arch: Separately identify arm64_only CPUs without AArch32 support

More and more modern AArch64 SoCs present both in computers and phones
can no longer run normal arm64 image builds which (currently anyway)
also ship various amounts of 32-bit executables that cannot be natively
executed; thus let's target an upcoming arm64_only OTA channel instead.

diff --git a/tools/helpers/arch.py b/tools/helpers/arch.py
index c74ef906574fbc1533e316ecd6e9e7b0c450a9fd..8f4543a582dbd47f9a7e6eaabd12282fbecf54c6 100644 (file)
--- a/tools/helpers/arch.py
+++ b/tools/helpers/arch.py
@@ -2,6 +2,21 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 import platform
 import logging
 # SPDX-License-Identifier: GPL-3.0-or-later
 import platform
 import logging

+import ctypes
+
+def is_32bit_capable():
+    # man 2 personality
+    personality = ctypes.CDLL(None).personality
+    personality.restype = ctypes.c_int
+    personality.argtypes = [ctypes.c_ulong]
+    # linux/include/uapi/linux/personality.h
+    PER_LINUX32 = 0x0008
+    # mirror e.g. https://github.com/util-linux/util-linux/blob/v2.41/sys-utils/lscpu-cputype.c#L745-L756
+    pers = personality(PER_LINUX32)
+    if pers != -1: # success, revert back to previous persona (typically just PER_LINUX, 0x0000)
+        personality(pers)
+        return True
+    return False # unable to "impersonate" 32-bit host, nothing done

 
 def host():
     machine = platform.machine()
 
 def host():
     machine = platform.machine()


@@ -29,5 +44,8 @@ def maybe_remap(target):
             return "x86"
     elif target == "arm64" and platform.architecture()[0] == "32bit":
         return "arm"
             return "x86"
     elif target == "arm64" and platform.architecture()[0] == "32bit":
         return "arm"

+    elif target == "arm64" and not is_32bit_capable():
+        logging.info("AArch64 CPU does not appear to support AArch32, assuming arm64_only...")
+        return "arm64_only"

 
     return target
 
     return target