[PATCH] D113866: [LLD] [COFF] Omit IMAGE_SYM_CLASS_LABEL symbols from the PE symbol table

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo created this revision.
mstorsjo added reviewers: rnk, efriedma.
mstorsjo requested review of this revision.
Herald added a project: LLVM.

Also omit section definition symbols. This matches the condition for
symbols to omit from map files.

If we start producing lots of IMAGE_SYM_CLASS_LABEL symbols due to
D113865 <https://reviews.llvm.org/D113865>, it inflates the size of mingw style default linked binaries
(with dwarf debug info and a regular PE symbol table) a fair bit
(by 14% in one test).

By omitting these symbols, the size remains the same as before, and
by omitting the section definition symbols we further shrink the
mingw style unstripped binaries by 14% in one test.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D113866

Files:
  lld/COFF/Writer.cpp
  lld/test/COFF/strtab-size.s
  lld/test/COFF/symtab.test


Index: lld/test/COFF/symtab.test
===================================================================
--- lld/test/COFF/symtab.test
+++ lld/test/COFF/symtab.test
@@ -11,33 +11,6 @@
 
 # CHECK:      Symbols [
 # CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: .text
-# CHECK-NEXT:     Value: 0
-# CHECK-NEXT:     Section: .text (1)
-# CHECK-NEXT:     BaseType: Null (0x0)
-# CHECK-NEXT:     ComplexType: Null (0x0)
-# CHECK-NEXT:     StorageClass: Static (0x3)
-# CHECK-NEXT:     AuxSymbolCount: 0
-# CHECK-NEXT:   }
-# CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: .text2
-# CHECK-NEXT:     Value: 0
-# CHECK-NEXT:     Section: .text (1)
-# CHECK-NEXT:     BaseType: Null (0x0)
-# CHECK-NEXT:     ComplexType: Null (0x0)
-# CHECK-NEXT:     StorageClass: Static (0x3)
-# CHECK-NEXT:     AuxSymbolCount: 0
-# CHECK-NEXT:   }
-# CHECK-NEXT:   Symbol {
-# CHECK-NEXT:     Name: .data
-# CHECK-NEXT:     Value: 0
-# CHECK-NEXT:     Section: .data (3)
-# CHECK-NEXT:     BaseType: Null (0x0)
-# CHECK-NEXT:     ComplexType: Null (0x0)
-# CHECK-NEXT:     StorageClass: Static (0x3)
-# CHECK-NEXT:     AuxSymbolCount: 0
-# CHECK-NEXT:   }
-# CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: MessageBoxA
 # CHECK-NEXT:     Value: 80
 # CHECK-NEXT:     Section: .text (1)
@@ -235,4 +208,10 @@
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            .Ltemp_symbol
+    Value:           1
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
 ...
Index: lld/test/COFF/strtab-size.s
===================================================================
--- lld/test/COFF/strtab-size.s
+++ lld/test/COFF/strtab-size.s
@@ -213,4 +213,5 @@
 sym192:
 sym193:
 sym194:
+sym195:
   ret
Index: lld/COFF/Writer.cpp
===================================================================
--- lld/COFF/Writer.cpp
+++ lld/COFF/Writer.cpp
@@ -1210,6 +1210,13 @@
         auto *d = dyn_cast_or_null<Defined>(b);
         if (!d || d->writtenToSymtab)
           continue;
+        auto *dc = dyn_cast_or_null<DefinedCOFF>(d);
+        if (dc) {
+          COFFSymbolRef symRef = dc->getCOFFSymbol();
+          if (symRef.isSectionDefinition() ||
+              symRef.getStorageClass() == COFF::IMAGE_SYM_CLASS_LABEL)
+            continue;
+        }
         d->writtenToSymtab = true;
 
         if (Optional<coff_symbol16> sym = createSymbol(d))


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