diff --git a/config/BUILDCONFIG.gn b/config/BUILDCONFIG.gn
index 8811465da..643ded82c 100644
--- a/config/BUILDCONFIG.gn
+++ b/config/BUILDCONFIG.gn
@@ -359,7 +359,6 @@ if (is_win) {
   _native_compiler_configs += [
     "//build/config/win:lean_and_mean",
     "//build/config/win:nominmax",
-    "//build/config/win:sdk",
     "//build/config/win:unicode",
     "//build/config/win:winver",
   ]
@@ -375,16 +374,6 @@ if (is_posix) {
   ]
 }
 
-if (is_linux) {
-  _native_compiler_configs += [ "//build/config/linux:sdk" ]
-} else if (is_mac) {
-  _native_compiler_configs += [ "//build/config/mac:sdk" ]
-} else if (is_ios) {
-  _native_compiler_configs += [ "//build/config/ios:sdk" ]
-} else if (is_android) {
-  _native_compiler_configs += [ "//build/config/android:sdk" ]
-}
-
 if (is_android) {
   _native_compiler_configs +=
       [ "//build/config/android:default_cygprofile_instrumentation" ]
diff --git a/config/android/BUILD.gn b/config/android/BUILD.gn
index 0503bef1e..618d0961e 100644
--- a/config/android/BUILD.gn
+++ b/config/android/BUILD.gn
@@ -195,23 +195,6 @@ config("runtime_library") {
   }
 }
 
-config("sdk") {
-  if (sysroot != "") {
-    cflags = [ "--sysroot=" + sysroot ]
-    asmflags = [ "--sysroot=" + sysroot ]
-    ldflags = [ "--sysroot=" + sysroot ]
-
-    # Need to get some linker flags out of the sysroot.
-    sysroot_ld_path = rebase_path("//build/config/linux/sysroot_ld_path.py")
-    ldflags += [ exec_script(sysroot_ld_path,
-                             [
-                               rebase_path("//build/linux/sysroot_ld_path.sh"),
-                               sysroot,
-                             ],
-                             "value") ]
-  }
-}
-
 config("executable_config") {
   cflags = [ "-fPIE" ]
   asmflags = [ "-fPIE" ]
diff --git a/config/compiler/BUILD.gn b/config/compiler/BUILD.gn
index ef8fbd418..31815c367 100644
--- a/config/compiler/BUILD.gn
+++ b/config/compiler/BUILD.gn
@@ -493,10 +493,20 @@ config("runtime_library") {
   # smaller.
   if (is_win) {
     configs += [ "//build/config/win:runtime_library" ]
+  } else if (is_linux) {
+    configs += [ "//build/config/linux:runtime_library" ]
+  } else if (is_ios) {
+    configs += [ "//build/config/ios:runtime_library" ]
+  } else if (is_mac) {
+    configs += [ "//build/config/mac:runtime_library" ]
   } else if (is_android) {
     configs += [ "//build/config/android:runtime_library" ]
   }
 
+  if (is_posix) {
+    configs += [ "//build/config/posix:runtime_library" ]
+  }
+
   if (is_component_build) {
     defines += [ "COMPONENT_BUILD" ]
   }
diff --git a/config/ios/BUILD.gn b/config/ios/BUILD.gn
index d69f423a0..07e8a86d9 100644
--- a/config/ios/BUILD.gn
+++ b/config/ios/BUILD.gn
@@ -5,7 +5,11 @@
 import("//build/config/sysroot.gni")
 import("//build/config/ios/ios_sdk.gni")
 
-config("sdk") {
+# This is included by reference in the //build/config/compiler:runtime_library
+# config that is applied to all targets. It is here to separate out the logic
+# that is iOS-only. Please see that target for advice on what should go in
+# :runtime_library vs. :compiler.
+config("runtime_library") {
   common_flags = [
     "-isysroot",
     sysroot,
diff --git a/config/linux/BUILD.gn b/config/linux/BUILD.gn
index 45d1dd59f..e39155c61 100644
--- a/config/linux/BUILD.gn
+++ b/config/linux/BUILD.gn
@@ -7,21 +7,11 @@ import("//build/config/features.gni")
 import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
 
-config("sdk") {
-  if (sysroot != "") {
-    cflags = [ "--sysroot=" + sysroot ]
-    ldflags = [ "--sysroot=" + sysroot ]
-
-    # Need to get some linker flags out of the sysroot.
-    ldflags += [ exec_script("sysroot_ld_path.py",
-                             [
-                               rebase_path("//build/linux/sysroot_ld_path.sh",
-                                           root_build_dir),
-                               sysroot,
-                             ],
-                             "value") ]
-  }
-
+# This is included by reference in the //build/config/compiler:runtime_library
+# config that is applied to all targets. It is here to separate out the logic
+# that is Linux-only. Please see that target for advice on what should go in
+# :runtime_library vs. :compiler.
+config("runtime_library") {
   # Set here because OS_CHROMEOS cannot be autodetected in build_config.h like
   # OS_LINUX and the like.
   if (is_chromeos) {
diff --git a/config/mac/BUILD.gn b/config/mac/BUILD.gn
index 7653b9664..16dc52eb0 100644
--- a/config/mac/BUILD.gn
+++ b/config/mac/BUILD.gn
@@ -5,7 +5,11 @@
 import("//build/config/sysroot.gni")
 import("//build/config/mac/mac_sdk.gni")
 
-config("sdk") {
+# This is included by reference in the //build/config/compiler:runtime_library
+# config that is applied to all targets. It is here to separate out the logic
+# that is Mac-only. Please see that target for advice on what should go in
+# :runtime_library vs. :compiler.
+config("runtime_library") {
   common_flags = [
     "-isysroot",
     sysroot,
diff --git a/config/posix/BUILD.gn b/config/posix/BUILD.gn
new file mode 100644
index 000000000..6f65443d7
--- /dev/null
+++ b/config/posix/BUILD.gn
@@ -0,0 +1,29 @@
+# Copyright 2015 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/sysroot.gni")
+
+assert(is_posix)
+
+# This is included by reference in the //build/config/compiler:runtime_library
+# config that is applied to all targets. It is here to separate out the logic
+# that is Posix-only. Please see that target for advice on what should go in
+# :runtime_library vs. :compiler.
+config("runtime_library") {
+  if (!is_mac && sysroot != "") {
+    # Pass the sysroot to all C compiler variants, the assembler, and linker.
+    cflags = [ "--sysroot=" + sysroot ]
+    asmflags = cflags
+    ldflags = cflags
+
+    # Need to get some linker flags out of the sysroot.
+    ldflags += [ exec_script("sysroot_ld_path.py",
+                             [
+                               rebase_path("//build/linux/sysroot_ld_path.sh",
+                                           root_build_dir),
+                               sysroot,
+                             ],
+                             "value") ]
+  }
+}
diff --git a/config/linux/sysroot_ld_path.py b/config/posix/sysroot_ld_path.py
similarity index 100%
rename from config/linux/sysroot_ld_path.py
rename to config/posix/sysroot_ld_path.py
diff --git a/config/win/BUILD.gn b/config/win/BUILD.gn
index d1f670e9f..daa07741c 100644
--- a/config/win/BUILD.gn
+++ b/config/win/BUILD.gn
@@ -84,6 +84,7 @@ config("compiler") {
 config("runtime_library") {
   cflags = []
 
+  # Defines that set up the CRT.
   defines = [
     "__STD_C",
     "_CRT_RAND_S",
@@ -92,6 +93,20 @@ config("runtime_library") {
     "_SCL_SECURE_NO_DEPRECATE",
   ]
 
+  # Defines that set up the Windows SDK.
+  defines += [
+    "_ATL_NO_OPENGL",
+    "_WINDOWS",
+    "CERT_CHAIN_PARA_HAS_EXTRA_FIELDS",
+    "NTDDI_VERSION=0x06030000",
+    "PSAPI_VERSION=1",
+    "WIN32",
+    "_SECURE_ATL",
+
+    # This is required for ATL to use XP-safe versions of its functions.
+    "_USING_V110_SDK71_",
+  ]
+
   if (is_component_build) {
     # Component mode: dynamic CRT. Since the library is shared, it requires
     # exceptions or will give errors about things not matching, so keep
@@ -120,25 +135,6 @@ config("runtime_library") {
   }
 }
 
-# Compiler setup for the Windows SDK. Applied to all targets.
-config("sdk") {
-  # The include path is the stuff returned by the script.
-  #include_dirs = msvc_config[0]  TODO(brettw) make this work.
-
-  defines = [
-    "_ATL_NO_OPENGL",
-    "_WINDOWS",
-    "CERT_CHAIN_PARA_HAS_EXTRA_FIELDS",
-    "NTDDI_VERSION=0x06030000",
-    "PSAPI_VERSION=1",
-    "WIN32",
-    "_SECURE_ATL",
-
-    # This is required for ATL to use XP-safe versions of its functions.
-    "_USING_V110_SDK71_",
-  ]
-}
-
 # Sets the default Windows build version. This is separated because some
 # targets need to manually override it for their compiles.
 config("winver") {