[lldb][AArch64] Don't check for VmFlags in smaps files

[DavidSpickett]

Summary

AArch64 kernel builds default to having /smaps and
the "VmFlags" line was added in 3.8. Long before MTE
was supported.

So we can assume that if you're AArch64 with MTE,
you can run this test.

The previous method of checking had a race condition
where the process we read smaps for, could finish before
we get to read the file.

I explored some alternatives but in the end I think
it's fine to just assume we have what we need.

[DavidSpickett]

This fixes the underlying issue for the random failure of this test on the lldb bots.

The only way we get bitten here is if someone runs this on a system with smaps disabled but given that that removes your ability to actually debug MTE I don't see it happening.

[DavidSpickett]

lldb/packages/Python/lldbsuite/test/lldbtest.py

1314

When running on a buildbot via lit, this lldb-server could be one of hundreds of test instances. We get unlucky, the test finishes before we can read the file, and this fails.

[DavidSpickett]

Looks like buildkite had issues calling back to Phab yesterday so the builds didn't signal here. This test wouldn't get run in those anyway.

[DavidSpickett]

@omjavaid ping

[omjavaid]

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

42

I think this is LGTM as it is but if you want to add further reliability then may be set a unique executable name so that you can detect only its PID and then read smaps file. You can skip this test at this stage if target doesnt have smaps.

[DavidSpickett]

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

42

That's clever, I didn't think of that. I might do that in a follow up.

lldb/packages/Python/lldbsuite/test/lldbtest.py

def isAArch64SVE(self):
         return "sve" in self.getCPUInfo()
 
     def isAArch64MTE(self):
         return "mte" in self.getCPUInfo()
 
     def isAArch64PAuth(self):
         return "paca" in self.getCPUInfo()
 
-    def hasLinuxVmFlags(self):
-        """ Check that the target machine has "VmFlags" lines in
-        its /proc/{pid}/smaps files."""
-
-        triple = self.dbg.GetSelectedPlatform().GetTriple()
-        if not re.match(".*-.*-linux", triple):
-            return False
-
-        self.runCmd('platform process list')
-        pid = None
-        for line in self.res.GetOutput().splitlines():
-            if 'lldb-server' in line:
-                pid = line.split(' ')[0]
-                break
-
-        if pid is None:
-            return False
-
-        smaps_path = self.getBuildArtifact('smaps')
-        self.runCmd('platform get-file "/proc/{}/smaps" {}'.format(pid, smaps_path))
-
-        with open(smaps_path, 'r') as f:
-            return "VmFlags" in f.read()
-
     def getArchitecture(self):
         """Returns the architecture in effect the test suite is running with."""
         module = builder_module()
         arch = module.getArchitecture()
         if arch == 'amd64':
             arch = 'x86_64'
         if arch in ['armv7l', 'armv8l'] :
             arch = 'arm'

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

class AArch64LinuxMTEMemoryRegionTestCase(TestBase):
     NO_DEBUG_INFO_TESTCASE = True
 
     @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')
+
+        # This test assumes that we have /proc/<PID>/smaps files
+        # that include "VmFlags:" lines.
+        # AArch64 kernel config defaults to enabling smaps with
+        # PROC_PAGE_MONITOR and "VmFlags" was added in kernel 3.8,
+        # before MTE was supported at all.
 
         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:
             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)