From: Lang Hames <lhames@gmail.com>
Date: Wed, 8 Sep 2021 12:30:08 +0000 (+1000)
Subject: [JITLink] Working memory shouldn't be subject to alignment constraints.
X-Git-Tag: upstream/15.0.7~31698
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=6c56b13331b4fa646ad5a46d36aa81557dfee007;p=platform%2Fupstream%2Fllvm.git

[JITLink] Working memory shouldn't be subject to alignment constraints.

Refactors copyBlockContentToWorkingMemory to use offsets rather than direct
pointers to working memory. This simplifies the problem of maintaining
alignments between blocks in working memory, without requiring the working
memory itself to be aligned.
---

diff --git a/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp b/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
index 5b163ab..8bb61a2 100644
--- a/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
+++ b/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
@@ -361,8 +361,6 @@ void JITLinkerBase::copyBlockContentToWorkingMemory(
 
     auto SegMem =
         Alloc.getWorkingMemory(static_cast<sys::Memory::ProtectionFlags>(Prot));
-    char *LastBlockEnd = SegMem.data();
-    char *BlockDataPtr = LastBlockEnd;
 
     LLVM_DEBUG({
       dbgs() << "  Processing segment "
@@ -372,53 +370,64 @@ void JITLinkerBase::copyBlockContentToWorkingMemory(
              << " ]\n    Processing content sections:\n";
     });
 
+    if (SegLayout.ContentBlocks.empty()) {
+      LLVM_DEBUG(dbgs() << "    No content blocks.\n");
+      continue;
+    }
+
+    size_t BlockOffset = 0;
+    size_t LastBlockEnd = 0;
+
     for (auto *B : SegLayout.ContentBlocks) {
       LLVM_DEBUG(dbgs() << "    " << *B << ":\n");
 
       // Pad to alignment/alignment-offset.
-      BlockDataPtr = alignToBlock(BlockDataPtr, *B);
+      BlockOffset = alignToBlock(BlockOffset, *B);
 
       LLVM_DEBUG({
-        dbgs() << "      Bumped block pointer to " << (const void *)BlockDataPtr
-               << " to meet block alignment " << B->getAlignment()
-               << " and alignment offset " << B->getAlignmentOffset() << "\n";
+        dbgs() << "      Bumped block offset to "
+               << formatv("{0:x}", BlockOffset) << " to meet block alignment "
+               << B->getAlignment() << " and alignment offset "
+               << B->getAlignmentOffset() << "\n";
       });
 
       // Zero pad up to alignment.
       LLVM_DEBUG({
-        if (LastBlockEnd != BlockDataPtr)
-          dbgs() << "      Zero padding from " << (const void *)LastBlockEnd
-                 << " to " << (const void *)BlockDataPtr << "\n";
+        if (LastBlockEnd != BlockOffset)
+          dbgs() << "      Zero padding from " << formatv("{0:x}", LastBlockEnd)
+                 << " to " << formatv("{0:x}", BlockOffset) << "\n";
       });
 
-      while (LastBlockEnd != BlockDataPtr)
-        *LastBlockEnd++ = 0;
+      for (; LastBlockEnd != BlockOffset; ++LastBlockEnd)
+        *(SegMem.data() + LastBlockEnd) = 0;
 
       // Copy initial block content.
       LLVM_DEBUG({
         dbgs() << "      Copying block " << *B << " content, "
                << B->getContent().size() << " bytes, from "
-               << (const void *)B->getContent().data() << " to "
-               << (const void *)BlockDataPtr << "\n";
+               << (const void *)B->getContent().data() << " to offset "
+               << formatv("{0:x}", BlockOffset) << "\n";
       });
-      memcpy(BlockDataPtr, B->getContent().data(), B->getContent().size());
+      memcpy(SegMem.data() + BlockOffset, B->getContent().data(),
+             B->getContent().size());
 
       // Point the block's content to the fixed up buffer.
-      B->setMutableContent({BlockDataPtr, B->getContent().size()});
+      B->setMutableContent(
+          {SegMem.data() + BlockOffset, B->getContent().size()});
 
       // Update block end pointer.
-      LastBlockEnd = BlockDataPtr + B->getContent().size();
-      BlockDataPtr = LastBlockEnd;
+      LastBlockEnd = BlockOffset + B->getContent().size();
+      BlockOffset = LastBlockEnd;
     }
 
     // Zero pad the rest of the segment.
     LLVM_DEBUG({
-      dbgs() << "    Zero padding end of segment from "
-             << (const void *)LastBlockEnd << " to "
-             << (const void *)((char *)SegMem.data() + SegMem.size()) << "\n";
+      dbgs() << "    Zero padding end of segment from offset "
+             << formatv("{0:x}", LastBlockEnd) << " to "
+             << formatv("{0:x}", SegMem.size()) << "\n";
     });
-    while (LastBlockEnd != SegMem.data() + SegMem.size())
-      *LastBlockEnd++ = 0;
+    for (; LastBlockEnd != SegMem.size(); ++LastBlockEnd)
+      *(SegMem.data() + LastBlockEnd) = 0;
   }
 }