = size_of_pointers + padding + app.tls.size;
  43
  44   // We cannot call the mmap function here as the functions set errno on
  45   // failure. Since errno is implemented via a thread local variable, we cannot
  46   // use errno before TLS is setup.
  47   long mmap_ret_val = syscall_impl<long>(MMAP_SYSCALL_NUMBER, nullptr,
  48                                          alloc_size, PROT_READ | PROT_WRITE,
  49                                          MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
  50   // We cannot check the return value with MAP_FAILED as that is the return
  51   // of the mmap function and not the mmap syscall.
  52   if (mmap_ret_val < 0 && static_cast<uintptr_t>(mmap_ret_val) > -app.page_size)
  53     syscall_impl<long>(SYS_exit, 1);
  54   uintptr_t thread_ptr = uintptr_t(reinterpret_cast<uintptr_t *>(mmap_ret_val));
  55   uintptr_t tls_addr = thread_ptr + size_of_pointers + padding;
  56   inline_memcpy(reinterpret_cast<char *>(tls_addr),
  57                 reinterpret_cast<const char *>(app.tls.address),
  58                 app.tls.init_size);
  59   tls_descriptor.size = alloc_size;
  60   tls_descriptor.addr = thread_ptr;
  61   tls_descriptor.tp = tls_addr;
  62 }
  63
  64 void cleanup_tls(uintptr_t addr, uintptr_t size) {
  65   if (size == 0)
  66     return;
  67   syscall_impl<long>(SYS_munmap, addr, size);
  68 }
  69
  70 bool set_thread_ptr(uintptr_t val) {
  71   LIBC_INLINE_ASM("mv tp, %0\n\t" : : "r"(val));
  72   return true;
  73 }
  74 } // namespace LIBC_NAMESPACE