From 15d9b2515631cedcbd427e4c6de2dd4e7a0bfa36 Mon Sep 17 00:00:00 2001
From: Elvis Pranskevichus <elvis@magic.io>
Date: Sat, 4 Jan 2020 16:03:03 -0500
Subject: [PATCH] GCC LTO Support

---
 build/config/BUILD.gn              |  6 +++++-
 build/config/compiler/BUILD.gn     | 30 ++++++++++++++++++++++--------
 build/config/compiler/compiler.gni |  2 +-
 sandbox/linux/BUILD.gn             |  3 +++
 4 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 514ab7b..f8d36fe 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -260,9 +260,13 @@ config("default_libs") {
   } else if (is_linux) {
     libs = [
       "dl",
-      "pthread",
       "rt",
     ]
+    ldflags = [
+      "-Wl,--no-as-needed",
+      "-lpthread",
+      "-Wl,--as-needed"
+    ]
   }
 }
 
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index a3f21b7..48747f7 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -558,12 +558,13 @@ config("compiler") {
   # TODO(pcc): Make this conditional on is_official_build rather than on gn
   # flags for specific features.
   if (!is_debug && use_thin_lto && is_a_target_toolchain) {
-    assert(use_lld || target_os == "chromeos",
-           "gold plugin only supported with ChromeOS")
-
-    cflags += [ "-flto=thin" ]
+    if (is_clang) {
+      cflags += [ "-flto=thin" ]
+    } else {
+      cflags += [ "-flto=2", "-fno-fat-lto-objects", "-fuse-linker-plugin" ]
+    }
 
-    if (target_os != "chromeos") {
+    if (target_os != "chromeos" && is_clang) {
       cflags += [ "-fsplit-lto-unit" ]
     }
 
@@ -586,7 +587,11 @@ config("compiler") {
         "-mllvm:-import-instr-limit=10",
       ]
     } else {
-      ldflags += [ "-flto=thin" ]
+      if (is_clang) {
+        ldflags += [ "-flto=thin" ]
+      } else {
+        ldflags += [ "-flto=8", "-fno-fat-lto-objects", "-fuse-linker-plugin" ]
+      }
 
       # Limit the parallelism to avoid too aggressive competition between
       # linker jobs. This is still suboptimal to a potential dynamic
@@ -607,7 +612,7 @@ config("compiler") {
             "-Wl,--thinlto-cache-policy,$cache_policy",
           ]
         }
-      } else {
+      } else if (is_clang) {
         ldflags += [ "-Wl,-plugin-opt,jobs=8" ]
       }
 
@@ -630,7 +635,7 @@ config("compiler") {
 
     # TODO(pcc): Re-enable this flag on Android. This will require libc++ to be
     # built with ThinLTO (see https://crbug.com/767901) as well as the GVR shim.
-    if (!is_android) {
+    if (!is_android && is_clang) {
       cflags += [ "-fwhole-program-vtables" ]
       if (!is_win) {
         ldflags += [ "-fwhole-program-vtables" ]
@@ -697,6 +702,15 @@ config("compiler") {
   }
 }
 
+config("compiler_no_lto") {
+  cflags = []
+  ldflags = []
+  if (!is_debug && use_thin_lto && is_a_target_toolchain) {
+    cflags += ["-fno-lto"]
+    ldflags += ["-fno-lto"]
+  }
+}
+
 # This provides the basic options to select the target CPU and ABI.
 # It is factored out of "compiler" so that special cases can use this
 # without using everything that "compiler" brings in.  Options that
diff --git a/build/config/compiler/compiler.gni b/build/config/compiler/compiler.gni
index c351d6b..e567372 100644
--- a/build/config/compiler/compiler.gni
+++ b/build/config/compiler/compiler.gni
@@ -57,7 +57,7 @@ declare_args() {
 
   # Enables support for ThinLTO, which links 3x-10x faster than full LTO. See
   # also http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html
-  use_thin_lto = is_cfi || (is_android && is_official_build)
+  use_thin_lto = false
 
   # Tell VS to create a PDB that references information in .obj files rather
   # than copying it all. This should improve linker performance. mspdbcmf.exe
diff --git a/sandbox/linux/BUILD.gn b/sandbox/linux/BUILD.gn
index b00a88c..e4615c0 100644
--- a/sandbox/linux/BUILD.gn
+++ b/sandbox/linux/BUILD.gn
@@ -256,6 +256,9 @@ component("seccomp_bpf") {
     "//base",
     "//base/third_party/dynamic_annotations",
   ]
+  configs += [
+    "//build/config/compiler:compiler_no_lto"
+  ]
 
   if (is_nacl_nonsfi) {
     cflags = [ "-fgnu-inline-asm" ]
-- 
2.24.1