arm64: kernel: arch_crash_save_vmcoreinfo() should depend on CONFIG_CRASH_CORE

Since commit 23c85094fe18 ("proc/kcore: add vmcoreinfo note to /proc/kcore")
the kernel has exported the vmcoreinfo PT_NOTE on /proc/kcore as well
as /proc/vmcore.

arm64 only exposes it's additional arch information via
arch_crash_save_vmcoreinfo() if built with CONFIG_KEXEC, as kdump was
previously the only user of vmcoreinfo.

Move this weak function to a separate file that is built at the same
time as its caller in kernel/crash_core.c. This ensures values like
'kimage_voffset' are always present in the vmcoreinfo PT_NOTE.

CC: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/Makefile

@@ -54,6 +54,7 @@ arm64-obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o	\
 arm64-obj-$(CONFIG_ARM64_RELOC_TEST)	+= arm64-reloc-test.o
 arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
 arm64-obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.o
+arm64-obj-$(CONFIG_CRASH_CORE)		+= crash_core.o
 arm64-obj-$(CONFIG_ARM_SDE_INTERFACE)	+= sdei.o
 arm64-obj-$(CONFIG_ARM64_SSBD)		+= ssbd.o
 

arch/arm64/kernel/crash_core.c

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Linaro.
+ * Copyright (C) Huawei Futurewei Technologies.
+ */
+
+#include <linux/crash_core.h>
+#include <asm/memory.h>
+
+void arch_crash_save_vmcoreinfo(void)
+{
+	VMCOREINFO_NUMBER(VA_BITS);
+	/* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */
+	vmcoreinfo_append_str("NUMBER(kimage_voffset)=0x%llx\n",
+						kimage_voffset);
+	vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n",
+						PHYS_OFFSET);
+	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
+}

arch/arm64/kernel/machine_kexec.c

@@ -358,14 +358,3 @@ void crash_free_reserved_phys_range(unsigned long begin, unsigned long end)
 	}
 }
 #endif /* CONFIG_HIBERNATION */
-
-void arch_crash_save_vmcoreinfo(void)
-{
-	VMCOREINFO_NUMBER(VA_BITS);
-	/* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */
-	vmcoreinfo_append_str("NUMBER(kimage_voffset)=0x%llx\n",
-						kimage_voffset);
-	vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n",
-						PHYS_OFFSET);
-	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
-}