[lld] 9509f4e - [LLD][COFF] Improve symbol table info for import thunk

[Martin Storsjö via llvm-commits]

Author: Alvin Wong
Date: 2022-09-20T10:44:45+03:00
New Revision: 9509f4e6578b78b6380a07c0b1c846b9c0d1682a

URL: https://github.com/llvm/llvm-project/commit/9509f4e6578b78b6380a07c0b1c846b9c0d1682a
DIFF: https://github.com/llvm/llvm-project/commit/9509f4e6578b78b6380a07c0b1c846b9c0d1682a.diff

LOG: [LLD][COFF] Improve symbol table info for import thunk

Import thunks themselves contain a jump or branch, which is code by
nature. Therefore the import thunk symbol should be marked as function
type in the symbol table to help with debugging.

The `__imp_` import symbol associated to the import thunk is also useful
for debugging. However, when the import symbol isn't directly referenced
outside of the import thunk, it doesn't normally get added to the symbol
table. This change teaches LLD to add the import symbol explicitly.

Reviewed By: mstorsjo

Differential Revision: https://reviews.llvm.org/D134169

Added: 
    

Modified: 
    lld/COFF/Writer.cpp
    lld/test/COFF/symtab.test

Removed: 
    


################################################################################
diff  --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 088384143e262..b3761baa707e2 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -1179,6 +1179,10 @@ Optional<coff_symbol16> Writer::createSymbol(Defined *def) {
     COFFSymbolRef ref = d->getCOFFSymbol();
     sym.Type = ref.getType();
     sym.StorageClass = ref.getStorageClass();
+  } else if (def->kind() == Symbol::DefinedImportThunkKind) {
+    sym.Type = (IMAGE_SYM_DTYPE_FUNCTION << SCT_COMPLEX_TYPE_SHIFT) |
+               IMAGE_SYM_TYPE_NULL;
+    sym.StorageClass = IMAGE_SYM_CLASS_EXTERNAL;
   } else {
     sym.Type = IMAGE_SYM_TYPE_NULL;
     sym.StorageClass = IMAGE_SYM_CLASS_EXTERNAL;
@@ -1225,6 +1229,14 @@ void Writer::createSymbolAndStringTable() {
 
         if (Optional<coff_symbol16> sym = createSymbol(d))
           outputSymtab.push_back(*sym);
+
+        if (auto *dthunk = dyn_cast<DefinedImportThunk>(d)) {
+          if (!dthunk->wrappedSym->writtenToSymtab) {
+            dthunk->wrappedSym->writtenToSymtab = true;
+            if (Optional<coff_symbol16> sym = createSymbol(dthunk->wrappedSym))
+              outputSymtab.push_back(*sym);
+          }
+        }
       }
     }
   }

diff  --git a/lld/test/COFF/symtab.test b/lld/test/COFF/symtab.test
index 949e9604bfd89..ccf26fde2027b 100644
--- a/lld/test/COFF/symtab.test
+++ b/lld/test/COFF/symtab.test
@@ -15,6 +15,15 @@
 # CHECK-NEXT:     Value: 80
 # CHECK-NEXT:     Section: .text (1)
 # CHECK-NEXT:     BaseType: Null (0x0)
+# CHECK-NEXT:     ComplexType: Function (0x2)
+# CHECK-NEXT:     StorageClass: External (0x2)
+# CHECK-NEXT:     AuxSymbolCount: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Symbol {
+# CHECK-NEXT:     Name: __imp_MessageBoxA
+# CHECK-NEXT:     Value:
+# CHECK-NEXT:     Section: .rdata (2)
+# CHECK-NEXT:     BaseType: Null (0x0)
 # CHECK-NEXT:     ComplexType: Null (0x0)
 # CHECK-NEXT:     StorageClass: External (0x2)
 # CHECK-NEXT:     AuxSymbolCount: 0
@@ -24,6 +33,15 @@
 # CHECK-NEXT:     Value: 64
 # CHECK-NEXT:     Section: .text (1)
 # CHECK-NEXT:     BaseType: Null (0x0)
+# CHECK-NEXT:     ComplexType: Function (0x2)
+# CHECK-NEXT:     StorageClass: External (0x2)
+# CHECK-NEXT:     AuxSymbolCount: 0
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Symbol {
+# CHECK-NEXT:     Name: __imp_ExitProcess
+# CHECK-NEXT:     Value:
+# CHECK-NEXT:     Section: .rdata (2)
+# CHECK-NEXT:     BaseType: Null (0x0)
 # CHECK-NEXT:     ComplexType: Null (0x0)
 # CHECK-NEXT:     StorageClass: External (0x2)
 # CHECK-NEXT:     AuxSymbolCount: 0