[Crash-utility] [PATCH] crash/arm64: Determine vabits_actual value from 'TCR_EL1.T1SZ' value in vmcoreinfo

[Bhupesh Sharma]

I have recently sent a kernel patch upstream to add 'TCR_EL1.T1SZ' to
vmcoreinfo for arm64 (see [0]), instead of VA_BITS_ACTUAL.

'crash' can read the 'TCR_EL1.T1SZ' value from vmcoreinfo
[which indicates the size offset of the memory region addressed by
TTBR1_EL1] and hence can be used for determining the vabits_actual
value.

[0].http://lists.infradead.org/pipermail/kexec/2019-November/023962.html

Cc: Dave Anderson <anderson at redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi at linaro.org>
Cc: Prabhakar Kushwaha <prabhakar.pkin at gmail.com>
Cc: crash-utility at redhat.com
Signed-off-by: Bhupesh Sharma <bhsharma at redhat.com>
---
 arm64.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arm64.c b/arm64.c
index af7147d24e20..083491331985 100644
--- a/arm64.c
+++ b/arm64.c
@@ -3856,8 +3856,17 @@ 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(VA_BITS_ACTUAL)"))) {
-				value = atol(string);
+			if ((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);
+				fprintf(fp,  "vmcoreinfo : vabits_actual: %ld\n", value);
 				free(string);
 				machdep->machspec->VA_BITS_ACTUAL = value;
 				machdep->machspec->VA_BITS = value;
-- 
2.7.4