[lld] Implement getOutputCharacteristics for non-section code thunks. (#70721)

This will be useful for ARM64EC, but it also fixes MinGW export handling
when synthetic function symbols are exported.

Author: cjacek

lld/COFF/Chunks.h

@@ -180,6 +180,16 @@ class NonSectionChunk : public Chunk {
   NonSectionChunk(Kind k = OtherKind) : Chunk(k) {}
 };
 
+class NonSectionCodeChunk : public NonSectionChunk {
+public:
+  virtual uint32_t getOutputCharacteristics() const override {
+    return llvm::COFF::IMAGE_SCN_MEM_READ | llvm::COFF::IMAGE_SCN_MEM_EXECUTE;
+  }
+
+protected:
+  NonSectionCodeChunk(Kind k = OtherKind) : NonSectionChunk(k) {}
+};
+
 // MinGW specific; information about one individual location in the image
 // that needs to be fixed up at runtime after loading. This represents
 // one individual element in the PseudoRelocTableChunk table.
@@ -508,10 +518,10 @@ static const uint8_t importThunkARM64[] = {
 // Windows-specific.
 // A chunk for DLL import jump table entry. In a final output, its
 // contents will be a JMP instruction to some __imp_ symbol.
-class ImportThunkChunk : public NonSectionChunk {
+class ImportThunkChunk : public NonSectionCodeChunk {
 public:
   ImportThunkChunk(COFFLinkerContext &ctx, Defined *s)
-      : NonSectionChunk(ImportThunkKind), impSymbol(s), ctx(ctx) {}
+      : NonSectionCodeChunk(ImportThunkKind), impSymbol(s), ctx(ctx) {}
   static bool classof(const Chunk *c) { return c->kind() == ImportThunkKind; }
 
 protected:
@@ -560,7 +570,7 @@ class ImportThunkChunkARM64 : public ImportThunkChunk {
   MachineTypes getMachine() const override { return ARM64; }
 };
 
-class RangeExtensionThunkARM : public NonSectionChunk {
+class RangeExtensionThunkARM : public NonSectionCodeChunk {
 public:
   explicit RangeExtensionThunkARM(COFFLinkerContext &ctx, Defined *t)
       : target(t), ctx(ctx) {
@@ -576,7 +586,7 @@ class RangeExtensionThunkARM : public NonSectionChunk {
   COFFLinkerContext &ctx;
 };
 
-class RangeExtensionThunkARM64 : public NonSectionChunk {
+class RangeExtensionThunkARM64 : public NonSectionCodeChunk {
 public:
   explicit RangeExtensionThunkARM64(COFFLinkerContext &ctx, Defined *t)
       : target(t), ctx(ctx) {

lld/COFF/DLL.cpp

@@ -313,7 +313,7 @@ static const uint8_t tailMergeARM64[] = {
 };
 
 // A chunk for the delay import thunk.
-class ThunkChunkX64 : public NonSectionChunk {
+class ThunkChunkX64 : public NonSectionCodeChunk {
 public:
   ThunkChunkX64(Defined *i, Chunk *tm) : imp(i), tailMerge(tm) {}
 
@@ -330,7 +330,7 @@ class ThunkChunkX64 : public NonSectionChunk {
   Chunk *tailMerge = nullptr;
 };
 
-class TailMergeChunkX64 : public NonSectionChunk {
+class TailMergeChunkX64 : public NonSectionCodeChunk {
 public:
   TailMergeChunkX64(Chunk *d, Defined *h) : desc(d), helper(h) {}
 
@@ -382,7 +382,7 @@ class TailMergeUnwindInfoX64 : public NonSectionChunk {
   }
 };
 
-class ThunkChunkX86 : public NonSectionChunk {
+class ThunkChunkX86 : public NonSectionCodeChunk {
 public:
   ThunkChunkX86(COFFLinkerContext &ctx, Defined *i, Chunk *tm)
       : imp(i), tailMerge(tm), ctx(ctx) {}
@@ -407,7 +407,7 @@ class ThunkChunkX86 : public NonSectionChunk {
   const COFFLinkerContext &ctx;
 };
 
-class TailMergeChunkX86 : public NonSectionChunk {
+class TailMergeChunkX86 : public NonSectionCodeChunk {
 public:
   TailMergeChunkX86(COFFLinkerContext &ctx, Chunk *d, Defined *h)
       : desc(d), helper(h), ctx(ctx) {}
@@ -432,7 +432,7 @@ class TailMergeChunkX86 : public NonSectionChunk {
   const COFFLinkerContext &ctx;
 };
 
-class ThunkChunkARM : public NonSectionChunk {
+class ThunkChunkARM : public NonSectionCodeChunk {
 public:
   ThunkChunkARM(COFFLinkerContext &ctx, Defined *i, Chunk *tm)
       : imp(i), tailMerge(tm), ctx(ctx) {
@@ -459,7 +459,7 @@ class ThunkChunkARM : public NonSectionChunk {
   const COFFLinkerContext &ctx;
 };
 
-class TailMergeChunkARM : public NonSectionChunk {
+class TailMergeChunkARM : public NonSectionCodeChunk {
 public:
   TailMergeChunkARM(COFFLinkerContext &ctx, Chunk *d, Defined *h)
       : desc(d), helper(h), ctx(ctx) {
@@ -486,7 +486,7 @@ class TailMergeChunkARM : public NonSectionChunk {
   const COFFLinkerContext &ctx;
 };
 
-class ThunkChunkARM64 : public NonSectionChunk {
+class ThunkChunkARM64 : public NonSectionCodeChunk {
 public:
   ThunkChunkARM64(Defined *i, Chunk *tm) : imp(i), tailMerge(tm) {
     setAlignment(4);
@@ -506,7 +506,7 @@ class ThunkChunkARM64 : public NonSectionChunk {
   Chunk *tailMerge = nullptr;
 };
 
-class TailMergeChunkARM64 : public NonSectionChunk {
+class TailMergeChunkARM64 : public NonSectionCodeChunk {
 public:
   TailMergeChunkARM64(Chunk *d, Defined *h) : desc(d), helper(h) {
     setAlignment(4);

lld/test/COFF/export-thunk.test

@@ -0,0 +1,14 @@
+REQUIRES: x86
+
+RUN: echo -e 'LIBRARY test.dll\nEXPORTS\nimpfunc\n' > %t.imp.def
+RUN: llvm-dlltool -m i386:x86-64 -d %t.imp.def -l %t.imp.lib
+RUN: lld-link -machine:amd64 -out:%t.dll -dll -noentry -lldmingw %t.imp.lib -export:impfunc -output-def:%t.def
+
+Check that the synthetic import thunk is exported as a function, not data.
+
+RUN: cat %t.def | FileCheck %s
+CHECK: EXPORTS
+CHECK-NEXT: impfunc @1
+
+RUN: cat %t.def | FileCheck -check-prefix=CHECK-NO-DATA %s
+CHECK-NO-DATA-NOT: DATA