llvm-project

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//===-- sanitizer_tls_get_addr.cpp ----------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Handle the __tls_get_addr call.
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//
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//===----------------------------------------------------------------------===//
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#include "sanitizer_tls_get_addr.h"
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#include "sanitizer_allocator_interface.h"
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#include "sanitizer_atomic.h"
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#include "sanitizer_flags.h"
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#include "sanitizer_platform_interceptors.h"
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namespace __sanitizer {
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#if SANITIZER_INTERCEPT_TLS_GET_ADDR
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// The actual parameter that comes to __tls_get_addr
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// is a pointer to a struct with two words in it:
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struct TlsGetAddrParam {
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  uptr dso_id;
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  uptr offset;
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};
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// This must be static TLS
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__attribute__((tls_model("initial-exec")))
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static __thread DTLS dtls;
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// Make sure we properly destroy the DTLS objects:
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// this counter should never get too large.
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static atomic_uintptr_t number_of_live_dtls;
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static const uptr kDestroyedThread = -1;
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static void DTLS_Deallocate(DTLS::DTVBlock *block) {
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  VReport(2, "__tls_get_addr: DTLS_Deallocate %p\n", (void *)block);
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  UnmapOrDie(block, sizeof(DTLS::DTVBlock));
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  atomic_fetch_sub(&number_of_live_dtls, 1, memory_order_relaxed);
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}
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static DTLS::DTVBlock *DTLS_NextBlock(atomic_uintptr_t *cur) {
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  uptr v = atomic_load(cur, memory_order_acquire);
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  if (v == kDestroyedThread)
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    return nullptr;
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  DTLS::DTVBlock *next = (DTLS::DTVBlock *)v;
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  if (next)
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    return next;
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  DTLS::DTVBlock *new_dtv =
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      (DTLS::DTVBlock *)MmapOrDie(sizeof(DTLS::DTVBlock), "DTLS_NextBlock");
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  uptr prev = 0;
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  if (!atomic_compare_exchange_strong(cur, &prev, (uptr)new_dtv,
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                                      memory_order_seq_cst)) {
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    UnmapOrDie(new_dtv, sizeof(DTLS::DTVBlock));
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    return (DTLS::DTVBlock *)prev;
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  }
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  uptr num_live_dtls =
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      atomic_fetch_add(&number_of_live_dtls, 1, memory_order_relaxed);
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  VReport(2, "__tls_get_addr: DTLS_NextBlock %p %zd\n", (void *)&dtls,
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          num_live_dtls);
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  return new_dtv;
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}
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static DTLS::DTV *DTLS_Find(uptr id) {
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  VReport(2, "__tls_get_addr: DTLS_Find %p %zd\n", (void *)&dtls, id);
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  static constexpr uptr kPerBlock = ARRAY_SIZE(DTLS::DTVBlock::dtvs);
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  DTLS::DTVBlock *cur = DTLS_NextBlock(&dtls.dtv_block);
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  if (!cur)
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    return nullptr;
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  for (; id >= kPerBlock; id -= kPerBlock) cur = DTLS_NextBlock(&cur->next);
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  return cur->dtvs + id;
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}
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void DTLS_Destroy() {
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  if (!common_flags()->intercept_tls_get_addr) return;
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  VReport(2, "__tls_get_addr: DTLS_Destroy %p\n", (void *)&dtls);
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  DTLS::DTVBlock *block = (DTLS::DTVBlock *)atomic_exchange(
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      &dtls.dtv_block, kDestroyedThread, memory_order_release);
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  while (block) {
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    DTLS::DTVBlock *next =
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        (DTLS::DTVBlock *)atomic_load(&block->next, memory_order_acquire);
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    DTLS_Deallocate(block);
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    block = next;
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  }
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}
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#if defined(__powerpc64__) || defined(__mips__)
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// This is glibc's TLS_DTV_OFFSET:
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// "Dynamic thread vector pointers point 0x8000 past the start of each
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//  TLS block." (sysdeps/<arch>/dl-tls.h)
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static const uptr kDtvOffset = 0x8000;
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#elif defined(__riscv)
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// This is glibc's TLS_DTV_OFFSET:
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// "Dynamic thread vector pointers point 0x800 past the start of each
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// TLS block." (sysdeps/riscv/dl-tls.h)
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static const uptr kDtvOffset = 0x800;
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#else
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static const uptr kDtvOffset = 0;
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#endif
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extern "C" {
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SANITIZER_WEAK_ATTRIBUTE
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uptr __sanitizer_get_allocated_size(const void *p);
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SANITIZER_WEAK_ATTRIBUTE
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const void *__sanitizer_get_allocated_begin(const void *p);
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}
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DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
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                                uptr static_tls_begin, uptr static_tls_end) {
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  if (!common_flags()->intercept_tls_get_addr) return 0;
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  TlsGetAddrParam *arg = reinterpret_cast<TlsGetAddrParam *>(arg_void);
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  uptr dso_id = arg->dso_id;
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  DTLS::DTV *dtv = DTLS_Find(dso_id);
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  if (!dtv || dtv->beg)
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    return 0;
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  uptr tls_size = 0;
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  uptr tls_beg = reinterpret_cast<uptr>(res) - arg->offset - kDtvOffset;
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  VReport(2,
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          "__tls_get_addr: %p {0x%zx,0x%zx} => %p; tls_beg: 0x%zx; sp: %p "
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          "num_live_dtls %zd\n",
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          (void *)arg, arg->dso_id, arg->offset, res, tls_beg, (void *)&tls_beg,
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          atomic_load(&number_of_live_dtls, memory_order_relaxed));
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  if (dtls.last_memalign_ptr == tls_beg) {
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    tls_size = dtls.last_memalign_size;
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    VReport(2, "__tls_get_addr: glibc <=2.24 suspected; tls={0x%zx,0x%zx}\n",
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            tls_beg, tls_size);
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  } else if (tls_beg >= static_tls_begin && tls_beg < static_tls_end) {
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    // This is the static TLS block which was initialized / unpoisoned at thread
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    // creation.
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    VReport(2, "__tls_get_addr: static tls: 0x%zx\n", tls_beg);
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    tls_size = 0;
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  } else if (const void *start =
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                 __sanitizer_get_allocated_begin((void *)tls_beg)) {
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    tls_beg = (uptr)start;
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    tls_size = __sanitizer_get_allocated_size(start);
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    VReport(2, "__tls_get_addr: glibc >=2.25 suspected; tls={0x%zx,0x%zx}\n",
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            tls_beg, tls_size);
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  } else {
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    VReport(2, "__tls_get_addr: Can't guess glibc version\n");
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    // This may happen inside the DTOR of main thread, so just ignore it.
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    tls_size = 0;
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  }
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  dtv->beg = tls_beg;
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  dtv->size = tls_size;
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  return dtv;
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}
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void DTLS_on_libc_memalign(void *ptr, uptr size) {
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  if (!common_flags()->intercept_tls_get_addr) return;
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  VReport(2, "DTLS_on_libc_memalign: %p 0x%zx\n", ptr, size);
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  dtls.last_memalign_ptr = reinterpret_cast<uptr>(ptr);
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  dtls.last_memalign_size = size;
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}
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DTLS *DTLS_Get() { return &dtls; }
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bool DTLSInDestruction(DTLS *dtls) {
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  return atomic_load(&dtls->dtv_block, memory_order_relaxed) ==
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         kDestroyedThread;
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}
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#else
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void DTLS_on_libc_memalign(void *ptr, uptr size) {}
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DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res,
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  unsigned long, unsigned long) { return 0; }
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DTLS *DTLS_Get() { return 0; }
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void DTLS_Destroy() {}
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bool DTLSInDestruction(DTLS *dtls) {
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  UNREACHABLE("dtls is unsupported on this platform!");
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}
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#endif  // SANITIZER_INTERCEPT_TLS_GET_ADDR
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}  // namespace __sanitizer
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