RISC-V: Build flat and compressed kernel images

This patch extends Linux RISC-V build system to build and install:
Image - Flat uncompressed kernel image
Image.gz - Flat and GZip compressed kernel image

Quiet a few bootloaders (such as Uboot, UEFI, etc) are capable of
booting flat and compressed kernel images. In case of Uboot, booting
Image or Image.gz is achieved using bootm command.

The flat and uncompressed kernel image (i.e. Image) is very useful
in pre-silicon developent and testing because we can create back-door
HEX files for RAM on FPGAs from Image.
Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/Makefile

@@ -71,6 +71,10 @@ KBUILD_CFLAGS += $(call cc-option,-mstrict-align)
 # arch specific predefines for sparse
 CHECKFLAGS += -D__riscv -D__riscv_xlen=$(BITS)
 
+# Default target when executing plain make
+boot		:= arch/riscv/boot
+KBUILD_IMAGE	:= $(boot)/Image.gz
+
 head-y := arch/riscv/kernel/head.o
 
 core-y += arch/riscv/kernel/ arch/riscv/mm/
@@ -81,4 +85,13 @@ PHONY += vdso_install
 vdso_install:
 	$(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@
 
-all: vmlinux
+all: Image.gz
+
+Image: vmlinux
+	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+
+Image.%: Image
+	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+
+zinstall install:
+	$(Q)$(MAKE) $(build)=$(boot) $@

arch/riscv/boot/.gitignore

+Image
+Image.gz

arch/riscv/boot/Makefile

+#
+# arch/riscv/boot/Makefile
+#
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 2018, Anup Patel.
+# Author: Anup Patel <anup@brainfault.org>
+#
+# Based on the ia64 and arm64 boot/Makefile.
+#
+
+OBJCOPYFLAGS_Image :=-O binary -R .note -R .note.gnu.build-id -R .comment -S
+
+targets := Image
+
+$(obj)/Image: vmlinux FORCE
+	$(call if_changed,objcopy)
+
+$(obj)/Image.gz: $(obj)/Image FORCE
+	$(call if_changed,gzip)
+
+install:
+	$(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
+	$(obj)/Image System.map "$(INSTALL_PATH)"
+
+zinstall:
+	$(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
+	$(obj)/Image.gz System.map "$(INSTALL_PATH)"

arch/riscv/boot/install.sh

+#!/bin/sh
+#
+# arch/riscv/boot/install.sh
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 1995 by Linus Torvalds
+#
+# Adapted from code in arch/i386/boot/Makefile by H. Peter Anvin
+# Adapted from code in arch/i386/boot/install.sh by Russell King
+#
+# "make install" script for the RISC-V Linux port
+#
+# Arguments:
+#   $1 - kernel version
+#   $2 - kernel image file
+#   $3 - kernel map file
+#   $4 - default install path (blank if root directory)
+#
+
+verify () {
+	if [ ! -f "$1" ]; then
+		echo ""                                                   1>&2
+		echo " *** Missing file: $1"                              1>&2
+		echo ' *** You need to run "make" before "make install".' 1>&2
+		echo ""                                                   1>&2
+		exit 1
+	fi
+}
+
+# Make sure the files actually exist
+verify "$2"
+verify "$3"
+
+# User may have a custom install script
+if [ -x ~/bin/${INSTALLKERNEL} ]; then exec ~/bin/${INSTALLKERNEL} "$@"; fi
+if [ -x /sbin/${INSTALLKERNEL} ]; then exec /sbin/${INSTALLKERNEL} "$@"; fi
+
+if [ "$(basename $2)" = "Image.gz" ]; then
+# Compressed install
+  echo "Installing compressed kernel"
+  base=vmlinuz
+else
+# Normal install
+  echo "Installing normal kernel"
+  base=vmlinux
+fi
+
+if [ -f $4/$base-$1 ]; then
+  mv $4/$base-$1 $4/$base-$1.old
+fi
+cat $2 > $4/$base-$1
+
+# Install system map file
+if [ -f $4/System.map-$1 ]; then
+  mv $4/System.map-$1 $4/System.map-$1.old
+fi
+cp $3 $4/System.map-$1

arch/riscv/kernel/head.S

@@ -44,6 +44,16 @@ ENTRY(_start)
 	amoadd.w a3, a2, (a3)
 	bnez a3, .Lsecondary_start
 
+	/* Clear BSS for flat non-ELF images */
+	la a3, __bss_start
+	la a4, __bss_stop
+	ble a4, a3, clear_bss_done
+clear_bss:
+	REG_S zero, (a3)
+	add a3, a3, RISCV_SZPTR
+	blt a3, a4, clear_bss
+clear_bss_done:
+
 	/* Save hart ID and DTB physical address */
 	mv s0, a0
 	mv s1, a1

arch/riscv/kernel/vmlinux.lds.S

@@ -74,7 +74,7 @@ SECTIONS
 		*(.sbss*)
 	}
 
-	BSS_SECTION(0, 0, 0)
+	BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
 
 	EXCEPTION_TABLE(0x10)
 	NOTES