[lld] d703b92 - [LLD] [COFF] Omit section symbols and IMAGE_SYM_CLASS_LABEL from the PE symbol table

[Martin Storsjö via llvm-commits]

Author: Martin Storsjö
Date: 2021-11-23T10:17:04+02:00
New Revision: d703b922961e0d02a5effdd4bfbb23ad50a3cc9f

URL: https://github.com/llvm/llvm-project/commit/d703b922961e0d02a5effdd4bfbb23ad50a3cc9f
DIFF: https://github.com/llvm/llvm-project/commit/d703b922961e0d02a5effdd4bfbb23ad50a3cc9f.diff

LOG: [LLD] [COFF] Omit section symbols and IMAGE_SYM_CLASS_LABEL from the PE symbol table

The section symbols aren't of much practical use when looking at
a linked image. This shrinks one observed mingw style unstripped
binary by 14%.

IMAGE_SYM_CLASS_LABEL is in spirit the same as a temporary assembler
label that isn't emitted on the object file level at all.

Differential Revision: https://reviews.llvm.org/D113866

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 600d14034dea8..0788f3519f4e0 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -1211,6 +1211,12 @@ void Writer::createSymbolAndStringTable() {
         if (!d || d->writtenToSymtab)
           continue;
         d->writtenToSymtab = true;
+        if (auto *dc = dyn_cast_or_null<DefinedCOFF>(d)) {
+          COFFSymbolRef symRef = dc->getCOFFSymbol();
+          if (symRef.isSectionDefinition() ||
+              symRef.getStorageClass() == COFF::IMAGE_SYM_CLASS_LABEL)
+            continue;
+        }
 
         if (Optional<coff_symbol16> sym = createSymbol(d))
           outputSymtab.push_back(*sym);

diff  --git a/lld/test/COFF/strtab-size.s b/lld/test/COFF/strtab-size.s
index 574b1a0265ba6..153363baf8c71 100644
--- a/lld/test/COFF/strtab-size.s
+++ b/lld/test/COFF/strtab-size.s
@@ -213,4 +213,5 @@ sym191:
 sym192:
 sym193:
 sym194:
+sym195:
   ret

diff  --git a/lld/test/COFF/symtab.test b/lld/test/COFF/symtab.test
index 1d47def32c8fc..949e9604bfd89 100644
--- a/lld/test/COFF/symtab.test
+++ b/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 @@ symbols:
     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
 ...