misc: Updates for gcc7.2 for x86

GCC 7.2 is much stricter than previous GCC versions. The following changes
are needed:

* There is now a warning if there is an implicit fallthrough between two
  case statments. C++17 adds the [[fallthrough]]; declaration. However,
  to support non C++17 standards (i.e., C++11), we use M5_FALLTHROUGH.
  M5_FALLTHROUGH checks for [[fallthrough]] compliant C++17 compiler and
  if that doesn't exist, it defaults to nothing (no older compilers
  generate warnings).
* The above resulted in a couple of bugs that were found. This is noted
  in the review request on gerrit.
* throw() for dynamic exception specification is deprecated
* There were a couple of new uninitialized variable warnings
* Can no longer perform bitwise operations on a bool.
* Must now include <functional> for std::function
* Compiler bug for void* lambda. Changed to auto as work around. See
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82878

Change-Id: I5d4c782a4e133fa4cdb119e35d9aff68c6e2958e
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5802
Reviewed-by: Gabe Black <gabeblack@google.com>

3 files changed, 21 insertions, 1 deletions

diff --git a/src/base/compiler.hh b/src/base/compiler.hh
index 2fdd323b9..6920dad10 100644
--- a/src/base/compiler.hh
+++ b/src/base/compiler.hh
@@ -63,6 +63,20 @@
 #  define M5_CLASS_VAR_USED
 #endif
 
+// This can be removed once all compilers support C++17
+#if defined __has_cpp_attribute
+    // Note: We must separate this if statement because GCC < 5.0 doesn't
+    //       support the function-like syntax in #if statements.
+    #if __has_cpp_attribute(fallthrough)
+        #define M5_FALLTHROUGH [[fallthrough]]
+    #else
+        #define M5_FALLTHROUGH
+    #endif
+#else
+    // Unsupported (and no warning) on GCC < 7.
+    #define M5_FALLTHROUGH
+#endif
+
 // std::make_unique redefined for C++11 compilers
 namespace m5
 {
diff --git a/src/base/cprintf.cc b/src/base/cprintf.cc
index 5daf196f1..caf1bb847 100644
--- a/src/base/cprintf.cc
+++ b/src/base/cprintf.cc
@@ -35,6 +35,8 @@
 #include <iostream>
 #include <sstream>
 
+#include "base/compiler.hh"
+
 using namespace std;
 
 namespace cp {
@@ -138,6 +140,7 @@ Print::process_flag()
 
           case 'X':
             fmt.uppercase = true;
+            M5_FALLTHROUGH;
           case 'x':
             fmt.base = Format::hex;
             fmt.format = Format::integer;
@@ -159,6 +162,7 @@ Print::process_flag()
 
           case 'G':
             fmt.uppercase = true;
+            M5_FALLTHROUGH;
           case 'g':
             fmt.format = Format::floating;
             fmt.float_format = Format::best;
@@ -167,6 +171,7 @@ Print::process_flag()
 
           case 'E':
             fmt.uppercase = true;
+            M5_FALLTHROUGH;
           case 'e':
             fmt.format = Format::floating;
             fmt.float_format = Format::scientific;
@@ -213,6 +218,7 @@ Print::process_flag()
                 fmt.fill_zero = true;
                 break;
             }
+            M5_FALLTHROUGH;
           case '1':
           case '2':
           case '3':
diff --git a/src/base/imgwriter.cc b/src/base/imgwriter.cc
index 40de3d7cc..13ff86c30 100644
--- a/src/base/imgwriter.cc
+++ b/src/base/imgwriter.cc
@@ -59,7 +59,7 @@ createImgWriter(Enums::ImageFormat type, const FrameBuffer *fb)
         // gem5 will try PNG first, and it will fallback to BMP if not
         // available.
 
-        /* FALLTHROUGH */
+        M5_FALLTHROUGH;
 #if USE_PNG
       case Enums::Png:
         return std::unique_ptr<PngWriter>(new PngWriter(fb));