[PATCH 14/15] riscv: provide a flat image loader

[Christoph Hellwig]

This allows just loading the kernel at a pre-set address without
qemu going bonkers trying to map the ELF file.

Contains a controbution from Aurabindo Jayamohanan to reuse the
PAGE_OFFSET definition.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 arch/riscv/Makefile          | 13 +++++++++----
 arch/riscv/boot/Makefile     |  7 ++++++-
 arch/riscv/boot/loader.S     |  8 ++++++++
 arch/riscv/boot/loader.lds.S | 16 ++++++++++++++++
 4 files changed, 39 insertions(+), 5 deletions(-)
 create mode 100644 arch/riscv/boot/loader.S
 create mode 100644 arch/riscv/boot/loader.lds.S

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index f5e914210245..b9009a2fbaf5 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -83,13 +83,18 @@ PHONY += vdso_install
 vdso_install:
 	$(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@
 
-all: Image.gz
+ifeq ($(CONFIG_RISCV_M_MODE),y)
+KBUILD_IMAGE := $(boot)/loader
+else
+KBUILD_IMAGE := $(boot)/Image.gz
+endif
+BOOT_TARGETS := Image Image.gz loader
 
-Image: vmlinux
-	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+all:	$(notdir $(KBUILD_IMAGE))
 
-Image.%: Image
+$(BOOT_TARGETS): vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+	@$(kecho) '  Kernel: $(boot)/$@ is ready'
 
 zinstall install:
 	$(Q)$(MAKE) $(build)=$(boot) $@
diff --git a/arch/riscv/boot/Makefile b/arch/riscv/boot/Makefile
index 0990a9fdbe5d..8639e0dd2cdf 100644
--- a/arch/riscv/boot/Makefile
+++ b/arch/riscv/boot/Makefile
@@ -16,7 +16,7 @@
 
 OBJCOPYFLAGS_Image :=-O binary -R .note -R .note.gnu.build-id -R .comment -S
 
-targets := Image
+targets := Image loader
 
 $(obj)/Image: vmlinux FORCE
 	$(call if_changed,objcopy)
@@ -24,6 +24,11 @@ $(obj)/Image: vmlinux FORCE
 $(obj)/Image.gz: $(obj)/Image FORCE
 	$(call if_changed,gzip)
 
+loader.o: $(src)/loader.S $(obj)/Image
+
+$(obj)/loader: $(obj)/loader.o $(obj)/Image $(obj)/loader.lds FORCE
+	$(Q)$(LD) -T $(src)/loader.lds -o $@ $(obj)/loader.o
+
 install:
 	$(CONFIG_SHELL) $(srctree)/$(src)/install.sh $(KERNELRELEASE) \
 	$(obj)/Image System.map "$(INSTALL_PATH)"
diff --git a/arch/riscv/boot/loader.S b/arch/riscv/boot/loader.S
new file mode 100644
index 000000000000..5586e2610dbb
--- /dev/null
+++ b/arch/riscv/boot/loader.S
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+	.align 4
+	.section .payload, "ax", %progbits
+	.globl _start
+_start:
+	.incbin "arch/riscv/boot/Image"
+
diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
new file mode 100644
index 000000000000..47a5003c2e28
--- /dev/null
+++ b/arch/riscv/boot/loader.lds.S
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <asm/page.h>
+
+OUTPUT_ARCH(riscv)
+ENTRY(_start)
+
+SECTIONS
+{
+	. = PAGE_OFFSET;
+
+	.payload : {
+		*(.payload)
+		. = ALIGN(8);
+	}
+}
-- 
2.20.1