[kvm-unit-tests PATCH v3 3/5] configure: Support cross compiling with clang

[Andrew Jones]

When a user specifies the compiler with --cc assume it's already
fully named, even if the user also specifies a cross-prefix. This
allows clang to be selected for the compiler, which doesn't use
prefixes, but also still provide a cross prefix for binutils. If
a user needs a prefix on the compiler that they specify with --cc,
then they'll just have to specify it with the prefix prepended.

Also ensure user provided cflags are used when testing the compiler,
since the flags may drastically change behavior, such as the --target
flag for clang.

With these changes it's possible to cross compile for riscv with
clang after configuring with

 ./configure --arch=riscv64 --cc=clang --cflags='--target=riscv64' \
             --cross-prefix=riscv64-linux-gnu-

Reviewed-by: Thomas Huth <thuth at redhat.com>
Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
Signed-off-by: Andrew Jones <andrew.jones at linux.dev>
---
 configure | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index 27ae9cc89657..337af07374df 100755
--- a/configure
+++ b/configure
@@ -130,6 +130,7 @@ while [[ "$1" = -* ]]; do
 	    ;;
 	--cc)
 	    cc="$arg"
+	    cc_selected=yes
 	    ;;
 	--cflags)
 	    cflags="$arg"
@@ -200,6 +201,10 @@ while [[ "$1" = -* ]]; do
     esac
 done
 
+if [ -z "$cc_selected" ] && [ "$cross_prefix" ]; then
+    cc="$cross_prefix$cc"
+fi
+
 if [ -z "$efi" ] || [ "$efi" = "n" ]; then
     [ "$efi_direct" = "y" ] && efi_direct=
 fi
@@ -370,7 +375,7 @@ fi
 cat << EOF > lib-test.c
 __UINT32_TYPE__
 EOF
-u32_long=$("$cross_prefix$cc" -E lib-test.c | grep -v '^#' | grep -q long && echo yes)
+u32_long=$("$cc" $cflags -E lib-test.c | grep -v '^#' | grep -q long && echo yes)
 rm -f lib-test.c
 
 # check if slash can be used for division
@@ -379,7 +384,7 @@ if [ "$arch" = "i386" ] || [ "$arch" = "x86_64" ]; then
 foo:
     movl (8 / 2), %eax
 EOF
-  wa_divide=$("$cross_prefix$cc" -c lib-test.S >/dev/null 2>&1 || echo yes)
+  wa_divide=$("$cc" $cflags -c lib-test.S >/dev/null 2>&1 || echo yes)
   rm -f lib-test.{o,S}
 fi
 
@@ -442,7 +447,7 @@ ARCH=$arch
 ARCH_NAME=$arch_name
 ARCH_LIBDIR=$arch_libdir
 PROCESSOR=$processor
-CC=$cross_prefix$cc
+CC=$cc
 CFLAGS=$cflags
 LD=$cross_prefix$ld
 OBJCOPY=$cross_prefix$objcopy
-- 
2.46.0