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
42namespace __sanitizer {
43
44struct 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
60template <typename Fn>
61void ForEachDVT(DTLS *dtls, const Fn &fn) {
62 DTLS::DTVBlock *block =
63 (DTLS::DTVBlock *)atomic_load(a: &dtls->dtv_block, mo: memory_order_acquire);
64 while (block) {
65 int id = 0;
66 for (auto &d : block->dtvs) fn(d, id++);
67 block = (DTLS::DTVBlock *)atomic_load(a: &block->next, mo: memory_order_acquire);
68 }
69}
70
71// Returns pointer and size of a linker-allocated TLS block.
72// Each block is returned exactly once.
73DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res, uptr static_tls_begin,
74 uptr static_tls_end);
75void DTLS_on_libc_memalign(void *ptr, uptr size);
76DTLS *DTLS_Get();
77void DTLS_Destroy(); // Make sure to call this before the thread is destroyed.
78// Returns true if DTLS of suspended thread is in destruction process.
79bool DTLSInDestruction(DTLS *dtls);
80
81} // namespace __sanitizer
82
83#endif // SANITIZER_TLS_GET_ADDR_H
84