linux: Improve gdb startup time for debug builds from over 4 minutes to 35s.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
@@ skipping 47 matching lines @@
     # it has, then we don't need to disable 4702 (unreachable code warning).
     # The patch is preapplied to the internal toolchain and hence all bots.
     msvs_xtree_patched = false
   }
 
   # Omit unwind support in official builds to save space.
   # We can use breakpad for these builds.
   exclude_unwind_tables = (is_chrome_branded && is_official_build) ||
                           (is_chromecast && !is_cast_desktop_build && !is_debug)
 
-  # If true, gold linker will save symbol table inside object files.
-  # This speeds up gdb startup by 60%
-  gdb_index = false
-
   # If true, optimize for size. Does not affect windows builds.
   # Linux & Mac favor speed over size.
   # TODO(brettw) it's weird that Mac and desktop Linux are different. We should
   # explore favoring size over speed in this case as well.
   optimize_for_size = is_android || is_ios
 
   # Enable fatal linker warnings. Building Chromium with certain versions
   # of binutils can cause linker warning.
   # See: https://bugs.chromium.org/p/chromium/issues/detail?id=457359
   fatal_linker_warnings = true
@@ skipping 220 matching lines @@
   }
 
   # Linux/Android common flags setup.
   # ---------------------------------
   if (is_linux || is_android) {
     if (use_pic) {
       cflags += [ "-fPIC" ]
       ldflags += [ "-fPIC" ]
     }
 
-    cflags += [ "-pipe" ]  # Use pipes for communicating between sub-processes. Faster.
+    # Use pipes for communicating between sub-processes. Faster.
+    cflags += [ "-pipe" ]
 
     ldflags += [
       "-Wl,-z,noexecstack",
       "-Wl,-z,now",
       "-Wl,-z,relro",
     ]
     if (!using_sanitizer) {
       if (!use_cfi_diag) {
         ldflags += [ "-Wl,-z,defs" ]
       }
@@ skipping 45 matching lines @@
           # saved ~20% of link time.
           # https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/281527606915bb36
           # Only apply this to the target linker, since the host
           # linker might not be gold, but isn't used much anyway.
           "-Wl,--threads",
           "-Wl,--thread-count=4",
         ]
       }
     }
 
-    if (gdb_index) {
-      ldflags += [ "-Wl,--gdb-index" ]
-    }
-
     # TODO(thestig): Make this flag work with GN.
     #if (!is_official_build && !is_chromeos && !(is_asan || is_lsan || is_tsan || is_msan)) {
     #  ldflags += [
     #    "-Wl,--detect-odr-violations",
     #  ]
     #}
   } else if (linux_use_bundled_binutils) {
     # Gold is the default linker for the bundled binutils so we explicitly
     # enable the bfd linker when use_gold is not set.
     ldflags += [ "-fuse-ld=bfd" ]
@@ skipping 1263 matching lines @@
         "-g2",
       ]
     } else {
       cflags = [ "-g2" ]
     }
     if (use_debug_fission) {
       cflags += [ "-gsplit-dwarf" ]
     }
     asmflags = cflags
     ldflags = []
+
+    # TODO(thakis): Figure out if there's a way to make this go for 32-bit,
+    # currently we get "warning:
+    # obj/native_client/src/trusted/service_runtime/sel_asm/nacl_switch_32.o:
+    # DWARF info may be corrupt; offsets in a range list entry are in different
+    # sections" there.  Maybe just a bug in nacl_switch_32.S.
+    if (!is_mac && !is_ios && !is_nacl && target_cpu != "x86") {
+      ldflags += [ "-Wl,--gdb-index" ]
+    }
   }
 }
 
 # Minimal symbols.
 config("minimal_symbols") {
   if (is_win) {
     # Linker symbols for backtraces only.
     cflags = []
     ldflags = [ "/DEBUG" ]
   } else {
     if (is_android) {
       # Breakpad can't handle DWARF 4 symbols properly yet, so use DWARF 3
       # explicitly on android where we are hitting https://crbug.com/638485.
       # The arguments MUST be in this order because of a gcc arg parsing bug.
       cflags = [
         "-gdwarf-3",
         "-g1",
       ]
     } else {
       cflags = [ "-g1" ]
     }
-    if (use_debug_fission) {
-      cflags += [ "-gsplit-dwarf" ]
-    }
+
+    # Note: -gsplit-dwarf implicitly turns on -g2 with clang, so don't pass it.
     asmflags = cflags
     ldflags = []
   }
 }
 
 # No symbols.
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
     asmflags = cflags
@@ skipping 15 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }