pdns/mtasker_ucontext.cc

   1 /*
   2  * This file is part of PowerDNS or dnsdist.
   3  * Copyright -- PowerDNS.COM B.V. and its contributors
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of version 2 of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * In addition, for the avoidance of any doubt, permission is granted to
  10  * link this program with OpenSSL and to (re)distribute the binaries
  11  * produced as the result of such linking.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21  */
  22 #include "mtasker_context.hh"
  23 #include <system_error>
  24 #include <exception>
  25 #include <cstring>
  26 #include <cassert>
  27 #include <signal.h>
  28 #include <ucontext.h>
  29
  30 #ifdef PDNS_USE_VALGRIND
  31 #include <valgrind/valgrind.h>
  32 #endif /* PDNS_USE_VALGRIND */
  33
  34 #ifdef HAVE_FIBER_SANITIZER
  35 __thread void* t_mainStack{nullptr};
  36 __thread size_t t_mainStackSize{0};
  37 #endif /* HAVE_FIBER_SANITIZER */
  38
  39 template <typename Message> static __attribute__((noinline, cold, noreturn))
  40 void
  41 throw_errno (Message&& msg) {
  42     throw std::system_error
  43             (errno, std::system_category(), std::forward<Message>(msg));
  44 }
  45
  46 static inline
  47 std::pair<int, int>
  48 splitPointer (void* const ptr) noexcept {
  49     static_assert (sizeof(int) == 4, "splitPointer() requires an 4 byte 'int'");
  50 // In theory, we need this assertion. In practice, it prevents compilation
  51 // on EL6 i386. Without the assertion, everything works.
  52 // If you ever run into trouble with this code, please heed the warnings at
  53 // http://man7.org/linux/man-pages/man3/makecontext.3.html#NOTES
  54 //    static_assert (sizeof(uintptr_t) == 8,
  55 //                    "splitPointer() requires an 8 byte 'uintptr_t'");
  56     std::pair<int, int> words;
  57     auto rep = reinterpret_cast<uintptr_t>(ptr);
  58     uint32_t const hw = rep >> 32;
  59     auto const lw = static_cast<uint32_t>(rep);
  60     std::memcpy (&words.first, &hw, 4);
  61     std::memcpy (&words.second, &lw, 4);
  62     return words;
  63 }
  64
  65 template <typename T> static inline
  66 T*
  67 joinPtr (int const first, int const second) noexcept {
  68     static_assert (sizeof(int) == 4, "joinPtr() requires an 4 byte 'int'");
  69 // See above.
  70 //    static_assert (sizeof(uintptr_t) == 8,
  71 //                    "joinPtr() requires an 8 byte 'uintptr_t'");
  72     uint32_t hw;
  73     uint32_t lw;
  74     std::memcpy (&hw, &first, 4);
  75     std::memcpy (&lw, &second, 4);
  76     return reinterpret_cast<T*>((static_cast<uintptr_t>(hw) << 32) | lw);
  77 }
  78
  79 extern "C" {
  80 static
  81 void
  82 threadWrapper (int const ctx0, int const ctx1, int const fun0, int const fun1) {
  83     notifyStackSwitchDone();
  84     auto ctx = joinPtr<pdns_ucontext_t>(ctx0, ctx1);
  85     try {
  86         auto start = std::move(*joinPtr<boost::function<void()>>(fun0, fun1));
  87         start();
  88     } catch (...) {
  89         ctx->exception = std::current_exception();
  90     }
  91     notifyStackSwitchToKernel();
  92 }
  93 } // extern "C"
  94
  95 pdns_ucontext_t::pdns_ucontext_t() {
  96     uc_mcontext = new ::ucontext_t();
  97     uc_link = nullptr;
  98 #ifdef PDNS_USE_VALGRIND
  99     valgrind_id = 0;
 100 #endif /* PDNS_USE_VALGRIND */
 101 }
 102
 103 pdns_ucontext_t::~pdns_ucontext_t() {
 104     delete static_cast<ucontext_t*>(uc_mcontext);
 105 #ifdef PDNS_USE_VALGRIND
 106     if (valgrind_id != 0) {
 107       VALGRIND_STACK_DEREGISTER(valgrind_id);
 108     }
 109 #endif /* PDNS_USE_VALGRIND */
 110 }
 111
 112 void
 113 pdns_swapcontext
 114 (pdns_ucontext_t& __restrict octx, pdns_ucontext_t const& __restrict ctx) {
 115     if (::swapcontext (static_cast<ucontext_t*>(octx.uc_mcontext),
 116                        static_cast<ucontext_t*>(ctx.uc_mcontext))) {
 117         throw_errno ("swapcontext() failed");
 118     }
 119     if (ctx.exception) {
 120         std::rethrow_exception (ctx.exception);
 121     }
 122 }
 123
 124 void
 125 pdns_makecontext
 126 (pdns_ucontext_t& ctx, boost::function<void(void)>& start) {
 127     assert (ctx.uc_link);
 128     assert (ctx.uc_stack.size());
 129
 130     auto const mcp = static_cast<ucontext_t*>(ctx.uc_mcontext);
 131     auto const next = static_cast<ucontext_t*>(ctx.uc_link->uc_mcontext);
 132     if (::getcontext (mcp)) {
 133         throw_errno ("getcontext() failed");
 134     }
 135     mcp->uc_link = next;
 136     mcp->uc_stack.ss_sp = ctx.uc_stack.data();
 137     mcp->uc_stack.ss_size = ctx.uc_stack.size()-1;
 138     mcp->uc_stack.ss_flags = 0;
 139
 140     auto ctxarg = splitPointer (&ctx);
 141     auto funarg = splitPointer (&start);
 142     return ::makecontext (mcp, reinterpret_cast<void(*)(void)>(&threadWrapper),
 143                           4, ctxarg.first, ctxarg.second,
 144                           funarg.first, funarg.second);
 145 }