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 // The matters get worse because the glibc implementation changed between
16 // 2.18 and 2.19:
17 // https://groups.google.com/forum/#!topic/address-sanitizer/BfwYD8HMxTM
18 //
19 // Before 2.19, every DTLS chunk is allocated with __libc_memalign,
20 // which we intercept and thus know where is the DTLS.
21 // Since 2.19, DTLS chunks are allocated with __signal_safe_memalign,
22 // which is an internal function that wraps a mmap call, neither of which
23 // we can intercept. Luckily, __signal_safe_memalign has a simple parseable
24 // header which we can use.
25 //
26 //===----------------------------------------------------------------------===//
27 
28 #ifndef SANITIZER_TLS_GET_ADDR_H
29 #define SANITIZER_TLS_GET_ADDR_H
30 
31 #include "sanitizer_atomic.h"
32 #include "sanitizer_common.h"
33 
34 namespace __sanitizer {
35 
36 struct DTLS {
37   // Array of DTLS chunks for the current Thread.
38   // If beg == 0, the chunk is unused.
39   struct DTV {
40     uptr beg, size;
41   };
42   struct DTVBlock {
43     atomic_uintptr_t next;
44     DTV dtvs[(4096UL - sizeof(next)) / sizeof(DTLS::DTV)];
45   };
46 
47   static_assert(sizeof(DTVBlock) <= 4096UL, "Unexpected block size");
48 
49   atomic_uintptr_t dtv_block;
50 
51   // Auxiliary fields, don't access them outside sanitizer_tls_get_addr.cpp
52   uptr last_memalign_size;
53   uptr last_memalign_ptr;
54 };
55 
56 template <typename Fn>
57 void ForEachDVT(DTLS *dtls, const Fn &fn) {
58   DTLS::DTVBlock *block =
59       (DTLS::DTVBlock *)atomic_load(&dtls->dtv_block, memory_order_acquire);
60   while (block) {
61     int id = 0;
62     for (auto &d : block->dtvs) fn(d, id++);
63     block = (DTLS::DTVBlock *)atomic_load(&block->next, memory_order_acquire);
64   }
65 }
66 
67 // Returns pointer and size of a linker-allocated TLS block.
68 // Each block is returned exactly once.
69 DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res, uptr static_tls_begin,
70                                 uptr static_tls_end);
71 void DTLS_on_libc_memalign(void *ptr, uptr size);
72 DTLS *DTLS_Get();
73 void DTLS_Destroy();  // Make sure to call this before the thread is destroyed.
74 // Returns true if DTLS of suspended thread is in destruction process.
75 bool DTLSInDestruction(DTLS *dtls);
76 
77 }  // namespace __sanitizer
78 
79 #endif  // SANITIZER_TLS_GET_ADDR_H
80