[release/2.0.0][ARM32] clang 3.9 as a default for ARM cross build (#11197)

* [ARM32] clang 3.9 as a default for ARM cross build

Use clang 3.9 as a default compiler for ARM cross build

* Both arm and armel will be built using clang 3.9 as a default
* ARM CI will use clang 3.9 as a default
* ARM pipieline build will use clang 3.9 as a default

Signed-off-by: Hyung-Kyu Choi <[email protected]>

* [ARM32] Update docs describing clang-3.9 and ARM cross build

Signed-off-by: Hyung-Kyu Choi <[email protected]>

* [ARM] Check minimum version requirement of clang for ARM cross build

Signed-off-by: Hyung-Kyu Choi <[email protected]>

Author: hqueue

Documentation/building/linux-instructions.md

@@ -18,8 +18,8 @@ Toolchain Setup
 Install the following packages for the toolchain: 
 
 - cmake 
-- llvm-3.5 
-- clang-3.5 
+- llvm-3.5 (llvm-3.9 for ARM cross build)
+- clang-3.5 (clang-3.9 for ARM cross build)
 - lldb-3.6
 - lldb-3.6-dev 
 - libunwind8 
@@ -39,6 +39,14 @@ ellismg@linux:~$ wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-
 ellismg@linux:~$ sudo apt-get update
 ```
 
+If you are going to cross build for ARM, you need llvm-3.9 and clang-3.9 and please add below package source instead for Ubuntu 14.04.
+```
+hqueue@linux:~$ echo "deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-3.9 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+hqueue@linux:~$ wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
+hqueue@linux:~$ sudo apt-get update
+```
+For other version of Debian/Ubuntu, please visit http://apt.llvm.org/.
+
 Then install the packages you need:
 
 ```
@@ -120,6 +128,8 @@ index 1ed3dbf..c643032 100644
 How to enable -O3 optimization level for ARM/Linux
 ==================================================
 
+If you are using clang-3.9, -O3 optimization is enabled as default and you can skip this section.
+If you are using older version of clang, please follow instructions in this section to enable -O3 optimization.
 Currently, we can build coreclr with -O1 flag of clang in release build mode for Linux/ARM without any bugfix of llvm-3.6. This instruction is to enable -O3 optimization level of clang on Linux/ARM by fixing the bug of llvm.
 
 First, download latest version from the clang-3.6/llvm-3.6 upstream: 

build.sh

@@ -118,6 +118,14 @@ check_prereqs()
     # Check presence of CMake on the path
     hash cmake 2>/dev/null || { echo >&2 "Please install cmake before running this script"; exit 1; }
 
+
+    # Minimum required version of clang is version 3.9 for arm/armel cross build
+    if [[ $__CrossBuild == 1 && ("$__BuildArch" == "arm" || "$__BuildArch" == "armel") ]]; then
+        if ! [[ "$__ClangMajorVersion" -gt "3" || ( $__ClangMajorVersion == 3 && $__ClangMinorVersion == 9 ) ]]; then
+            echo "Please install clang3.9 or latest for arm/armel cross build"; exit 1;
+        fi
+    fi
+
     # Check for clang
     hash clang-$__ClangMajorVersion.$__ClangMinorVersion 2>/dev/null ||  hash clang$__ClangMajorVersion$__ClangMinorVersion 2>/dev/null ||  hash clang 2>/dev/null || { echo >&2 "Please install clang-$__ClangMajorVersion.$__ClangMinorVersion before running this script"; exit 1; }
 
@@ -780,8 +788,13 @@ fi
 # Set default clang version
 if [[ $__ClangMajorVersion == 0 && $__ClangMinorVersion == 0 ]]; then
     if [ $__CrossBuild == 1 ]; then
-        __ClangMajorVersion=3
-        __ClangMinorVersion=6
+        if [[ "$__BuildArch" == "arm" || "$__BuildArch" == "armel" ]]; then
+            __ClangMajorVersion=3
+            __ClangMinorVersion=9
+        else
+            __ClangMajorVersion=3
+            __ClangMinorVersion=6
+        fi
     else
         __ClangMajorVersion=3
         __ClangMinorVersion=5

tests/scripts/arm32_ci_script.sh

@@ -289,7 +289,7 @@ function cross_build_coreclr_with_docker {
 
     # Cross building coreclr with rootfs in Docker
     (set +x; echo "Start cross build coreclr for $__buildArch $__linuxCodeName")
-    __buildCmd="./build.sh $__buildArch cross $__verboseFlag $__skipMscorlib $__buildConfig -rebuild clang3.9"
+    __buildCmd="./build.sh $__buildArch cross $__verboseFlag $__skipMscorlib $__buildConfig -rebuild"
     $__dockerCmd $__buildCmd
     sudo chown -R $(id -u -n) ./bin
 }