[lldb][AArch64] Simplify MTE memory region test

[DavidSpickett]

Summary

By checking for cpu and toolchain features ahead
of time we don't need the custom return codes.

[DavidSpickett]

Pulling in compiler predicate from https://reviews.llvm.org/D95601
to get this landed before I attempt to fix the race condition
in hasLinuxVmFlags.

[DavidSpickett]

Going to commit this with the compiler predicate since this was accepted already and Omair has reviewed the test predicate in the other review.

lldb/test/API/linux/aarch64/mte_memory_region/TestAArch64LinuxMTEMemoryRegion.py

 
 
 class AArch64LinuxMTEMemoryRegionTestCase(TestBase):
 
     mydir = TestBase.compute_mydir(__file__)
 
     NO_DEBUG_INFO_TESTCASE = True
 
-    @skipIf(archs=no_match(["aarch64"]))
+    @skipUnlessArch("aarch64")
     @skipUnlessPlatform(["linux"])
+    @skipUnlessAArch64MTELinuxCompiler
     def test_mte_regions(self):
+        if not self.isAArch64MTE():
+            self.skipTest('Target must support MTE.')
         if not self.hasLinuxVmFlags():
             self.skipTest('/proc/{pid}/smaps VmFlags must be present')
 
         self.build()
         self.runCmd("file " + self.getBuildArtifact("a.out"), CURRENT_EXECUTABLE_SET)
 
         lldbutil.run_break_set_by_file_and_line(self, "main.c",
             line_number('main.c', '// Set break point at this line.'),
             num_expected_locations=1)
 
         self.runCmd("run", RUN_SUCCEEDED)
 
         if self.process().GetState() == lldb.eStateExited:
-            # 47 = non MTE toolchain
-            # 48 = non MTE target
-            exit_status = self.process().GetExitStatus()
-            if exit_status == 47:
-                self.skipTest("MTE must be available in toolchain")
-            elif exit_status == 48:
-                self.skipTest("target must have MTE enabled")
-
-            # Otherwise we have MTE but another problem occured
             self.fail("Test program failed to run.")
 
         self.expect("thread list", STOPPED_DUE_TO_BREAKPOINT,
             substrs=['stopped',
                      'stop reason = breakpoint'])
 
         substrs = ["memory tagging: enabled"]
         # The new page will be tagged
         self.expect("memory region the_page", substrs=substrs)
         # Code page will not be
         self.expect("memory region main", substrs=substrs, matching=False)

lldb/test/API/linux/aarch64/mte_memory_region/main.c

 #include <asm/hwcap.h>
 #include <asm/mman.h>
 #include <sys/auxv.h>
 #include <sys/mman.h>
 #include <sys/prctl.h>
 #include <unistd.h>
 
-#define INCOMPATIBLE_TOOLCHAIN 47
-#define INCOMPATIBLE_TARGET 48
-
-// This is in a seperate non static function
-// so that we can always breakpoint the return 0 here.
-// Even if main never reaches it because HWCAP2_MTE
-// is not defined.
-// If it were in main then you would effectively have:
-// return TEST_INCOMPATIBLE;
-// return 0;
-// So the two returns would have the same breakpoint location
-// and we couldn't tell them apart.
-int setup_mte_page(void) {
-#ifdef HWCAP2_MTE
+int main(int argc, char const *argv[]) {
   if (!(getauxval(AT_HWCAP2) & HWCAP2_MTE))
-    return INCOMPATIBLE_TARGET;
+    return 1;
 
   int got = prctl(PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE, 0, 0, 0);
   if (got)
     return 1;
 
   void *the_page = mmap(0, sysconf(_SC_PAGESIZE), PROT_MTE,
                         MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   if (the_page == MAP_FAILED)
     return 1;
-#endif
 
   return 0; // Set break point at this line.
 }
-
-int main(int argc, char const *argv[]) {
-#ifdef HWCAP2_MTE
-  return setup_mte_page();
-#else
-  return INCOMPATIBLE_TOOLCHAIN;
-#endif
-}