[RuntimeDyld] fix too-small-bitmask error

[nickdesaulniers]

Summary

This was flagged in https://www.viva64.com/en/b/0629/ under "Snippet No.
33".

It seems that this statement is doing the standard bitwise trick for
adjusting a value to have a specific alignment.

The issue is that getStubAlignment() returns an unsigned, while DataSize
is declared a uint64_t. The right hand side of the expression is not
extended to 64b before bitwise negation, resulting in the top half of
the mask being 0s, which is not correct for realignment.

[MaskRay]

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

845

How about DataSize &= -(uint64_t)getStubAlignment(); ?

[nickdesaulniers]

• use @MaskRay's trick

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

if (IsRequired || ProcessAllSections) {
     if (PaddingSize != 0) {
       memset(Addr + DataSize, 0, PaddingSize);
       // Update the DataSize variable to include padding.
       DataSize += PaddingSize;
 
       // Align DataSize to stub alignment if we have any stubs (PaddingSize will
       // have been increased above to account for this).
       if (StubBufSize > 0)
-        DataSize &= ~(getStubAlignment() - 1);
+        DataSize &= -(uint64_t)getStubAlignment();
     }
 
     LLVM_DEBUG(dbgs() << "emitSection SectionID: " << SectionID << " Name: "
                       << Name << " obj addr: " << format("%p", pData)
                       << " new addr: " << format("%p", Addr) << " DataSize: "
                       << DataSize << " StubBufSize: " << StubBufSize
                       << " Allocate: " << Allocate << "\n");
   } else {