lib: detect ARM64 32-bit compat mode as 64-bit kernel

ARM64 (aarch64) identifies itself in 32-bit compatibility mode as armv8l or armv8b depending on endianness. Detect these modes as a 64-bit kernel.

This fixes the following issues on ARM64:
- mmapstress03 segfaults in 32-bit compat mode due to a larger than expected address space
- cve-2016-4997 which was a vulnerability in a 32-bit compat syscall, but the test does not correctly identify 32-bit compat and wouldn't run
- vma03 which only runs on 32-bit arches, it would incorrectly be run on arm64 32-bit mode and fail

Signed-off-by Steve Muckle <[email protected]>

---
Tested on armv8l, aarch64, x86-64 and x86-64 32-bit compat.

  lib/tst_kernel.c | 7 +++++++
  1 file changed, 7 insertions(+)

lib/tst_kernel.c +7 -0

index 71303fc36..fd648b1f2 100644
@@ -31,6 +31,13 @@ int tst_kernel_bits(void)
 
  	kernel_bits = strstr(buf.machine, "64") ? 64 : 32;
 
+	/*
+	 * ARM64 (aarch64) defines 32-bit compatibility modes as
+	 * armv8l and armv8b (little and big endian).
+	 */
+	if (!strcmp(buf.machine, "armv8l") || !strcmp(buf.machine, "armv8b"))
+		kernel_bits = 64;
+
  	tst_resm(TINFO, "uname.machine=%s kernel is %ibit",
  	         buf.machine, kernel_bits);