[Crash-utility] [PATCH] arm64: use TCR_EL1_T1SZ to get the correct info if vabits_actual is missing

[Huang Shijie]

After kernel patch:
   "0d9b1ffefabe arm64: mm: make vabits_actual a build time constant if possible"
the "vabits_actual" is not compiled to kernel symbols when "VA_BITS > 48"
is false.

So the crash will not find the "vabits_actual" symbol, and it will
fail in the end.

This patch introduces the arm64_set_va_bits_by_tcr(), and if crash cannot
find "vabits_actual" symbol, it will use the TCR_EL1_T1SZ register to get
the correct VA_BITS_ACTUAL/VA_BITS/VA_START.

Tested this patch with:
	1.) the live mode with /proc/kcore
	2.) the kdump file with /proc/vmcore.

Signed-off-by: Huang Shijie <shijie at os.amperecomputing.com>
---
 arm64.c | 50 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 33 insertions(+), 17 deletions(-)

diff --git a/arm64.c b/arm64.c
index b6b7aa1..3a613f9 100644
--- a/arm64.c
+++ b/arm64.c
@@ -4586,6 +4586,35 @@ arm64_IS_VMALLOC_ADDR(ulong vaddr)
                 (vaddr >= ms->modules_vaddr && vaddr <= ms->modules_end));
 }
 
+/* Return TRUE if we succeed, return FALSE on failure. */
+static int arm64_set_va_bits_by_tcr()
+{
+	ulong value;
+	char *string;
+
+	if ((string = pc->read_vmcoreinfo("NUMBER(TCR_EL1_T1SZ)")) ||
+	    (string = pc->read_vmcoreinfo("NUMBER(tcr_el1_t1sz)"))) {
+		/* See ARMv8 ARM for the description of
+		 * TCR_EL1.T1SZ and how it can be used
+		 * to calculate the vabits_actual
+		 * supported by underlying kernel.
+		 *
+		 * Basically:
+		 * vabits_actual = 64 - T1SZ;
+		 */
+		value = 64 - strtoll(string, NULL, 0);
+		if (CRASHDEBUG(1))
+			fprintf(fp,  "vmcoreinfo : vabits_actual: %ld\n", value);
+		free(string);
+		machdep->machspec->VA_BITS_ACTUAL = value;
+		machdep->machspec->VA_BITS = value;
+		machdep->machspec->VA_START = _VA_START(machdep->machspec->VA_BITS_ACTUAL);
+		return TRUE;
+	}
+
+	return FALSE;
+}
+
 static void 
 arm64_calc_VA_BITS(void)
 {
@@ -4616,23 +4645,8 @@ arm64_calc_VA_BITS(void)
 		} else if (ACTIVE())
 			error(FATAL, "cannot determine VA_BITS_ACTUAL: please use /proc/kcore\n");
 		else {
-			if ((string = pc->read_vmcoreinfo("NUMBER(TCR_EL1_T1SZ)")) ||
-			    (string = pc->read_vmcoreinfo("NUMBER(tcr_el1_t1sz)"))) {
-				/* See ARMv8 ARM for the description of
-				 * TCR_EL1.T1SZ and how it can be used
-				 * to calculate the vabits_actual
-				 * supported by underlying kernel.
-				 *
-				 * Basically:
-				 * vabits_actual = 64 - T1SZ;
-				 */
-				value = 64 - strtoll(string, NULL, 0);
-				if (CRASHDEBUG(1))
-					fprintf(fp,  "vmcoreinfo : vabits_actual: %ld\n", value);
-				free(string);
-				machdep->machspec->VA_BITS_ACTUAL = value;
-				machdep->machspec->VA_BITS = value;
-				machdep->machspec->VA_START = _VA_START(machdep->machspec->VA_BITS_ACTUAL);
+			if (arm64_set_va_bits_by_tcr()) {
+				/* nothing */
 			} else if (machdep->machspec->VA_BITS_ACTUAL) {
 				machdep->machspec->VA_BITS = machdep->machspec->VA_BITS_ACTUAL;
 				machdep->machspec->VA_START = _VA_START(machdep->machspec->VA_BITS_ACTUAL);
@@ -4654,6 +4668,8 @@ arm64_calc_VA_BITS(void)
 		 */
 		machdep->flags |= FLIPPED_VM;
 		return;
+	} else if (arm64_set_va_bits_by_tcr()) {
+		return;
 	}
 
 	if (!(sp = symbol_search("swapper_pg_dir")) &&
-- 
2.30.2