Index: clang/lib/Driver/ToolChains/AVR.cpp
===================================================================
--- clang/lib/Driver/ToolChains/AVR.cpp
+++ clang/lib/Driver/ToolChains/AVR.cpp
@@ -497,14 +497,6 @@
       D.Diag(diag::warn_drv_avr_stdlib_not_linked);
   }
 
-  if (SectionAddressData) {
-    CmdArgs.push_back(Args.MakeArgString(
-        "-Tdata=0x" + Twine::utohexstr(*SectionAddressData)));
-  } else {
-    // We do not have an entry for this CPU in the address mapping table yet.
-    D.Diag(diag::warn_drv_avr_linker_section_addresses_not_implemented) << CPU;
-  }
-
   // If the family name is known, we can link with the device-specific libgcc.
   // Without it, libgcc will simply not be linked. This matches avr-gcc
   // behavior.
@@ -542,8 +534,23 @@
 
     CmdArgs.push_back("--end-group");
 
-    // Add user specified linker script.
-    Args.AddAllArgs(CmdArgs, options::OPT_T);
+    // If user explicitly specifies a linker script via '-T', we should follow.
+    // Otherwise we must add a default '-Tdata' option to the linker, according
+    // to each AVR device's specific memory layout.
+    // TODO: Use the default linker script provided by avr-libc, which can be
+    // overwritten if user specifies via '-T' or '-Wl,-T'.
+    if (!Args.hasArg(options::OPT_T)) {
+      if (SectionAddressData) {
+        CmdArgs.push_back(Args.MakeArgString(
+            "-Tdata=0x" + Twine::utohexstr(*SectionAddressData)));
+      } else {
+        // We do not have an entry for this CPU in the address mapping table yet.
+        D.Diag(diag::warn_drv_avr_linker_section_addresses_not_implemented) << CPU;
+      }
+    } else {
+      // Add user specified linker script.
+      Args.AddAllArgs(CmdArgs, options::OPT_T);
+    }
 
     // Specify the family name as the emulation mode to use.
     // This is almost always required because otherwise avr-ld
Index: clang/test/Driver/avr-ld.c
===================================================================
--- clang/test/Driver/avr-ld.c
+++ clang/test/Driver/avr-ld.c
@@ -1,44 +1,52 @@
 // RUN: %clang -### --target=avr -mmcu=at90s2313 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKA %s
-// LINKA: {{".*ld.*"}} {{.*}} {{"-L.*tiny-stack"}} {{.*}} "-Tdata=0x800060" "--start-group" {{.*}} "-lat90s2313" {{.*}} "--end-group" "-mavr2"
+// LINKA: {{".*ld.*"}} {{.*}} {{"-L.*tiny-stack"}} {{.*}} "--start-group" {{.*}} "-lat90s2313" {{.*}} "--end-group" "-Tdata=0x800060" "-mavr2"
 
 // RUN: %clang -### --target=avr -mmcu=at90s8515 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKB %s
-// LINKB: {{".*ld.*"}} {{.*}} "-Tdata=0x800060" "--start-group" {{.*}} "-lat90s8515" {{.*}} "--end-group" "-mavr2"
+// LINKB: {{".*ld.*"}} {{.*}} "--start-group" {{.*}} "-lat90s8515" {{.*}} "--end-group" "-Tdata=0x800060" "-mavr2"
 
 // RUN: %clang -### --target=avr -mmcu=attiny13 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKC %s
-// LINKC: {{".*ld.*"}} {{.*}} {{"-L.*avr25/tiny-stack"}} {{.*}} "-Tdata=0x800060" "--start-group" {{.*}} "-lattiny13" {{.*}} "--end-group" "-mavr25"
+// LINKC: {{".*ld.*"}} {{.*}} {{"-L.*avr25/tiny-stack"}} {{.*}} "--start-group" {{.*}} "-lattiny13" {{.*}} "--end-group" "-Tdata=0x800060" "-mavr25"
 
 // RUN: %clang -### --target=avr -mmcu=attiny44 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKD %s
-// LINKD: {{".*ld.*"}} {{.*}} {{"-L.*avr25"}} {{.*}} "-Tdata=0x800060" "--start-group" {{.*}} "-lattiny44" {{.*}} "--end-group" "-mavr25"
+// LINKD: {{".*ld.*"}} {{.*}} {{"-L.*avr25"}} {{.*}} "--start-group" {{.*}} "-lattiny44" {{.*}} "--end-group" "-Tdata=0x800060" "-mavr25"
 
 // RUN: %clang -### --target=avr -mmcu=atmega103 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKE %s
-// LINKE: {{".*ld.*"}} {{.*}} {{"-L.*avr31"}} {{.*}} "-Tdata=0x800060" "--start-group" {{.*}} "-latmega103" {{.*}} "--end-group" "-mavr31"
+// LINKE: {{".*ld.*"}} {{.*}} {{"-L.*avr31"}} {{.*}} "--start-group" {{.*}} "-latmega103" {{.*}} "--end-group" "-Tdata=0x800060" "-mavr31"
 
 // RUN: %clang -### --target=avr -mmcu=atmega8u2 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKF %s
-// LINKF: {{".*ld.*"}} {{.*}} {{"-L.*avr35"}} {{.*}} "-Tdata=0x800100" "--start-group" {{.*}} "-latmega8u2" {{.*}} "--end-group" "-mavr35"
+// LINKF: {{".*ld.*"}} {{.*}} {{"-L.*avr35"}} {{.*}} "--start-group" {{.*}} "-latmega8u2" {{.*}} "--end-group" "-Tdata=0x800100" "-mavr35"
 
 // RUN: %clang -### --target=avr -mmcu=atmega48pa --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKG %s
-// LINKG: {{".*ld.*"}} {{.*}} {{"-L.*avr4"}} {{.*}} "-Tdata=0x800100" "--start-group" {{.*}} "-latmega48pa" {{.*}} "--end-group" "-mavr4"
+// LINKG: {{".*ld.*"}} {{.*}} {{"-L.*avr4"}} {{.*}} "--start-group" {{.*}} "-latmega48pa" {{.*}} "--end-group" "-Tdata=0x800100" "-mavr4"
 
 // RUN: %clang -### --target=avr -mmcu=atmega328 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKH %s
-// LINKH: {{".*ld.*"}} {{.*}} {{"-L.*avr5"}} {{.*}} "-Tdata=0x800100" "--start-group" {{.*}} "-latmega328" {{.*}} "--end-group" "-mavr5"
+// LINKH: {{".*ld.*"}} {{.*}} {{"-L.*avr5"}} {{.*}} "--start-group" {{.*}} "-latmega328" {{.*}} "--end-group" "-Tdata=0x800100" "-mavr5"
 
 // RUN: %clang -### --target=avr -mmcu=atmega1281 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKI %s
-// LINKI: {{".*ld.*"}} {{.*}} {{"-L.*avr51"}} {{.*}} "-Tdata=0x800200" "--start-group" {{.*}} "-latmega1281" {{.*}} "--end-group" "-mavr51"
+// LINKI: {{".*ld.*"}} {{.*}} {{"-L.*avr51"}} {{.*}} "--start-group" {{.*}} "-latmega1281" {{.*}} "--end-group" "-Tdata=0x800200" "-mavr51"
 
 // RUN: %clang -### --target=avr -mmcu=atmega2560 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKJ %s
-// LINKJ: {{".*ld.*"}} {{.*}} {{"-L.*avr6"}} {{.*}} "-Tdata=0x800200" "--start-group" {{.*}} "-latmega2560" {{.*}} "--end-group" "-mavr6"
+// LINKJ: {{".*ld.*"}} {{.*}} {{"-L.*avr6"}} {{.*}} "--start-group" {{.*}} "-latmega2560" {{.*}} "--end-group" "-Tdata=0x800200" "-mavr6"
 
 // RUN: %clang -### --target=avr -mmcu=attiny10 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKK %s
-// LINKK: {{".*ld.*"}} {{.*}} {{"-L.*avrtiny"}} {{.*}} "-Tdata=0x800040" "--start-group" {{.*}} "-lattiny10" {{.*}} "--end-group" "-mavrtiny"
+// LINKK: {{".*ld.*"}} {{.*}} {{"-L.*avrtiny"}} {{.*}} "--start-group" {{.*}} "-lattiny10" {{.*}} "--end-group" "-Tdata=0x800040" "-mavrtiny"
 
 // RUN: %clang -### --target=avr -mmcu=atxmega16a4 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKL %s
-// LINKL: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega2"}} {{.*}} "-Tdata=0x802000" "--start-group" {{.*}} "-latxmega16a4" {{.*}} "--end-group" "-mavrxmega2"
+// LINKL: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega2"}} {{.*}} "--start-group" {{.*}} "-latxmega16a4" {{.*}} "--end-group" "-Tdata=0x802000" "-mavrxmega2"
 
 // RUN: %clang -### --target=avr -mmcu=atxmega64b3 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKM %s
-// LINKM: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega4"}} {{.*}} "-Tdata=0x802000" "--start-group" {{.*}} "-latxmega64b3" {{.*}} "--end-group" "-mavrxmega4"
+// LINKM: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega4"}} {{.*}} "--start-group" {{.*}} "-latxmega64b3" {{.*}} "--end-group" "-Tdata=0x802000" "-mavrxmega4"
 
 // RUN: %clang -### --target=avr -mmcu=atxmega128a3u --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKN %s
-// LINKN: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega6"}} {{.*}} "-Tdata=0x802000" "--start-group" {{.*}} "-latxmega128a3u" {{.*}} "--end-group" "-mavrxmega6"
+// LINKN: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega6"}} {{.*}} "--start-group" {{.*}} "-latxmega128a3u" {{.*}} "--end-group" "-Tdata=0x802000" "-mavrxmega6"
 
 // RUN: %clang -### --target=avr -mmcu=atxmega128a1 --rtlib=libgcc --sysroot %S/Inputs/basic_avr_tree %s 2>&1 | FileCheck -check-prefix LINKO %s
-// LINKO: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega7"}} {{.*}} "-Tdata=0x802000" "--start-group" {{.*}} "-latxmega128a1" {{.*}} "--end-group" "-mavrxmega7"
+// LINKO: {{".*ld.*"}} {{.*}} {{"-L.*avrxmega7"}} {{.*}} "--start-group" {{.*}} "-latxmega128a1" {{.*}} "--end-group" "-Tdata=0x802000" "-mavrxmega7"
+
+// RUN: %clang -### --target=avr -mmcu=atmega8u2 --sysroot %S/Inputs/basic_avr_tree %s -T %S/Inputs/basic_avr_tree/usr/lib/avr/lib/avr35.lds 2>&1 | FileCheck -check-prefix LINKP %s
+// LINKP: {{".*ld.*"}} {{.*}} {{"-L.*avr35"}} {{.*}} "--start-group" {{.*}} "-latmega8u2" {{.*}} "--end-group" "-T" {{".*avr35.lds"}} "-mavr35"
+// LINKP-NOT: "-Tdata"
+
+// RUN: %clang -### --target=avr --sysroot %S/Inputs/basic_avr_tree %s -T %S/Inputs/basic_avr_tree/usr/lib/avr/lib/avr51.lds 2>&1 | FileCheck -check-prefix LINKQ %s
+// LINKQ-NOT: "-Tdata"
+// LINKQ-NOT: "warning:" {{.*}} "section address"
Index: clang/test/Driver/avr-toolchain.c
===================================================================
--- clang/test/Driver/avr-toolchain.c
+++ clang/test/Driver/avr-toolchain.c
@@ -7,8 +7,8 @@
 // CHECK1-SAME: "-isysroot" "[[SYSROOT:[^"]+/basic_avr_tree]]"
 // CHECK1-SAME: "-internal-isystem"
 // CHECK1-SAME: {{^}} "[[SYSROOT]]/usr/lib/gcc/avr/5.4.0/../../../avr/include"
-// CHECK1-NOT:  "-L
-// CHECK1:      avr-ld"
+// CHECK1-NOT:  "-L"
+// CHECK1:      {{".*avr-ld"}}
 // CHECK1-SAME: "-o" "a.out"
 // CHECK1-SAME: {{^}} "--gc-sections"
 
@@ -46,7 +46,6 @@
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree %s 2>&1 | FileCheck --check-prefixes=NOMCU,LINKB %s
 // NOMCU: warning: no target microcontroller specified on command line, cannot link standard libraries, please pass -mmcu=<mcu name>
 // LINKB: warning: standard library not linked and so no interrupt vector table or compiler runtime routines will be linked
-// LINKB: warning: support for passing the data section address to the linker for microcontroller '' is not implemented
 // NOMCU-NOT: warning: {{.*}} avr-gcc
 // NOMCU-NOT: warning: {{.*}} avr-libc
 // LINKA-NOT: warning: {{.*}} interrupt vector