From 255b06005dedd68f7a4cc2ccde3857f4456ecf12 Mon Sep 17 00:00:00 2001
From: Timothy Day <timday@amazon.com>
Date: Sat, 21 Jun 2025 17:36:20 -0400
Subject: Improve LLVM support

Enable $CC to be passed on the build-test-kernel CLI.
Properly set the $LLVM environment variable when using
Clang. This ensures that the full LLVM toolchain is
used (rather than just the compiler).

Signed-off-by: Timothy Day <timday@amazon.com>
---
 build-test-kernel | 11 ++++++++++-
 tests/prelude.sh  |  2 +-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/build-test-kernel b/build-test-kernel
index cd4ff25..b34a20d 100755
--- a/build-test-kernel
+++ b/build-test-kernel
@@ -18,7 +18,7 @@ checkdep bc
 
 ktest_njobs=$(nproc)
 ktest_precise=false
-ktest_compiler=gcc
+ktest_compiler="${CC:-gcc}"
 ktest_skip_kernel_config=false
 
 COVERAGE=""		# doing code coverage?
@@ -122,6 +122,14 @@ run_ktest()
     "$KTEST" "$arg" $KTESTARGS "$@"
 }
 
+map_clang_version() {
+    case "$ktest_compiler" in
+        clang) echo "1" ;;
+        clang-[0-9]*) echo "-${ktest_compiler#clang-}" ;;
+        *) echo "" ;;
+    esac
+}
+
 do_make()
 {
     if [[ -n $CROSS_COMPILE ]]; then
@@ -132,6 +140,7 @@ do_make()
     make --jobs="$ktest_njobs"			\
 	--directory="$ktest_kernel_source"    	\
 	CC="$ktest_compiler"			\
+	LLVM="$(map_clang_version)"		\
 	O="$ktest_kernel_build"			\
 	INSTALL_MOD_PATH="$ktest_kernel_binary"	\
 	"${ktest_kernel_make_append[@]}"	\
diff --git a/tests/prelude.sh b/tests/prelude.sh
index a2b3316..ced9770 100644
--- a/tests/prelude.sh
+++ b/tests/prelude.sh
@@ -34,7 +34,7 @@ if [[ ! -v ktest_cpus ]]; then
     ktest_kernel_config_require=()
     ktest_kernel_config_require_soft=()
     ktest_qemu_append=()
-    ktest_compiler=gcc
+    ktest_compiler="${CC:-gcc}"
     ktest_allow_taint=false
 
     ktest_tests_unknown=false
-- 
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