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 88