From 4073aaa7a9df70eeeffbc10fad5a93092e8184a7 Mon Sep 17 00:00:00 2001
From: Tianon Gravi <admwiggin@gmail.com>
Date: Fri, 4 Sep 2020 11:16:47 -0700
Subject: [PATCH] Allow arm64 to fallback to arm (v8, v7, v6, v5)

This isn't supported by *all* arm64 chips, but it is common enough that I think it's worth an explicit fallback.  I think it will be more common for images to have arm64 support without arm support, but even if a user has an arm64 chip that does not support arm32, having it fail to run the arm32 image is an acceptable compromise (because it's non-trivial to detect arm32 support without running a binary, AFAIK).

Also, before this change the failure would've simply been "no such image" instead of "failed to run" so I think it's pretty reasonable to allow it to try the additional 32bit set of images just in case one of them actually does work (like it will on many popular chips like 64bit Raspberry Pis and AWS Graviton).

Signed-off-by: Tianon Gravi <admwiggin@gmail.com>
---
 platforms/compare.go      | 12 ++++++++++++
 platforms/compare_test.go | 10 +++++-----
 platforms/cpuinfo.go      |  7 +------
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/platforms/compare.go b/platforms/compare.go
index af314cbd0..22a86a8a2 100644
--- a/platforms/compare.go
+++ b/platforms/compare.go
@@ -57,6 +57,18 @@ func platformVector(platform specs.Platform) []specs.Platform {
 				})
 			}
 		}
+	case "arm64":
+		variant := platform.Variant
+		if variant == "" {
+			variant = "v8"
+		}
+		vector = append(vector, platformVector(specs.Platform{
+			Architecture: "arm",
+			OS:           platform.OS,
+			OSVersion:    platform.OSVersion,
+			OSFeatures:   platform.OSFeatures,
+			Variant:      variant,
+		})...)
 	}
 
 	return vector
diff --git a/platforms/compare_test.go b/platforms/compare_test.go
index 4e2df5dde..9f6623a81 100644
--- a/platforms/compare_test.go
+++ b/platforms/compare_test.go
@@ -166,17 +166,17 @@ func TestOnly(t *testing.T) {
 			platform: "linux/arm64",
 			matches: map[bool][]string{
 				true: {
+					"linux/arm",
+					"linux/arm/v5",
+					"linux/arm/v6",
+					"linux/arm/v7",
+					"linux/arm/v8",
 					"linux/arm64",
 					"linux/arm64/v8",
 				},
 				false: {
 					"linux/amd64",
-					"linux/arm",
 					"linux/arm/v4",
-					"linux/arm/v5",
-					"linux/arm/v6",
-					"linux/arm/v7",
-					"linux/arm/v8",
 					"linux/arm/v9",
 					"linux/arm64/v9",
 					"windows/amd64",
diff --git a/platforms/cpuinfo.go b/platforms/cpuinfo.go
index 0512bc90e..89c8706a4 100644
--- a/platforms/cpuinfo.go
+++ b/platforms/cpuinfo.go
@@ -107,12 +107,7 @@ func getCPUVariant() string {
 
 	switch strings.ToLower(variant) {
 	case "8", "aarch64":
-		// special case: if running a 32-bit userspace on aarch64, the variant should be "v7"
-		if runtime.GOARCH == "arm" {
-			variant = "v7"
-		} else {
-			variant = "v8"
-		}
+		variant = "v8"
 	case "7", "7m", "?(12)", "?(13)", "?(14)", "?(15)", "?(16)", "?(17)":
 		variant = "v7"
 	case "6", "6tej":