[PATCH] arm64: deduce the start address of kernel code, based on kernel version

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After kernel commit e2a073dde921 ("arm64: omit [_text, _stext) from
permanent kernel mapping"), the range [_text, _stext] is reclaimed. But
the current crash code still assumes kernel starting from "_text".

This change only affects the vmalloced area on arm64 and may result a
false in arm64_IS_VMALLOC_ADDR().

Since vmcore has no extra information about this trival change, it can
only be deduced from kernel version, which means ms->kimage_text can not
be correctly initialized until kernel_init() finishes. This is fine
since there is no access to vmalloced area at this early stage.

Signed-off-by: Pingfan Liu <piliu@xxxxxxxxxx>
---
 arm64.c  | 17 +++++++++++++++++
 defs.h   |  1 +
 kernel.c |  3 +++
 3 files changed, 21 insertions(+)

diff --git a/arm64.c b/arm64.c
index 4f2c2b5..4aa971c 100644
--- a/arm64.c
+++ b/arm64.c
@@ -92,6 +92,21 @@ static void arm64_calc_VA_BITS(void);
 static int arm64_is_uvaddr(ulong, struct task_context *);
 static void arm64_calc_KERNELPACMASK(void);
 
+/* called by kernel_init() */
+static void arm64_post_kernel_init(void)
+{
+	struct machine_specific *ms = machdep->machspec;
+	struct syment *sp;
+
+	if (THIS_KERNEL_VERSION >= LINUX(5,11,0))
+		sp = kernel_symbol_search("_stext");
+	else
+		sp = kernel_symbol_search("_text");
+
+	ms->kimage_text = (sp ? sp->value : 0);
+	sp = kernel_symbol_search("_end");
+	ms->kimage_end = (sp ? sp->value : 0);
+}
 
 /*
  * Do all necessary machine-specific setup here. This is called several times
@@ -104,6 +119,7 @@ arm64_init(int when)
 	char *string;
 	struct machine_specific *ms;
 
+	arch_post_kernel_init = arm64_post_kernel_init;
 #if defined(__x86_64__)
 	if (ACTIVE())
 		error(FATAL, "compiled for the ARM64 architecture\n");
@@ -241,6 +257,7 @@ arm64_init(int when)
 		if (machdep->flags & NEW_VMEMMAP) {
 			struct syment *sp;
 
+			/* It is finally decided in arm64_post_kernel_init() */
 			sp = kernel_symbol_search("_text");
 			ms->kimage_text = (sp ? sp->value : 0);
 			sp = kernel_symbol_search("_end");
diff --git a/defs.h b/defs.h
index 7d386d2..04ab55a 100644
--- a/defs.h
+++ b/defs.h
@@ -5677,6 +5677,7 @@ struct command_table_entry *crash_cmd_table(void);
 /*
  *  kernel.c 
  */ 
+extern void (*arch_post_kernel_init)(void);
 void kernel_init(void);
 void module_init(void);
 void verify_version(void);
diff --git a/kernel.c b/kernel.c
index 9c4aabf..b64ffac 100644
--- a/kernel.c
+++ b/kernel.c
@@ -98,6 +98,7 @@ static char *vmcoreinfo_read_string(const char *);
 static void check_vmcoreinfo(void);
 static int is_pvops_xen(void);
 
+void (*arch_post_kernel_init)(void);
 
 /*
  *  Gather a few kernel basics.
@@ -823,6 +824,8 @@ kernel_init()
 		source_tree_init();
 
 	kt->flags &= ~PRE_KERNEL_INIT;
+	if (arch_post_kernel_init)
+		arch_post_kernel_init();
 }
 
 /*
-- 
2.31.1

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