Generate gdb indexing for faster debugging on Linux

If the linker supports it, add the gdb index to the debug symbols, which
makes loading gdb on Qt libraries much faster.

Change-Id: I2ed201c22913b97ac2efaefb5e31636e795ae102
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

configure.json

@@ -307,6 +307,11 @@
             "type": "linkerSupportsFlag",
             "flag": "--enable-new-dtags"
         },
+        "gdb_index": {
+            "label": "gdb index support",
+            "type": "linkerSupportsFlag",
+            "flag": "--gdb-index"
+        },
         "reduce_exports": {
             "label": "symbol visibility support",
             "type": "compile",
@@ -813,6 +818,12 @@
             "condition": "config.linux && tests.enable_new_dtags",
             "output": [ "privateConfig" ]
         },
+        "enable_gdb_index": {
+            "label": "Generating GDB index",
+            "autoDetect": "features.developer-build",
+            "condition": "config.gcc && !config.clang && (features.debug || features.force_debug_info || features.debug_and_release) && tests.gdb_index",
+            "output": [ "privateConfig" ]
+        },
         "reduce_exports": {
             "label": "Reduce amount of exported symbols",
             "condition": "!config.win32 && tests.reduce_exports",
@@ -1265,6 +1276,11 @@ Configure with '-qreal float' to create a build that is binary-compatible with 5
                     "args": "enable_new_dtags",
                     "condition": "config.linux"
                 },
+                {
+                    "type": "feature",
+                    "args": "enable_gdb_index",
+                    "condition": "config.gcc && !config.clang && (features.debug || features.force_debug_info || features.debug_and_release)"
+                },
                 "precompile_header",
                 "ltcg",
                 {

mkspecs/common/gcc-base-unix.conf

@@ -19,6 +19,7 @@ QMAKE_LFLAGS_THREAD    +=
 QMAKE_LFLAGS_RPATH      = -Wl,-rpath,
 QMAKE_LFLAGS_RPATHLINK  = -Wl,-rpath-link,
 QMAKE_LFLAGS_NEW_DTAGS  = -Wl,--enable-new-dtags
+QMAKE_LFLAGS_GDB_INDEX  = -Wl,--gdb-index
 QMAKE_LFLAGS_USE_GOLD   = -fuse-ld=gold
 
 # -Bsymbolic-functions (ld) support

mkspecs/features/default_post.prf

@@ -80,6 +80,7 @@ stack_protector_strong {
 !host_build|!cross_compile {
     use_gold_linker: QMAKE_LFLAGS += $$QMAKE_LFLAGS_USE_GOLD
     enable_new_dtags: QMAKE_LFLAGS += $$QMAKE_LFLAGS_NEW_DTAGS
+    enable_gdb_index: QMAKE_LFLAGS += $$QMAKE_LFLAGS_GDB_INDEX
 }
 
 dll:win32: QMAKE_LFLAGS += $$QMAKE_LFLAGS_DLL