[scudo] getauxval alternative for Android

[cryptoad]

Summary

getauxval was introduced with API level 18. In order to get things to work
at lower API levels (for the toolchain itself which is built at 14 for 32-bit),
we introduce an alternative implementation reading directly from
/proc/self/auxv.

[alekseyshl]

lib/scudo/scudo_utils.cpp

124

Since you are emulating getauxval anyway, wouldn't it be more logical to do just that, define getauxval up there:

// getauxval() was introduced with API level 18 on Android.
# if SANITIZER_ANDROID && __ANDROID_API__ < 18
#  include <fcntl.h>
uptr getauxval(uptr type) {
   ...
}
# else
#  include <sys/auxv.h>
# endif

and then just use it?

uptr HWCap = getauxval(AT_HWCAP);

[alekseyshl]

lib/scudo/scudo_utils.cpp

115

If you agree with redefining getauxval, it should be moved next to the function definition too.

[cryptoad]

Redefining getauxval instead of introducing a third party middleman as
suggested by @alekseyshl.

[cryptoad]

Comment update.

[alekseyshl]

lib/scudo/scudo_utils.cpp

28

It should never be defined here, right? So, we can drop #ifndef.

[cryptoad]

lib/scudo/scudo_utils.cpp

28

True, I was being more conservative than probably needed!

[cryptoad]

Drop the #ifndef AT_HWCAP as it shouldn't be definedi there. If it is,
something is probably wrong somewhere.

[cryptoad]

Adding missing space.

lib/scudo/scudo_utils.cpp

 //===-- scudo_utils.cpp -----------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// Platform specific utility functions.
 ///
 //===----------------------------------------------------------------------===//
 
 #include "scudo_utils.h"
 
-#include <errno.h>
-#include <fcntl.h>
+#include "sanitizer_common/sanitizer_posix.h"
+
 #include <stdarg.h>
-#include <unistd.h>
 #if defined(__x86_64__) || defined(__i386__)
 # include <cpuid.h>
 #endif
 #if defined(__arm__) || defined(__aarch64__)
-# include <sys/auxv.h>
+// getauxval() was introduced with API level 18 on Android.
+# if SANITIZER_ANDROID && __ANDROID_API__ < 18
+#  define SCUDO_USE_GETAUXVAL 0
+# else
+#  define SCUDO_USE_GETAUXVAL 1
+# endif
+# if SCUDO_USE_GETAUXVAL
+#  include <sys/auxv.h>
+# else
+#  include <fcntl.h>
+# endif
 #endif
 
 // 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,
CPUIDRegs getCPUFeatures() {
   // Default to an empty feature set if not on a supported CPU.
   CPUIDRegs FeaturesRegs = {};
   if (IsIntel || IsAMD) {
     getCPUID(&FeaturesRegs, 1);
   }
   return FeaturesRegs;
 }
 
-#ifndef bit_SSE4_2
-# define bit_SSE4_2 bit_SSE42  // clang and gcc have different defines.
-#endif
+# ifndef bit_SSE4_2
+#  define bit_SSE4_2 bit_SSE42  // clang and gcc have different defines.
+# endif
 
 bool testCPUFeature(CPUFeature Feature)
 {
   CPUIDRegs FeaturesRegs = getCPUFeatures();
 
   switch (Feature) {
     case CRC32CPUFeature:  // CRC32 is provided by SSE 4.2.
       return !!(FeaturesRegs.Ecx & bit_SSE4_2);
     default:
       break;
   }
   return false;
 }
 #elif defined(__arm__) || defined(__aarch64__)
-// For ARM and AArch64, hardware CRC32 support is indicated in the
-// AT_HWVAL auxiliary vector.
+// For ARM and AArch64, hardware CRC32 support is indicated in the AT_HWVAL
+// auxiliary vector.
 
-#ifndef HWCAP_CRC32
-# define HWCAP_CRC32 (1<<7)  // HWCAP_CRC32 is missing on older platforms.
-#endif
+# 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 SCUDO_USE_GETAUXVAL
+uptr getHWCap() { return getauxval(AT_HWCAP); }
+# else
+uptr getHWCap() {
+  uptr F = internal_open("/proc/self/auxv", O_RDONLY);
+  if (internal_iserror(F))
+    return 0;
+  struct { uptr Tag; uptr Value; } Entry;
+  uptr Result = 0;
+  for (;;) {
+    uptr N = internal_read(F, &Entry, sizeof(Entry));
+    if (internal_iserror(N))
+      break;
+    if (N == 0 || N != sizeof(Entry) || (Entry.Tag == 0 && Entry.Value == 0))
+      break;
+    if (Entry.Tag == AT_HWCAP) {
+      Result =  Entry.Value;
+      break;
+    }
+  }
+  internal_close(F);
+  return Result;
+}
+# endif  // SCUDO_USE_GETAUXVAL
+
 bool testCPUFeature(CPUFeature Feature) {
-  uptr HWCap = getauxval(AT_HWCAP);
+  uptr HWCap = getHWCap();
 
   switch (Feature) {
     case CRC32CPUFeature:
       return !!(HWCap & HWCAP_CRC32);
     default:
       break;
   }
   return false;
 }
 #else
 bool testCPUFeature(CPUFeature Feature) {
   return false;
 }
 #endif  // defined(__x86_64__) || defined(__i386__)
 
 }  // namespace __scudo