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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-exception6//7//===----------------------------------------------------------------------===//8//9// Handle the __tls_get_addr call.10//11// All this magic is specific to glibc and is required to workaround12// the lack of interface that would tell us about the Dynamic TLS (DTLS).13// https://sourceware.org/bugzilla/show_bug.cgi?id=1629114//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-opt19// the malloc interceptor to keep track of the last allocation, similar20// to how we handle __libc_memalign; however, this adds some overhead21// (since malloc, unlike __libc_memalign, is commonly called), and22// requires care to avoid false negatives for LeakSanitizer.23// Instead, we rely on our internal allocators - which keep track of all24// its allocations - to determine if an address points to a malloc25// allocation.26//27// There exists a since-deprecated version of Google's internal glibc fork28// that used __signal_safe_memalign. DTLS_on_tls_get_addr relied on a29// heuristic check (is the allocation 16 bytes from the start of a page30// boundary?), which was sometimes erroneous:31// https://bugs.chromium.org/p/chromium/issues/detail?id=1275223#c1532// Since that check has no practical use anymore, we have removed it.33//34//===----------------------------------------------------------------------===//35 36#ifndef SANITIZER_TLS_GET_ADDR_H37#define SANITIZER_TLS_GET_ADDR_H38 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(&dtls->dtv_block, 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(&block->next, 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 __sanitizer82 83#endif // SANITIZER_TLS_GET_ADDR_H84