Align ClearShadowForThreadStackAndTLS for NetBSD/i386

[krytarowski]

Summary

The static TLS vector for the main thread on NetBSD/i386 can be
unaligned in terms of the shadow granularity. Align the start of it with
Round Down and end of it with Round Up operations for the shadow
granularity shift.

Example static TLS vector ranges on NetBSD/i386:
tls_begin_=0xfbee7244 tls_end_=0xfbee726c.

ClearShadowForThreadStackAndTLS() is called from the Main Thread
bootstrap functions.

This change restores the NetBSD x86 32-bit (i386) support.

Sponsored by <The NetBSD Foundation>

[krytarowski]

Typo.

[joerg]

This looks sensible, but I don't know what PoisonShadow will do for the rest of the memory block.

[vitalybuka]

01-07 shadow values are used for partially addressable blocks. Problem that only lowest bytes can be addressable, and highest are poisoned. So you must to alight tls_begin_.
But you don't have to do so fo the tls_end_, it will be handled by partial values.

[krytarowski]

I need to align both in order to make it to work.

Otherwise, I'm observing:

==28177==AddressSanitizer CHECK failed: /public/llvm/projects/compiler-rt/lib/asan/asan_poisoning.cc:38 "((AddrIsAlignedByGranularity(addr + size))) != (0)" (0x0, 0x0)

[vitalybuka]

I see.
following should work, but I don't insist

FastPoisonShadowPartialRightRedzone(tls_begin_aligned, tls_end_ - tls_begin_aligned, tls_end_aligned - tls_end_, 0 /*does not matter, should not be used*/)

In D46585#1096044, @krytarowski wrote:

I need to align both in order to make it to work.

Otherwise, I'm observing:

==28177==AddressSanitizer CHECK failed: /public/llvm/projects/compiler-rt/lib/asan/asan_poisoning.cc:38 "((AddrIsAlignedByGranularity(addr + size))) != (0)" (0x0, 0x0)

lib/asan/asan_thread.cc

void AsanThread::SetThreadStackAndTls(const InitOptions *options) {
   int local;
   CHECK(AddrIsInStack((uptr)&local));
 }
 
 #endif  // !SANITIZER_FUCHSIA
 
 void AsanThread::ClearShadowForThreadStackAndTLS() {
   PoisonShadow(stack_bottom_, stack_top_ - stack_bottom_, 0);
-  if (tls_begin_ != tls_end_)
-    PoisonShadow(tls_begin_, tls_end_ - tls_begin_, 0);
+  if (tls_begin_ != tls_end_aligned) {
+    uptr tls_begin_aligned = RoundDownTo(tls_begin_, SHADOW_GRANULARITY);
+    uptr tls_end_aligned = RoundUpTo(tls_end_, SHADOW_GRANULARITY);
+    PoisonShadow(tls_begin_aligned, tls_end_aligned - tls_begin_aligned, 0);
+  }
 }
 
 bool AsanThread::GetStackFrameAccessByAddr(uptr addr,
                                            StackFrameAccess *access) {
   uptr bottom = 0;
   if (AddrIsInStack(addr)) {
     bottom = stack_bottom();
   } else if (has_fake_stack()) {