efi/riscv: libstub: Split off kernel image relocation for builtin stub

The RISC-V build of the EFI stub is part of the core kernel image, and
therefore accesses section markers directly when it needs to figure out
the size of the various section.

The zboot decompressor does not have access to those symbols, but
doesn't really need that either. So let's move handle_kernel_image()
into a separate file (or rather, move everything else into a separate
file) so that the zboot build does not pull in unused code that links to
symbols that it does not define.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/riscv/include/asm/efi.h

@@ -45,4 +45,6 @@ static inline unsigned long efi_get_kimg_min_align(void)
 void efi_virtmap_load(void);
 void efi_virtmap_unload(void);
 
+unsigned long stext_offset(void);
+
 #endif /* _ASM_EFI_H */

drivers/firmware/efi/libstub/Makefile

@@ -88,7 +88,7 @@ lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o \
 lib-$(CONFIG_ARM)		+= arm32-stub.o
 lib-$(CONFIG_ARM64)		+= arm64-stub.o arm64-entry.o
 lib-$(CONFIG_X86)		+= x86-stub.o
-lib-$(CONFIG_RISCV)		+= riscv-stub.o
+lib-$(CONFIG_RISCV)		+= riscv.o riscv-stub.o
 lib-$(CONFIG_LOONGARCH)		+= loongarch-stub.o
 
 CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)

drivers/firmware/efi/libstub/riscv-stub.c

@@ -4,7 +4,6 @@
  */
 
 #include <linux/efi.h>
-#include <linux/libfdt.h>
 
 #include <asm/efi.h>
 #include <asm/sections.h>
@@ -12,82 +11,16 @@
 
 #include "efistub.h"
 
-typedef void __noreturn (*jump_kernel_func)(unsigned long, unsigned long);
-
-static unsigned long hartid;
-
-static int get_boot_hartid_from_fdt(void)
+unsigned long stext_offset(void)
 {
-	const void *fdt;
-	int chosen_node, len;
-	const void *prop;
-
-	fdt = get_efi_config_table(DEVICE_TREE_GUID);
-	if (!fdt)
-		return -EINVAL;
-
-	chosen_node = fdt_path_offset(fdt, "/chosen");
-	if (chosen_node < 0)
-		return -EINVAL;
-
-	prop = fdt_getprop((void *)fdt, chosen_node, "boot-hartid", &len);
-	if (!prop)
-		return -EINVAL;
-
-	if (len == sizeof(u32))
-		hartid = (unsigned long) fdt32_to_cpu(*(fdt32_t *)prop);
-	else if (len == sizeof(u64))
-		hartid = (unsigned long) fdt64_to_cpu(__get_unaligned_t(fdt64_t, prop));
-	else
-		return -EINVAL;
-
-	return 0;
-}
-
-static efi_status_t get_boot_hartid_from_efi(void)
-{
-	efi_guid_t boot_protocol_guid = RISCV_EFI_BOOT_PROTOCOL_GUID;
-	struct riscv_efi_boot_protocol *boot_protocol;
-	efi_status_t status;
-
-	status = efi_bs_call(locate_protocol, &boot_protocol_guid, NULL,
-			     (void **)&boot_protocol);
-	if (status != EFI_SUCCESS)
-		return status;
-	return efi_call_proto(boot_protocol, get_boot_hartid, &hartid);
-}
-
-efi_status_t check_platform_features(void)
-{
-	efi_status_t status;
-	int ret;
-
-	status = get_boot_hartid_from_efi();
-	if (status != EFI_SUCCESS) {
-		ret = get_boot_hartid_from_fdt();
-		if (ret) {
-			efi_err("Failed to get boot hartid!\n");
-			return EFI_UNSUPPORTED;
-		}
-	}
-	return EFI_SUCCESS;
-}
-
-void __noreturn efi_enter_kernel(unsigned long entrypoint, unsigned long fdt,
-				 unsigned long fdt_size)
-{
-	unsigned long stext_offset = _start_kernel - _start;
-	unsigned long kernel_entry = entrypoint + stext_offset;
-	jump_kernel_func jump_kernel = (jump_kernel_func)kernel_entry;
-
 	/*
-	 * Jump to real kernel here with following constraints.
-	 * 1. MMU should be disabled.
-	 * 2. a0 should contain hartid
-	 * 3. a1 should DT address
+	 * When built as part of the kernel, the EFI stub cannot branch to the
+	 * kernel proper via the image header, as the PE/COFF header is
+	 * strictly not part of the in-memory presentation of the image, only
+	 * of the file representation. So instead, we need to jump to the
+	 * actual entrypoint in the .text region of the image.
 	 */
-	csr_write(CSR_SATP, 0);
-	jump_kernel(hartid, fdt);
+	return _start_kernel - _start;
 }
 
 efi_status_t handle_kernel_image(unsigned long *image_addr,

drivers/firmware/efi/libstub/riscv.c

@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ */
+
+#include <linux/efi.h>
+#include <linux/libfdt.h>
+
+#include <asm/efi.h>
+#include <asm/unaligned.h>
+
+#include "efistub.h"
+
+typedef void __noreturn (*jump_kernel_func)(unsigned long, unsigned long);
+
+static unsigned long hartid;
+
+static int get_boot_hartid_from_fdt(void)
+{
+	const void *fdt;
+	int chosen_node, len;
+	const void *prop;
+
+	fdt = get_efi_config_table(DEVICE_TREE_GUID);
+	if (!fdt)
+		return -EINVAL;
+
+	chosen_node = fdt_path_offset(fdt, "/chosen");
+	if (chosen_node < 0)
+		return -EINVAL;
+
+	prop = fdt_getprop((void *)fdt, chosen_node, "boot-hartid", &len);
+	if (!prop)
+		return -EINVAL;
+
+	if (len == sizeof(u32))
+		hartid = (unsigned long) fdt32_to_cpu(*(fdt32_t *)prop);
+	else if (len == sizeof(u64))
+		hartid = (unsigned long) fdt64_to_cpu(__get_unaligned_t(fdt64_t, prop));
+	else
+		return -EINVAL;
+
+	return 0;
+}
+
+static efi_status_t get_boot_hartid_from_efi(void)
+{
+	efi_guid_t boot_protocol_guid = RISCV_EFI_BOOT_PROTOCOL_GUID;
+	struct riscv_efi_boot_protocol *boot_protocol;
+	efi_status_t status;
+
+	status = efi_bs_call(locate_protocol, &boot_protocol_guid, NULL,
+			     (void **)&boot_protocol);
+	if (status != EFI_SUCCESS)
+		return status;
+	return efi_call_proto(boot_protocol, get_boot_hartid, &hartid);
+}
+
+efi_status_t check_platform_features(void)
+{
+	efi_status_t status;
+	int ret;
+
+	status = get_boot_hartid_from_efi();
+	if (status != EFI_SUCCESS) {
+		ret = get_boot_hartid_from_fdt();
+		if (ret) {
+			efi_err("Failed to get boot hartid!\n");
+			return EFI_UNSUPPORTED;
+		}
+	}
+	return EFI_SUCCESS;
+}
+
+unsigned long __weak stext_offset(void)
+{
+	/*
+	 * This fallback definition is used by the EFI zboot stub, which loads
+	 * the entire image so it can branch via the image header at offset #0.
+	 */
+	return 0;
+}
+
+void __noreturn efi_enter_kernel(unsigned long entrypoint, unsigned long fdt,
+				 unsigned long fdt_size)
+{
+	unsigned long kernel_entry = entrypoint + stext_offset();
+	jump_kernel_func jump_kernel = (jump_kernel_func)kernel_entry;
+
+	/*
+	 * Jump to real kernel here with following constraints.
+	 * 1. MMU should be disabled.
+	 * 2. a0 should contain hartid
+	 * 3. a1 should DT address
+	 */
+	csr_write(CSR_SATP, 0);
+	jump_kernel(hartid, fdt);
+}