[sanitizer] Use MADV_FREE on Darwin/BSD to release pages to the OS

[kubamracek]

Summary

MADV_DONTNEED on Linux actually mark the pages as free to be overwritten with zeroes, but on Darwin and BSD, it's just an advisory flag (the OS cannot discard the content). We should use MADV_FREE on Darwin and BSD.

[krytarowski]

lib/sanitizer_common/sanitizer_posix_libcdep.cc

65 ↗

(On Diff #124986)

Please include SANITIZER_NETBSD too (and in the description).

[kcc]

Will this even build on Linux?
I don't see MADV_FREE in /usr/include

Maybe define SANITIZER_MADVISE_DONTNEED in lib/sanitizer_common/sanitizer_platform.h?

[kcc]

LGTM.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform.h

 // dlopen mallocs "libgcc_s.so" string which confuses LSan, it fails to realize
 // that this allocation happens in dynamic linker and should be ignored.
 #if SANITIZER_PPC || defined(__thumb__)
 # define SANITIZER_SUPPRESS_LEAK_ON_PTHREAD_EXIT 1
 #else
 # define SANITIZER_SUPPRESS_LEAK_ON_PTHREAD_EXIT 0
 #endif
 
+#if SANITIZER_FREEBSD || SANITIZER_MAC || SANITIZER_NETBSD
+# define SANITIZER_MADVISE_DONTNEED MADV_FREE
+#else
+# define SANITIZER_MADVISE_DONTNEED MADV_DONTNEED
+#endif
 
 #endif // SANITIZER_PLATFORM_H

compiler-rt/trunk/lib/sanitizer_common/sanitizer_posix_libcdep.cc

uptr GetThreadSelf() {
   return (uptr)pthread_self();
 }
 
 void ReleaseMemoryPagesToOS(uptr beg, uptr end) {
   uptr page_size = GetPageSizeCached();
   uptr beg_aligned = RoundUpTo(beg, page_size);
   uptr end_aligned = RoundDownTo(end, page_size);
   if (beg_aligned < end_aligned)
-    madvise((void*)beg_aligned, end_aligned - beg_aligned, MADV_DONTNEED);
+    madvise((void *)beg_aligned, end_aligned - beg_aligned,
+            SANITIZER_MADVISE_DONTNEED);
 }
 
 void NoHugePagesInRegion(uptr addr, uptr size) {
 #ifdef MADV_NOHUGEPAGE  // May not be defined on old systems.
   madvise((void *)addr, size, MADV_NOHUGEPAGE);
 #endif  // MADV_NOHUGEPAGE
 }