Remove hardcoded page size when compiling on android

[zhangxp1998]

Summary

Android bionic is no longer using hardcoded page sizes, so remove the
shortcut code path

[cferris]

We are worried that this might cause some secondary performance issues, going from hard-coded to a memory access. We don't think this will be a problem, but want a little more time to verify.

We also considered that it could be a config parameter to the allocator if we want to keep this as constant lookup without a memory access. But there is a change incoming to the config code.

So once that other change is in, we can look at this again. It shouldn't be too long though, probably by the end of the week.

[zhangxp1998]

Friendly ping : ) Any update on this?

[cferris]

Sorry, I've been trying multiple ways of incorporating the value into the config and none of them work easily. They require changes to just about every file in the tree. I have a back up but that simply uses a #define instead of specialized on SCUDO_ANDROID. I think that might be the best way to go since it's not easy to use a config variable for this particular call.

[enh]

In D151585#4593279, @cferris wrote:

Sorry, I've been trying multiple ways of incorporating the value into the config and none of them work easily. They require changes to just about every file in the tree. I have a back up but that simply uses a #define instead of specialized on SCUDO_ANDROID. I think that might be the best way to go since it's not easy to use a config variable for this particular call.

this:

#if defined(PAGE_SIZE)
  if (SCUDO_ANDROID) return PAGE_SIZE;
#endif

would work well with what's in AOSP atm. (the "page size agnostic" builds don't define PAGE_SIZE.)

[cferris]

I followed enh's suggestion in https://reviews.llvm.org/D158123.

compiler-rt/lib/scudo/standalone/common.h

#endif
   __asm__ __volatile__("" ::: "memory");
 }
 
 // Platform specific functions.
 
 extern uptr PageSizeCached;
 uptr getPageSizeSlow();
 inline uptr getPageSizeCached() {
-  // Bionic uses a hardcoded value.
-  if (SCUDO_ANDROID)
-    return 4096U;
   if (LIKELY(PageSizeCached))
     return PageSizeCached;
   return getPageSizeSlow();
 }
 
 // Returns 0 if the number of CPUs could not be determined.
 u32 getNumberOfCPUs();