crash: remove dependency of FA_DUMP on CRASH_DUMP

In kdump kernel, /proc/vmcore is an elf file mapping the crashed kernel's
old memory content. Its elf header is constructed in 1st kernel and passed
to kdump kernel via elfcorehdr_addr. Config CRASH_DUMP enables the code
of 1st kernel's old memory accessing in different architectures.

Currently, config FA_DUMP has dependency on CRASH_DUMP because fadump
needs access global variable 'elfcorehdr_addr' to judge if it's in
kdump kernel within function is_kdump_kernel(). In the current
kernel/crash_dump.c, variable 'elfcorehdr_addr' is defined, and function
setup_elfcorehdr() used to parse kernel parameter to fetch the passed
value of elfcorehdr_addr. Only for accessing elfcorehdr_addr, FA_DUMP
really doesn't have to depends on CRASH_DUMP.

To remove the dependency of FA_DUMP on CRASH_DUMP to avoid confusion,
rename kernel/crash_dump.c to kernel/elfcorehdr.c, and build it when
CONFIG_VMCORE_INFO is ebabled. With this, FA_DUMP doesn't need to depend
on CRASH_DUMP.

[bhe@redhat.com: power/fadump: make FA_DUMP select CRASH_DUMP]
  Link: https://lkml.kernel.org/r/Zb8D1ASrgX0qVm9z@MiWiFi-R3L-srv
Link: https://lkml.kernel.org/r/20240124051254.67105-4-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Pingfan Liu <piliu@redhat.com>
Cc: Klara Modin <klarasmodin@gmail.com>
Cc: Michael Kelley <mhklinux@outlook.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 41 insertions, 0 deletions

diff --git a/kernel/elfcorehdr.c b/kernel/elfcorehdr.c
new file mode 100644
index 000000000000..92da32275af5
--- /dev/null
+++ b/kernel/elfcorehdr.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/crash_dump.h>
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/export.h>
+
+/*
+ * stores the physical address of elf header of crash image
+ *
+ * Note: elfcorehdr_addr is not just limited to vmcore. It is also used by
+ * is_kdump_kernel() to determine if we are booting after a panic. Hence put
+ * it under CONFIG_CRASH_DUMP and not CONFIG_PROC_VMCORE.
+ */
+unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
+EXPORT_SYMBOL_GPL(elfcorehdr_addr);
+
+/*
+ * stores the size of elf header of crash image
+ */
+unsigned long long elfcorehdr_size;
+
+/*
+ * elfcorehdr= specifies the location of elf core header stored by the crashed
+ * kernel. This option will be passed by kexec loader to the capture kernel.
+ *
+ * Syntax: elfcorehdr=[size[KMG]@]offset[KMG]
+ */
+static int __init setup_elfcorehdr(char *arg)
+{
+	char *end;
+	if (!arg)
+		return -EINVAL;
+	elfcorehdr_addr = memparse(arg, &end);
+	if (*end == '@') {
+		elfcorehdr_size = elfcorehdr_addr;
+		elfcorehdr_addr = memparse(end + 1, &end);
+	}
+	return end > arg ? 0 : -EINVAL;
+}
+early_param("elfcorehdr", setup_elfcorehdr);