[lldb][test] Unify test infrastructure for checking CPU features (#153914)

This addresses limitations in our testing infrastructure for checking
CPU features. Before this
* `getCPUInfo()` was Linux-only, and the
* `@skipUnlessFeature` decorator was Darwin-only and did not consider
the remote (on device) testing use case.

Introduce `CPUFeature` class as an abstraction to hide the
platform-specific implementations to check for CPU features. Unify local
(on host) and remote (on device) test execution by always going through
`test.run_platform_command()` which uses LLDB's `platform shell <cmd>`
command.

Potential future cleanups: I think `@skipUnlessFeature` decorator could
be used in place of code like this:
```
if not self.isAArch64SME():
    self.skipTest("SME must be present.")
if not self.isAArch64SME2():
    self.skipTest("SME2 must be present.")
```

3 files changed, 103 insertions, 62 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/cpu_feature.py b/lldb/packages/Python/lldbsuite/test/cpu_feature.py
new file mode 100644
index 0000000..3f43cbb
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/cpu_feature.py
@@ -0,0 +1,75 @@
+"""
+Platform-agnostic helper to query for CPU features.
+"""
+
+import re
+
+
+class CPUFeature:
+    def __init__(self, linux_cpu_info_flag: str = None, darwin_sysctl_key: str = None):
+        self.cpu_info_flag = linux_cpu_info_flag
+        self.sysctl_key = darwin_sysctl_key
+
+    def __str__(self):
+        for arch_class in ALL_ARCHS:
+            for feat_var in dir(arch_class):
+                if self == getattr(arch_class, feat_var):
+                    return f"{arch_class.__name__}.{feat_var}"
+        raise AssertionError("unreachable")
+
+    def is_supported(self, triple, cmd_runner):
+        if re.match(".*-.*-linux", triple):
+            err_msg, res = self._is_supported_linux(cmd_runner)
+        elif re.match(".*-apple-.*", triple):
+            err_msg, res = self._is_supported_darwin(cmd_runner)
+        else:
+            err_msg, res = None, False
+
+        if err_msg:
+            print(f"CPU feature check failed: {err_msg}")
+
+        return res
+
+    def _is_supported_linux(self, cmd_runner):
+        if not self.cpu_info_flag:
+            return f"Unspecified cpuinfo flag for {self}", False
+
+        cmd = "cat /proc/cpuinfo"
+        err, retcode, output = cmd_runner(cmd)
+        if err.Fail() or retcode != 0:
+            return output, False
+
+        # FIXME: simple substring match, e.g., test for 'sme' will be true if
+        # 'sme2' or 'smefa64' is present
+        return None, (self.cpu_info_flag in output)
+
+    def _is_supported_darwin(self, cmd_runner):
+        if not self.sysctl_key:
+            return f"Unspecified sysctl key for {self}", False
+
+        cmd = f"sysctl -n {self.sysctl_key}"
+        err, retcode, output = cmd_runner(cmd)
+        if err.Fail() or retcode != 0:
+            return output, False
+
+        return None, (output.strip() == "1")
+
+
+class AArch64:
+    FPMR = CPUFeature("fpmr")
+    GCS = CPUFeature("gcs")
+    MTE = CPUFeature("mte")
+    MTE_STORE_ONLY = CPUFeature("mtestoreonly")
+    PTR_AUTH = CPUFeature("paca", "hw.optional.arm.FEAT_PAuth2")
+    SME = CPUFeature("sme", "hw.optional.arm.FEAT_SME")
+    SME_FA64 = CPUFeature("smefa64")
+    SME2 = CPUFeature("sme2", "hw.optional.arm.FEAT_SME2")
+    SVE = CPUFeature("sve")
+
+
+class Loong:
+    LASX = CPUFeature("lasx")
+    LSX = CPUFeature("lsx")
+
+
+ALL_ARCHS = [AArch64, Loong]
diff --git a/lldb/packages/Python/lldbsuite/test/decorators.py b/lldb/packages/Python/lldbsuite/test/decorators.py
index 16a58cf..454196e 100644
--- a/lldb/packages/Python/lldbsuite/test/decorators.py
+++ b/lldb/packages/Python/lldbsuite/test/decorators.py
@@ -27,6 +27,7 @@ from lldbsuite.support import funcutils
 from lldbsuite.support import temp_file
 from lldbsuite.test import lldbplatform
 from lldbsuite.test import lldbplatformutil
+from lldbsuite.test.cpu_feature import CPUFeature
 
 
 class DecorateMode:
@@ -1131,24 +1132,13 @@ def skipIfLLVMTargetMissing(target):
     return unittest.skipIf(not found, "requires " + target)
 
 
-# Call sysctl on darwin to see if a specified hardware feature is available on this machine.
-def skipUnlessFeature(feature):
-    def is_feature_enabled():
-        if platform.system() == "Darwin":
-            try:
-                output = subprocess.check_output(
-                    ["/usr/sbin/sysctl", feature], stderr=subprocess.DEVNULL
-                ).decode("utf-8")
-                # If 'feature: 1' was output, then this feature is available and
-                # the test should not be skipped.
-                if re.match(r"%s: 1\s*" % feature, output):
-                    return None
-                else:
-                    return "%s is not supported on this system." % feature
-            except subprocess.CalledProcessError:
-                return "%s is not supported on this system." % feature
+def skipUnlessFeature(cpu_feature: CPUFeature):
+    def hasFeature(test_case):
+        if not test_case.isSupported(cpu_feature):
+            return f"Unsupported CPU feature: {cpu_feature}"
+        return None
 
-    return skipTestIfFn(is_feature_enabled)
+    return skipTestIfFn(hasFeature)
 
 
 def skipIfBuildType(types: list[str]):
diff --git a/lldb/packages/Python/lldbsuite/test/lldbtest.py b/lldb/packages/Python/lldbsuite/test/lldbtest.py
index b7077f8..8074922 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbtest.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbtest.py
@@ -48,6 +48,7 @@ import unittest
 # LLDB modules
 import lldb
 from . import configuration
+from . import cpu_feature
 from . import decorators
 from . import lldbplatformutil
 from . import lldbtest_config
@@ -1315,39 +1316,6 @@ class Base(unittest.TestCase):
             return True
         return False
 
-    def getCPUInfo(self):
-        triple = self.dbg.GetSelectedPlatform().GetTriple()
-
-        # TODO other platforms, please implement this function
-        if not re.match(".*-.*-linux", triple):
-            return ""
-
-        # Need to do something different for non-Linux/Android targets
-        cpuinfo_path = self.getBuildArtifact("cpuinfo")
-        if configuration.lldb_platform_name:
-            self.runCmd(
-                'platform get-file "/proc/cpuinfo" ' + cpuinfo_path, check=False
-            )
-            if not self.res.Succeeded():
-                if self.TraceOn():
-                    print(
-                        'Failed to get /proc/cpuinfo from remote: "{}"'.format(
-                            self.res.GetOutput().strip()
-                        )
-                    )
-                    print("All cpuinfo feature checks will fail.")
-                return ""
-        else:
-            cpuinfo_path = "/proc/cpuinfo"
-
-        try:
-            with open(cpuinfo_path, "r") as f:
-                cpuinfo = f.read()
-        except:
-            return ""
-
-        return cpuinfo
-
     def isAArch64(self):
         """Returns true if the architecture is AArch64."""
         arch = self.getArchitecture().lower()
@@ -1360,39 +1328,47 @@ class Base(unittest.TestCase):
             self.getArchitecture().lower().startswith("arm")
         )
 
+    def isSupported(self, cpu_feature: cpu_feature.CPUFeature):
+        triple = self.dbg.GetSelectedPlatform().GetTriple()
+        cmd_runner = self.run_platform_command
+        return cpu_feature.is_supported(triple, cmd_runner)
+
     def isAArch64SVE(self):
-        return self.isAArch64() and "sve" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.SVE)
 
     def isAArch64SME(self):
-        return self.isAArch64() and "sme" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.SME)
 
     def isAArch64SME2(self):
         # If you have sme2, you also have sme.
-        return self.isAArch64() and "sme2" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.SME2)
 
     def isAArch64SMEFA64(self):
         # smefa64 allows the use of the full A64 instruction set in streaming
         # mode. This is required by certain test programs to setup register
         # state.
-        cpuinfo = self.getCPUInfo()
-        return self.isAArch64() and "sme" in cpuinfo and "smefa64" in cpuinfo
+        return (
+            self.isAArch64()
+            and self.isSupported(cpu_feature.AArch64.SME)
+            and self.isSupported(cpu_feature.AArch64.SME_FA64)
+        )
 
     def isAArch64MTE(self):
-        return self.isAArch64() and "mte" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.MTE)
 
     def isAArch64MTEStoreOnly(self):
-        return self.isAArch64() and "mtestoreonly" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.MTE_STORE_ONLY)
 
     def isAArch64GCS(self):
-        return self.isAArch64() and "gcs" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.GCS)
 
     def isAArch64PAuth(self):
         if self.getArchitecture() == "arm64e":
             return True
-        return self.isAArch64() and "paca" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.PTR_AUTH)
 
     def isAArch64FPMR(self):
-        return self.isAArch64() and "fpmr" in self.getCPUInfo()
+        return self.isAArch64() and self.isSupported(cpu_feature.AArch64.FPMR)
 
     def isAArch64Windows(self):
         """Returns true if the architecture is AArch64 and platform windows."""
@@ -1407,10 +1383,10 @@ class Base(unittest.TestCase):
         return arch in ["loongarch64", "loongarch32"]
 
     def isLoongArchLSX(self):
-        return self.isLoongArch() and "lsx" in self.getCPUInfo()
+        return self.isLoongArch() and self.isSupported(cpu_feature.Loong.LSX)
 
     def isLoongArchLASX(self):
-        return self.isLoongArch() and "lasx" in self.getCPUInfo()
+        return self.isLoongArch() and self.isSupported(cpu_feature.Loong.LASX)
 
     def isRISCV(self):
         """Returns true if the architecture is RISCV64 or RISCV32."""