[scudo] Allow for compile-time choice of the SizeClassMap

[cryptoad]

Summary

With this change, we allow someone to chose the SizeClassMap they want to use
at compile time via a define.

I feel somewhat unimaginative with the name of the defines, so if someone has a
better idea, let me know. I have been alternating between those and
SCUDO_USE_xxx_SIZECLASSMAP which is clearer but also longer. The issue with
those is that it wouldn't be consistent with SCUDO_TSD_EXCLUSIVE that should
probably become SCUDO_USE_EXCLUSIVE_TSD maybe?

Anyway, naming is hard, and I am not sure what makes more sense!

[alekseyshl]

What's wrong with SCUDO_SCM_{DEFAULT|COMPACT|VERY_COMPACT}? If someone wants to tinker with it, they probably aware what SCM stands for and what it affects.

lib/scudo/scudo_platform.h

67

Why not just fold it into #else?

[cryptoad]

lib/scudo/scudo_platform.h

67

Well the train of thought was that the actual default might be different in the future so I wanted to have a separate #else there.

[cryptoad]

I guess another question that I had for you @alekseyshl : would you rather see #if or #ifdef?
I am not sure SCUDO_SCM_DEFAULT=1 makes sense as opposed to it just being defined.

[alekseyshl]

In D40521#937952, @cryptoad wrote:

I guess another question that I had for you @alekseyshl : would you rather see #if or #ifdef?
I am not sure SCUDO_SCM_DEFAULT=1 makes sense as opposed to it just being defined.

Another idea, how about defining the type name?

SCUDO_SIZE_CLASS_MAP={Default|Compact|VeryCompact}

and then do something like this:

#if !defined(SCUDO_SIZE_CLASS_MAP)
# define SCUDO_SIZE_CLASS_MAP Default
#endif

#define SIZE_CLASS_MAP_TYPE SIZE_CLASS_MAP_TYPE_(SCUDO_SIZE_CLASS_MAP)
#define SIZE_CLASS_MAP_TYPE_(T) SIZE_CLASS_MAP_TYPE__(T)
#define SIZE_CLASS_MAP_TYPE__(T) T##SizeClassMap

typedef SIZE_CLASS_MAP_TYPE SizeClassMap;

lib/scudo/scudo_platform.h

67

Default value might be different from the one Scudo defaults to in case it was not defined? Hmm...

[cryptoad]

As per Aleksey's excellent suggestion, allow for the typename to be defined via
SCUDO_SIZE_CLASS_MAP={Default|Compact|VeryCompact}. Which makes a lot more
sense.

lib/scudo/scudo_platform.h

 #ifndef SCUDO_SHARED_TSD_POOL_SIZE
 # define SCUDO_SHARED_TSD_POOL_SIZE 32U
 #endif  // SCUDO_SHARED_TSD_POOL_SIZE
 
 namespace __scudo {
 
 #if SANITIZER_CAN_USE_ALLOCATOR64
 # if defined(__aarch64__) && SANITIZER_ANDROID
-const uptr AllocatorSize = 0x2000000000ULL;  // 128G.
-typedef VeryCompactSizeClassMap SizeClassMap;
+const uptr AllocatorSize = 0x4000000000ULL;  // 256G.
 # elif defined(__aarch64__)
 const uptr AllocatorSize = 0x10000000000ULL;  // 1T.
-typedef CompactSizeClassMap SizeClassMap;
 # else
 const uptr AllocatorSize = 0x40000000000ULL;  // 4T.
-typedef CompactSizeClassMap SizeClassMap;
 # endif
 #else
-# if SANITIZER_ANDROID
-static const uptr RegionSizeLog = 19;
+const uptr RegionSizeLog = SANITIZER_ANDROID ? 19 : 20;
+#endif  // SANITIZER_CAN_USE_ALLOCATOR64
+
+#if SCUDO_SCM_VERYCOMPACT
 typedef VeryCompactSizeClassMap SizeClassMap;
-# else
-static const uptr RegionSizeLog = 20;
+#elif SCUDO_SCM_COMPACT
 typedef CompactSizeClassMap SizeClassMap;
-# endif
-#endif  // SANITIZER_CAN_USE_ALLOCATOR64
+#elif SCUDO_SCM_DEFAULT
+typedef DefaultSizeClassMap SizeClassMap;
+#else
+typedef DefaultSizeClassMap SizeClassMap;
+#endif
 
 }  // namespace __scudo
 
 #endif // SCUDO_PLATFORM_H_