[PATCH] D53128: [LLD] [COFF] Set proper pointer size alignment for LocalImportChunk

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo created this revision.
mstorsjo added reviewers: ruiu, rnk, dmajor.
Herald added a reviewer: javed.absar.
Herald added a subscriber: kristof.beyls.

When these are accessed with load/store instructions on ARM64, it becomes strictly necessary to have them properly aligned.

This fixes PR39228.

This is, IMO, a good candidate for backporting to the 7.0.1 branch.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D53128

Files:
  COFF/Chunks.h
  test/COFF/arm64-localimport-align.s


Index: test/COFF/arm64-localimport-align.s
===================================================================
--- /dev/null
+++ test/COFF/arm64-localimport-align.s
@@ -0,0 +1,24 @@
+// REQUIRES: aarch64
+// RUN: llvm-mc -filetype=obj -triple=aarch64-windows %s -o %t.obj
+// RUN: lld-link -entry:main -subsystem:console %t.obj -out:%t.exe
+// Don't check the output, just make sure it links fine and doesn't
+// error out due to a misaligned load.
+    .text
+    .globl main
+    .globl myfunc
+main:
+    adrp x8, __imp_myfunc
+    ldr  x0, [x8, :lo12:__imp_myfunc]
+    br   x0
+    ret
+myfunc:
+    ret
+
+    .section .rdata, "dr"
+    // Start the .rdata section with a 4 byte chunk, to expose the alignment
+    // of the next chunk in the section.
+mydata:
+    .byte 42
+    // The synthesized LocalImportChunk gets stored here in the .rdata
+    // section, but needs to get proper 8 byte alignment since it is a
+    // pointer, just like regular LookupChunks in the IAT.
Index: COFF/Chunks.h
===================================================================
--- COFF/Chunks.h
+++ COFF/Chunks.h
@@ -368,7 +368,9 @@
 // See comments for DefinedLocalImport class.
 class LocalImportChunk : public Chunk {
 public:
-  explicit LocalImportChunk(Defined *S) : Sym(S) {}
+  explicit LocalImportChunk(Defined *S) : Sym(S) {
+    Alignment = getSize();
+  }
   size_t getSize() const override;
   void getBaserels(std::vector<Baserel> *Res) override;
   void writeTo(uint8_t *Buf) const override;


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