[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

32

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.

133

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

134

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

19

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

89

Same here, everything in the #else.

[flowerhack]

compiler-rt/lib/scudo/scudo_utils.cpp

19

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.

compiler-rt/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
 #  include "sanitizer_common/sanitizer_posix.h"
 #  include <fcntl.h>
-# endif
+# else
+#  if SANITIZER_FUCHSIA
+#   include <zircon/syscalls.h>
+#   include <zircon/features.h>
+#  else
+#   include "sanitizer_common/sanitizer_getauxval.h"
+#  endif  //SANITIZER_FUCHSIA
+# endif  // SANITIZER_POSIX
 #endif
 
 #include <stdarg.h>
 
 // TODO(kostyak): remove __sanitizer *Printf uses in favor for our own less
 //                complicated string formatting code. The following is a
 //                temporary workaround to be able to use __sanitizer::VSNPrintf.
 namespace __sanitizer {
 
 extern int VSNPrintf(char *buff, int buff_length, const char *format,
                      va_list args);

 // For ARM and AArch64, hardware CRC32 support is indicated in the AT_HWCAP
 // auxiliary vector.
 # ifndef AT_HWCAP
 #  define AT_HWCAP 16
 # endif
 # ifndef HWCAP_CRC32
 #  define HWCAP_CRC32 (1 << 7)  // HWCAP_CRC32 is missing on older platforms.
 # endif
 # if SANITIZER_POSIX
 bool hasHardwareCRC32ARMPosix() {
   uptr F = internal_open("/proc/self/auxv", O_RDONLY);
   if (internal_iserror(F))
     return false;
   struct { uptr Tag; uptr Value; } Entry = { 0, 0 };
   for (;;) {
     uptr N = internal_read(F, &Entry, sizeof(Entry));
     if (internal_iserror(N) || N != sizeof(Entry) ||
         (Entry.Tag == 0 && Entry.Value == 0) || Entry.Tag == AT_HWCAP)
       break;
   }
   internal_close(F);
   return (Entry.Tag == AT_HWCAP && (Entry.Value & HWCAP_CRC32) != 0);
 }
 # else
 bool hasHardwareCRC32ARMPosix() { return false; }
+#  if SANITIZER_FUCHSIA
+bool hasHardwareCRC32() {
+  u32 HWCap;
+  zx_status_t RetVal = zx_system_get_features(ZX_FEATURE_KIND_CPU, &HWCap);
+  if (RetVal != ZX_OK || (HWCap & ZX_ARM64_FEATURE_ISA_CRC32) == 0) {
+    return false;
+  }
+  return true;
+}
+#  else
+bool hasHardwareCRC32() {
+  if (&getauxval && areBionicGlobalsInitialized())
+    return !!(getauxval(AT_HWCAP) & HWCAP_CRC32);
+  return hasHardwareCRC32ARMPosix();
+}
+#  endif  //SANITIZER_FUCHSIA
 # endif  // SANITIZER_POSIX
 
 // Bionic doesn't initialize its globals early enough. This causes issues when
 // trying to access them from a preinit_array (b/25751302) or from another
 // constructor called before the libc one (b/68046352). __progname is
 // 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 (&getauxval && areBionicGlobalsInitialized())
-    return !!(getauxval(AT_HWCAP) & HWCAP_CRC32);
-  return hasHardwareCRC32ARMPosix();
-}
 #else
 bool hasHardwareCRC32() { return false; }
 #endif  // defined(__x86_64__) || defined(__i386__)
 
 }  // namespace __scudo