libsanitizer/sanitizer_common/sanitizer_tls_get_addr.h

   1 //===-- sanitizer_tls_get_addr.h --------------------------------*- C++ -*-===//
   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 // Handle the __tls_get_addr call.
  10 //
  11 // All this magic is specific to glibc and is required to workaround
  12 // the lack of interface that would tell us about the Dynamic TLS (DTLS).
  13 // https://sourceware.org/bugzilla/show_bug.cgi?id=16291
  14 //
  15 // Before 2.25: every DTLS chunk is allocated with __libc_memalign,
  16 // which we intercept and thus know where is the DTLS.
  17 //
  18 // Since 2.25: DTLS chunks are allocated with malloc. We could co-opt
  19 // the malloc interceptor to keep track of the last allocation, similar
  20 // to how we handle __libc_memalign; however, this adds some overhead
  21 // (since malloc, unlike __libc_memalign, is commonly called), and
  22 // requires care to avoid false negatives for LeakSanitizer.
  23 // Instead, we rely on our internal allocators - which keep track of all
  24 // its allocations - to determine if an address points to a malloc
  25 // allocation.
  26 //
  27 // There exists a since-deprecated version of Google's internal glibc fork
  28 // that used __signal_safe_memalign. DTLS_on_tls_get_addr relied on a
  29 // heuristic check (is the allocation 16 bytes from the start of a page
  30 // boundary?), which was sometimes erroneous:
  31 //     https://bugs.chromium.org/p/chromium/issues/detail?id=1275223#c15
  32 // Since that check has no practical use anymore, we have removed it.
  33 //
  34 //===----------------------------------------------------------------------===//
  35
  36 #ifndef SANITIZER_TLS_GET_ADDR_H
  37 #define SANITIZER_TLS_GET_ADDR_H
  38
  39 #include "sanitizer_atomic.h"
  40 #include "sanitizer_common.h"
  41
  42 namespace __sanitizer {
  43
  44 struct DTLS {
  45   // Array of DTLS chunks for the current Thread.
  46   // If beg == 0, the chunk is unused.
  47   struct DTV {
  48     uptr beg, size;
  49   };
  50   struct DTVBlock {
  51     atomic_uintptr_t next;
  52     DTV dtvs[(4096UL - sizeof(next)) / sizeof(DTLS::DTV)];
  53   };
  54
  55   static_assert(sizeof(DTVBlock) <= 4096UL, "Unexpected block size");
  56
  57   atomic_uintptr_t dtv_block;
  58
  59   // Auxiliary fields, don't access them outside sanitizer_tls_get_addr.cpp
  60   uptr last_memalign_size;
  61   uptr last_memalign_ptr;
  62 };
  63
  64 template <typename Fn>
  65 void ForEachDVT(DTLS *dtls, const Fn &fn) {
  66   DTLS::DTVBlock *block =
  67       (DTLS::DTVBlock *)atomic_load(&dtls->dtv_block, memory_order_acquire);
  68   while (block) {
  69     int id = 0;
  70     for (auto &d : block->dtvs) fn(d, id++);
  71     block = (DTLS::DTVBlock *)atomic_load(&block->next, memory_order_acquire);
  72   }
  73 }
  74
  75 // Returns pointer and size of a linker-allocated TLS block.
  76 // Each block is returned exactly once.
  77 DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res, uptr static_tls_begin,
  78                                 uptr static_tls_end);
  79 void DTLS_on_libc_memalign(void *ptr, uptr size);
  80 DTLS *DTLS_Get();
  81 void DTLS_Destroy();  // Make sure to call this before the thread is destroyed.
  82 // Returns true if DTLS of suspended thread is in destruction process.
  83 bool DTLSInDestruction(DTLS *dtls);
  84
  85 }  // namespace __sanitizer
  86
  87 #endif  // SANITIZER_TLS_GET_ADDR_H