_setup_env: support Bionic sysroot for USERCFLAGS

This is necessary to support CONFIG_UAPI_HEADER_TEST=y in a build
environment which does not have a cross compiled version of glibc.
Instead, we will use Bionic.

This requires setting the correct path to the prebuilt Bionic headers
and libraries via --sysroot, and using the correct --target= triple,
which differs from what we generally use to cross compile the kernel
itself (which doesn't require a libc).

Bug: 190019968
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: Iac98c377f516ea642cc605ab6d6d3fd022cb20d4

1 files changed, 35 insertions, 2 deletions

diff --git a/_setup_env.sh b/_setup_env.sh
index 8a9d7e2..4bb0433 100644
--- a/_setup_env.sh
+++ b/_setup_env.sh
@@ -131,12 +131,45 @@ if [ "${HERMETIC_TOOLCHAIN:-0}" -eq 1 ]; then
   ldflags+="-L ${ROOT_DIR}/prebuilts/kernel-build-tools/linux-x86/lib64 "
 
   # Have host compiler use LLD and compiler-rt.
-  ldflags+="-fuse-ld=lld --rtlib=compiler-rt"
+  LLD_COMPILER_RT="-fuse-ld=lld --rtlib=compiler-rt"
+  ldflags+=${LLD_COMPILER_RT}
 
   export HOSTCFLAGS="$sysroot_flags $cflags"
   export HOSTLDFLAGS="$sysroot_flags $ldflags"
 
-  export USERCFLAGS="--sysroot=/dev/null"
+  if [[ -n "${NDK_TRIPLE}" ]]; then
+    NDK_DIR=${ROOT_DIR}/prebuilts/ndk-r23
+    if [[ ! -d "${NDK_DIR}" ]]; then
+      # Kleaf/Bazel will checkout the ndk to a different directory than
+      # build.sh.
+      NDK_DIR=${ROOT_DIR}/external/prebuilt_ndk
+      if [[ ! -d "${NDK_DIR}" ]]; then
+        echo "ERROR: NDK_TRIPLE set, but unable to find prebuilts/ndk." 1>&2
+        echo "Did you forget to checkout prebuilts/ndk?" 1>&2
+        exit 1
+      fi
+    fi
+    USERCFLAGS="--target=${NDK_TRIPLE} "
+    USERCFLAGS+="--sysroot=${NDK_DIR}/toolchains/llvm/prebuilt/linux-x86_64/sysroot "
+    # Some kernel headers trigger -Wunused-function for unused static functions
+    # with clang; GCC does not warn about unused static inline functions. The
+    # kernel sets __attribute__((maybe_unused)) on such functions when W=1 is
+    # not set.
+    USERCFLAGS+="-Wno-unused-function "
+    # To help debug these flags, consider commenting back in the following, and
+    # add `echo $@ > /tmp/log.txt` and `2>>/tmp/log.txt` to the invocation of $@
+    # in scripts/cc-can-link.sh.
+    #USERCFLAGS+=" -Wl,--verbose -v"
+    # We need to set -fuse-ld=lld for Android's build env since AOSP LLVM's
+    # clang is not configured to use LLD by default, and BFD has been
+    # intentionally removed. This way CC_CAN_LINK can properly link the test in
+    # scripts/cc-can-link.sh.
+    USERLDFLAGS="${LLD_COMPILER_RT} "
+    USERLDFLAGS+="--target=${NDK_TRIPLE} "
+  else
+    USERCFLAGS="--sysroot=/dev/null"
+  fi
+  export USERCFLAGS USERLDFLAGS
 fi
 
 for prebuilt_bin in "${prebuilts_paths[@]}"; do