kernel: update build-kernel.sh script for x86

This updates the build-kernel.sh script to be able to rebuild
the x86 goldfish kernel from sources using our NDK-compatible
toolchain. This is needed because the toolchain is configured
with -mfpmath=sse and -fpic by default, which we need to disable.

Because the kernel build system doesn't allow us to provide extra
compiler flags easily, we create a "magic" wrapper toolchain to
do it for us (see toolbox.sh)

Change-Id: Ie868497dc5543d1149c51f354daa567863b638dc

1 files changed, 52 insertions, 0 deletions

diff --git a/distrib/kernel-toolchain/toolbox.sh b/distrib/kernel-toolchain/toolbox.sh
new file mode 100755
index 0000000..94e89b2
--- /dev/null
+++ b/distrib/kernel-toolchain/toolbox.sh
@@ -0,0 +1,52 @@
+#!/bin/sh
+#
+# This is a wrapper around our x86 toolchain that allows us to add a few
+# compiler flags.
+# The issue is that our x86 toolchain is NDK-compatible, and hence enforces
+# -mfpmath=sse and -fpic by default. When building the kernel, we need to
+# disable this.
+#
+# Also support ccache compilation if USE_CCACHE is defined as "1"
+#
+
+# REAL_CROSS_COMPILE must be defined, and its value must be one of the
+# CROSS_COMPILE values that are supported by the Kernel build system
+# (e.g. "i686-android-linux-")
+#
+if [ -z "$REAL_CROSS_COMPILE" ]; then
+    echo "ERROR: The REAL_CROSS_COMPILE environment variable should be defined!"
+    exit 1
+fi
+
+# ARCH must also be defined before calling this script, e.g. 'arm' or 'x86'
+#
+if [ -z "$ARCH" ]; then
+    echo "ERROR: ARCH must be defined!"
+    exit 1
+fi
+
+# Common prefix for all fake toolchain programs, which are all really
+# symlinks to this script, i.e.
+#
+# $PROGPREFIX-gcc  --> $0
+# $PROGPREFIX-ld   --> $0
+# etc...
+#
+PROGPREFIX=android-kernel-toolchain-
+
+# Get program name, must be of the form $PROGPREFIX-<suffix>, where
+# <suffix> can be 'gcc', 'ld', etc... We expect that the fake toolchain
+# files are all symlinks to this script.
+#
+PROGNAME=$(basename "$0")
+PROGSUFFIX=${PROGNAME##$PROGPREFIX}
+
+EXTRA_FLAGS=
+
+# Special case #1: For x86, disable SSE FPU arithmetic, and PIC code
+if [ "$ARCH" = "x86" -a "$PROGSUFFIX" = gcc ]; then
+    EXTRA_FLAGS=$EXTRA_FLAGS" -mfpmath=387 -fno-pic"
+fi
+
+# Invoke real cross-compiler toolchain program now
+${REAL_CROSS_COMPILE}$PROGSUFFIX $EXTRA_FLAGS "$@"