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>
ForEachDVT(DTLS * dtls,const Fn & 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
88