Merge bitcoin#18088: build: ensure we aren't using GNU extensions

0ae8f18 build: add -Wgnu to compile flags (fanquake)
3a0fd77 Remove use of non-standard zero variadic macros (Ben Woosley)
49f6178 Drop unused LOG_TIME_MICROS helper (Ben Woosley)
5d49999 prevector: Avoid unnamed struct, which is a GNU extension (DesWurstes)

Pull request description:

  Since we [started using](bitcoin#7165) the `ax_cxx_compile_stdcxx.m4` macro we've been passing `[noext]` to indicate that we don't want to use an extended mode, i.e GNU extensions. Speaking to Cory he clarified that the intention was to "require only vanilla c++11 and turn _off_ extension support so they would fail to compile".

  However in the codebase we are currently making use of some GNU extensions. We should either remove there usage, or at least amend our CXX compiler checks. I'd prefer the former.

  #### anonymous structs
  ```bash
  ./prevector.h:153:9: warning: anonymous structs are a GNU extension [-Wgnu-anonymous-struct]
          struct {
  ```

  This is fixed in bitcoin@b849212.

  #### variadic macros

  ```bash
  ./undo.h:57:50: warning: must specify at least one argument for '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments]
              ::Unserialize(s, VARINT(nVersionDummy));
  ```

  This is taken care of in bitcoin#18087.

  The `LOG_TIME_*` macros introduced in bitcoin#16805 make use of a [GNU extension](https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html).

  ```bash
  In file included from validation.cpp:22:
  ./logging/timer.h:99:99: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
      BCLog::Timer<std::chrono::milliseconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg, ## __VA_ARGS__)
                                                                                                    ^
  ./logging/timer.h:99:99: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
  ./logging/timer.h:99:99: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
  ./logging/timer.h:99:99: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
  ./logging/timer.h:99:99: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
  ./logging/timer.h:101:92: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
      BCLog::Timer<std::chrono::seconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg, ## __VA_ARGS__)
                                                                                             ^
  6 warnings generated.
  ```

  This is fixed in 081a0ab and 612e8e1.

  #### prevention
  To ensure that usage doesn't creep back in we can add [`-Wgnu`](https://clang.llvm.org/docs/DiagnosticsReference.html#wgnu) to our compile time flags, which will make Clang warn whenever it encounters GNU extensions.

  This would close bitcoin#14130.
  Also related to bitcoin#17230, where it's suggested we use a GNU extension, the `gnu::pure` attribute.

ACKs for top commit:
  practicalswift:
    ACK 0ae8f18 -- diff looks correct
  MarcoFalke:
    ACK 0ae8f18
  vasild:
    utACK 0ae8f18
  dongcarl:
    ACK 0ae8f18

Tree-SHA512: c517404681ef8edf04c785731d26105bac9f3c9c958605aa24cbe399c649e7c5ee0c4aa8e714fd2b2d335e2fbea4d571e09b0dec36678ef871f0a6683ba6bb7f

Author: fanquake

configure.ac

@@ -349,6 +349,7 @@ fi
 if test "x$CXXFLAGS_overridden" = "xno"; then
   AX_CHECK_COMPILE_FLAG([-Wall],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wall"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wextra],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wextra"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wgnu],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wgnu"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wformat],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wformat"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wvla],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wvla"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wswitch],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wswitch"],,[[$CXXFLAG_WERROR]])

src/logging/timer.h

@@ -93,12 +93,10 @@ class Timer
 } // namespace BCLog
 
 
-#define LOG_TIME_MICROS(end_msg, ...) \
-    BCLog::Timer<std::chrono::microseconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg, ## __VA_ARGS__)
-#define LOG_TIME_MILLIS(end_msg, ...) \
-    BCLog::Timer<std::chrono::milliseconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg, ## __VA_ARGS__)
-#define LOG_TIME_SECONDS(end_msg, ...) \
-    BCLog::Timer<std::chrono::seconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg, ## __VA_ARGS__)
+#define LOG_TIME_MILLIS_WITH_CATEGORY(end_msg, log_category) \
+    BCLog::Timer<std::chrono::milliseconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg, log_category)
+#define LOG_TIME_SECONDS(end_msg) \
+    BCLog::Timer<std::chrono::seconds> PASTE2(logging_timer, __COUNTER__)(__func__, end_msg)
 
 
 #endif // BITCOIN_LOGGING_TIMER_H

src/prevector.h

@@ -152,7 +152,7 @@ class prevector {
         struct {
             char* indirect;
             size_type capacity;
-        };
+        } indirect_contents;
     };
 #pragma pack(pop)
     alignas(char*) direct_or_indirect _union = {};
@@ -163,8 +163,8 @@ class prevector {
 
     T* direct_ptr(difference_type pos) { return reinterpret_cast<T*>(_union.direct) + pos; }
     const T* direct_ptr(difference_type pos) const { return reinterpret_cast<const T*>(_union.direct) + pos; }
-    T* indirect_ptr(difference_type pos) { return reinterpret_cast<T*>(_union.indirect) + pos; }
-    const T* indirect_ptr(difference_type pos) const { return reinterpret_cast<const T*>(_union.indirect) + pos; }
+    T* indirect_ptr(difference_type pos) { return reinterpret_cast<T*>(_union.indirect_contents.indirect) + pos; }
+    const T* indirect_ptr(difference_type pos) const { return reinterpret_cast<const T*>(_union.indirect_contents.indirect) + pos; }
     bool is_direct() const { return _size <= N; }
 
     void change_capacity(size_type new_capacity) {
@@ -182,17 +182,17 @@ class prevector {
                 /* FIXME: Because malloc/realloc here won't call new_handler if allocation fails, assert
                     success. These should instead use an allocator or new/delete so that handlers
                     are called as necessary, but performance would be slightly degraded by doing so. */
-                _union.indirect = static_cast<char*>(realloc(_union.indirect, ((size_t)sizeof(T)) * new_capacity));
-                assert(_union.indirect);
-                _union.capacity = new_capacity;
+                _union.indirect_contents.indirect = static_cast<char*>(realloc(_union.indirect_contents.indirect, ((size_t)sizeof(T)) * new_capacity));
+                assert(_union.indirect_contents.indirect);
+                _union.indirect_contents.capacity = new_capacity;
             } else {
                 char* new_indirect = static_cast<char*>(malloc(((size_t)sizeof(T)) * new_capacity));
                 assert(new_indirect);
                 T* src = direct_ptr(0);
                 T* dst = reinterpret_cast<T*>(new_indirect);
                 memcpy(dst, src, size() * sizeof(T));
-                _union.indirect = new_indirect;
-                _union.capacity = new_capacity;
+                _union.indirect_contents.indirect = new_indirect;
+                _union.indirect_contents.capacity = new_capacity;
                 _size += N + 1;
             }
         }
@@ -301,7 +301,7 @@ class prevector {
         if (is_direct()) {
             return N;
         } else {
-            return _union.capacity;
+            return _union.indirect_contents.capacity;
         }
     }
 
@@ -468,8 +468,8 @@ class prevector {
             clear();
         }
         if (!is_direct()) {
-            free(_union.indirect);
-            _union.indirect = nullptr;
+            free(_union.indirect_contents.indirect);
+            _union.indirect_contents.indirect = nullptr;
         }
     }
 
@@ -521,7 +521,7 @@ class prevector {
         if (is_direct()) {
             return 0;
         } else {
-            return ((size_t)(sizeof(T))) * _union.capacity;
+            return ((size_t)(sizeof(T))) * _union.indirect_contents.capacity;
         }
     }
 

src/validation.cpp

@@ -2279,11 +2279,11 @@ bool CChainState::FlushStateToDisk(
         LOCK(cs_LastBlockFile);
         if (fPruneMode && (fCheckForPruning || nManualPruneHeight > 0) && !fReindex) {
             if (nManualPruneHeight > 0) {
-                LOG_TIME_MILLIS("find files to prune (manual)", BCLog::BENCH);
+                LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune (manual)", BCLog::BENCH);
 
                 FindFilesToPruneManual(setFilesToPrune, nManualPruneHeight);
             } else {
-                LOG_TIME_MILLIS("find files to prune", BCLog::BENCH);
+                LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune", BCLog::BENCH);
 
                 FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight());
                 fCheckForPruning = false;
@@ -2321,15 +2321,15 @@ bool CChainState::FlushStateToDisk(
                 return AbortNode(state, "Disk space is too low!", _("Error: Disk space is too low!").translated, CClientUIInterface::MSG_NOPREFIX);
             }
             {
-                LOG_TIME_MILLIS("write block and undo data to disk", BCLog::BENCH);
+                LOG_TIME_MILLIS_WITH_CATEGORY("write block and undo data to disk", BCLog::BENCH);
 
                 // First make sure all block and undo data is flushed to disk.
                 FlushBlockFile();
             }
 
             // Then update all block file information (which may refer to block and undo files).
             {
-                LOG_TIME_MILLIS("write block index to disk", BCLog::BENCH);
+                LOG_TIME_MILLIS_WITH_CATEGORY("write block index to disk", BCLog::BENCH);
 
                 std::vector<std::pair<int, const CBlockFileInfo*> > vFiles;
                 vFiles.reserve(setDirtyFileInfo.size());
@@ -2349,7 +2349,7 @@ bool CChainState::FlushStateToDisk(
             }
             // Finally remove any pruned files
             if (fFlushForPrune) {
-                LOG_TIME_MILLIS("unlink pruned files", BCLog::BENCH);
+                LOG_TIME_MILLIS_WITH_CATEGORY("unlink pruned files", BCLog::BENCH);
 
                 UnlinkPrunedFiles(setFilesToPrune);
             }