[Sanitizer] Update macOS version checking

[yln]

Summary

Support macOS 11 in our runtime version checking code and update
GetMacosAlignedVersionInternal() accordingly. This follows the
implementation of Triple::getMacOSXVersion() in the Clang driver.

[yln]

Align implementation with the corresponding change int the
Clang driver (https://reviews.llvm.org/D82337).
We follow the same approach as Triple::getMacOSXVersion().

[delcypher]

Other than minor nit LGTM.

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

612–624

Nit: Could we keep const u16 version_offset = 4 and use?

[yln]

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

612–624

I decided to revert this back to int literals for 2 reasons:

• Make it more similar to Triple::getMacOSXVersion(), so it will be easier to follow any changes made there.
• We now have 2 version offsets: pre and post macOS 11; and I couldn't come up with names that weren't too unwieldy (version_offset_pre_macos_11 = 4) while retaining symmetry (having a named constant for both offsets).

[delcypher]

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

612–624

Make it more similar to Triple::getMacOSXVersion(), so it will be easier to follow any changes made there.

Is this actually a goal? If it is then a commit message and a comment should explicitly call this out, right now the relationship isn't obvious. However, I'm not convinced trying to stylistically mimic Clang's code is the right thing to do.

We now have 2 version offsets: pre and post macOS 11; and I couldn't come up with names that weren't too unwieldy (version_offset_pre_macos_11 = 4) while retaining symmetry (having a named constant for both offsets).

I see. I don't think version_offset_pre_macos_11 is that unwieldy but it's your call.

If you want to land this as is then I'd like you to add a comment to the source and in the commit message explaining the relationship between Triple::getMacOSXVersion() and this code.

[yln]

Add explaining comments.

[delcypher]

LGTM

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

HandleSignalMode GetHandleSignalMode(int signum) {
   if ((SANITIZER_WATCHOS || SANITIZER_TVOS) && !(SANITIZER_IOSSIM))
     return kHandleSignalNo;
   HandleSignalMode result = GetHandleSignalModeImpl(signum);
   if (result == kHandleSignalYes && !common_flags()->allow_user_segv_handler)
     return kHandleSignalExclusive;
   return result;
 }
 
+// This corresponds to Triple::getMacOSXVersion() in the Clang driver.
 static MacosVersion GetMacosAlignedVersionInternal() {
   u16 kernel_major = GetDarwinKernelVersion().major;
-  const u16 version_offset = 4;
-  CHECK_GE(kernel_major, version_offset);
-  u16 macos_major = kernel_major - version_offset;
-  return MacosVersion(10, macos_major);
+  // Darwin 0-3  -> unsupported
+  // Darwin 4-19 -> macOS 10.x
+  // Darwin 20+  -> macOS 11+
+  CHECK_GE(kernel_major, 4);
+  u16 major, minor;
+  if (kernel_major < 20) {
+    major = 10;
+    minor = kernel_major - 4;
+  } else {
+    major = 11 + kernel_major - 20;
+    minor = 0;
+  }
+  return MacosVersion(major, minor);
 }
 
 static_assert(sizeof(MacosVersion) == sizeof(atomic_uint32_t::Type),
               "MacosVersion cache size");
 static atomic_uint32_t cached_macos_version;
 
 MacosVersion GetMacosAlignedVersion() {
   atomic_uint32_t::Type result =

compiler-rt/lib/sanitizer_common/tests/sanitizer_mac_test.cpp

 
 #include <sys/sysctl.h>  // sysctlbyname
 #include <mach/kern_return.h>  // KERN_SUCCESS
 
 namespace __sanitizer {
 
 TEST(SanitizerMac, GetMacosAlignedVersion) {
   MacosVersion vers = GetMacosAlignedVersion();
-  EXPECT_EQ(vers.major, 10);
-  EXPECT_EQ(vers.minor, GetDarwinKernelVersion().major - 4);
+  u16 kernel_major = GetDarwinKernelVersion().major;
+  bool macos_11 = (kernel_major >= 20);
+  u16 expected_major = macos_11 ? (kernel_major - 9) : 10;
+  u16 expected_minor = macos_11 ? 0 : (kernel_major - 4);
+  EXPECT_EQ(vers.major, expected_major);
+  EXPECT_EQ(vers.minor, expected_minor);
 }
 
 void ParseVersion(const char *vers, u16 *major, u16 *minor);
 
 TEST(SanitizerMac, ParseVersion) {
   u16 major, minor;
   ParseVersion("11.22.33", &major, &minor);
   EXPECT_EQ(major, 11);