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 // Auxiliary fields, don't access them outside sanitizer_tls_get_addr.cpp 60 uptr last_memalign_size; 61 uptr last_memalign_ptr; 62}; 63 64template <typename Fn> 65void 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. 77DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res, uptr static_tls_begin, 78 uptr static_tls_end); 79void DTLS_on_libc_memalign(void *ptr, uptr size); 80DTLS *DTLS_Get(); 81void DTLS_Destroy(); // Make sure to call this before the thread is destroyed. 82// Returns true if DTLS of suspended thread is in destruction process. 83bool DTLSInDestruction(DTLS *dtls); 84 85} // namespace __sanitizer 86 87#endif // SANITIZER_TLS_GET_ADDR_H 88