[scudo] Read ARM feature bits using Fuchsia APIs.

[flowerhack]

Summary

Fuchsia uses zx_system_get_features in lieu of getauxval.

Use this call when checking for CRC32 support.

[cryptoad]

compiler-rt/lib/scudo/scudo_utils.cpp

26 ↗

(On Diff #143362)

I would move this in the arm #if with an else for the rest, so we don't even have to include getauxval.
Adjust the # spacing accordingly.

118 ↗

(On Diff #143362)

Same here, I would move this under the arm #if, as a whole function, and put all the rest in the #else.

119 ↗

(On Diff #143362)

We could probably use u32 here instead for consistency.
To stick with the LLVM standard, please capitalize the variable name (eg: HWCap probably or something like that).
Same for rc under.

[cryptoad]

compiler-rt/lib/scudo/scudo_utils.cpp

25 ↗

(On Diff #143387)

So Fuchsia is not POSIX, that block can go in the #else as well.

106 ↗

(On Diff #143387)

Same here, everything in the #else.

[flowerhack]

compiler-rt/lib/scudo/scudo_utils.cpp

25 ↗

(On Diff #143387)

I actually find the nested preprocessor if/elses a little trickier to read, personally o.o;;;

but, made the changes!

[cryptoad]

Sorry, you were right! The initial version was less complicated.
I'm updating this to fallback to it, with the style changes included.

lib/scudo/scudo_utils.cpp

 //===----------------------------------------------------------------------===//
 
 #include "scudo_utils.h"
 
 #if defined(__x86_64__) || defined(__i386__)
 # include <cpuid.h>
 #elif defined(__arm__) || defined(__aarch64__)
 # include "sanitizer_common/sanitizer_getauxval.h"
-# if SANITIZER_POSIX
+# if SANITIZER_FUCHSIA
+#  include <zircon/syscalls.h>
+#  include <zircon/features.h>
+# elif SANITIZER_POSIX
 #  include "sanitizer_common/sanitizer_posix.h"
 #  include <fcntl.h>
 # endif
 #endif
 
 #include <stdarg.h>
 
 // TODO(kostyak): remove __sanitizer *Printf uses in favor for our own less

 // initialized after the other globals, so we can check its value to know if
 // calling getauxval is safe.
 extern "C" SANITIZER_WEAK_ATTRIBUTE char *__progname;
 INLINE bool areBionicGlobalsInitialized() {
   return !SANITIZER_ANDROID || (&__progname && __progname);
 }
 
 bool hasHardwareCRC32() {
+#if SANITIZER_FUCHSIA
+  u32 HWCap;
+  zx_status_t Status = zx_system_get_features(ZX_FEATURE_KIND_CPU, &HWCap);
+  if (Status != ZX_OK || (HWCap & ZX_ARM64_FEATURE_ISA_CRC32) == 0)
+    return false;
+  return true;
+#else
   if (&getauxval && areBionicGlobalsInitialized())
     return !!(getauxval(AT_HWCAP) & HWCAP_CRC32);
   return hasHardwareCRC32ARMPosix();
+#endif  // SANITIZER_FUCHSIA
 }
 #else
 bool hasHardwareCRC32() { return false; }
 #endif  // defined(__x86_64__) || defined(__i386__)
 
 }  // namespace __scudo