[RuntimeDyld] Make sure code-sections aren't under-aligned.

Code-section alignment should be at least as high as the minimum
stub alignment. If the section alignment is lower it can cause
padding to be emitted resulting in alignment errors if the section
is mapped to a higher alignment on the target.

E.g. If a text section with a 4-byte alignment gets 4-bytes of
padding to guarantee 8-byte alignment for stubs but is re-mapped to
an 8-byte alignment on the target, the 4-bytes of padding will push
the stubs to 4-byte alignment causing a crash.

No test case: There is currently no way to control host section
alignment in llvm-rtdyld. This could be made testable by adding
a custom memory manager. I'll look at that in a follow-up patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245031 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp b/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
index de094066d36de620fb2cbbd9c7ceb5ec20a42cc3..42a0205331b031974d08cba4ceee4bed9f61602d 100644 (file)
--- a/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
+++ b/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
@@ -564,6 +564,12 @@ unsigned RuntimeDyldImpl::emitSection(const ObjectFile &Obj,
   if (!IsVirtual)
     pData = data.data();
 
+  // Code section alignment needs to be at least as high as stub alignment or
+  // padding calculations may by incorrect when the section is remapped to a
+  // higher alignment.
+  if (IsCode)
+    Alignment = std::max(Alignment, getStubAlignment());
+
   // Some sections, such as debug info, don't need to be loaded for execution.
   // Leave those where they are.
   if (IsRequired) {