[fuzzer] Don't hard-code page size in FuzzerUtil.h

[Ami-zhang]

Summary

Don't hard code the page in FuzzerUtil.h, this breaks on
e.g. LoongArch which defaults to a 16KiB page size.

[vitalybuka]

After revert we reopen previous review

[Ami-zhang]

In D151530#4374970, @vitalybuka wrote:

After revert we reopen previous review

Ok, thanks.
I have resubmitted on D140607.
Abandon this change.

compiler-rt/lib/fuzzer/FuzzerUtil.h

 std::string SearchRegexCmd(const std::string &Regex);
 
 uint64_t SimpleFastHash(const void *Data, size_t Size, uint64_t Initial = 0);
 
 inline size_t Log(size_t X) {
   return static_cast<size_t>((sizeof(unsigned long long) * 8) - Clzll(X) - 1);
 }
 
-inline size_t PageSize() { return 4096; }
+size_t PageSize();
+
 inline uint8_t *RoundUpByPage(uint8_t *P) {
   uintptr_t X = reinterpret_cast<uintptr_t>(P);
   size_t Mask = PageSize() - 1;
   X = (X + Mask) & ~Mask;
   return reinterpret_cast<uint8_t *>(X);
 }
 inline uint8_t *RoundDownByPage(uint8_t *P) {
   uintptr_t X = reinterpret_cast<uintptr_t>(P);

compiler-rt/lib/fuzzer/FuzzerUtil.cpp

 #include <cstring>
 #include <errno.h>
 #include <mutex>
 #include <signal.h>
 #include <sstream>
 #include <stdio.h>
 #include <sys/types.h>
 #include <thread>
+#include <unistd.h>
 
 namespace fuzzer {
 
 void PrintHexArray(const uint8_t *Data, size_t Size,
                    const char *PrintAfter) {
   for (size_t i = 0; i < Size; i++)
     Printf("0x%x,", (unsigned)Data[i]);
   Printf("%s", PrintAfter);

 uint64_t SimpleFastHash(const void *Data, size_t Size, uint64_t Initial) {
   uint64_t Res = Initial;
   const uint8_t *Bytes = static_cast<const uint8_t *>(Data);
   for (size_t i = 0; i < Size; i++)
     Res = Res * 11 + Bytes[i];
   return Res;
 }
 
+size_t PageSize() {
+  static size_t PageSizeCached = sysconf(_SC_PAGESIZE);
+  return PageSizeCached;
+}
+
 }  // namespace fuzzer