commit 1c897fec44a6abc6cd13c72b571a13fffbab3d90
author Martin Storsjö <martin@martin.st> Sat Nov 13 10:13:42 2021 +0200
committer Copybara-Service <copybara-worker@google.com> Tue Nov 23 00:41:05 2021 -0800
tree 5df03aebb960b1a20ba29d8a75abf9ae7ba1d7d4
parent 151cb57913e4d9ef5254fd636724878a46f713e9

[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

GitOrigin-RevId: d703b922961e0d02a5effdd4bfbb23ad50a3cc9f

COFF/Writer.cpp

diff --git a/COFF/Writer.cpp b/COFF/Writer.cpp
index 600d140..0788f35 100644
--- a/COFF/Writer.cpp
+++ b/COFF/Writer.cpp
@@ -1211,6 +1211,12 @@
         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);

test/COFF/strtab-size.s

diff --git a/test/COFF/strtab-size.s b/test/COFF/strtab-size.s
index 574b1a0..153363b 100644
--- a/test/COFF/strtab-size.s
+++ b/test/COFF/strtab-size.s
@@ -213,4 +213,5 @@
 sym192:
 sym193:
 sym194:
+sym195:
   ret

test/COFF/symtab.test

diff --git a/test/COFF/symtab.test b/test/COFF/symtab.test
index 1d47def..949e960 100644
--- a/test/COFF/symtab.test
+++ b/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
 ...