[lld] b8a4780 - [ELF] Simplify and optimize SymbolTableSection<ELFT>::writeTo

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2021-12-27T15:16:14-08:00
New Revision: b8a47800321de538a39b92a2d539e1082e034e91

URL: https://github.com/llvm/llvm-project/commit/b8a47800321de538a39b92a2d539e1082e034e91
DIFF: https://github.com/llvm/llvm-project/commit/b8a47800321de538a39b92a2d539e1082e034e91.diff

LOG: [ELF] Simplify and optimize SymbolTableSection<ELFT>::writeTo

Added: 
    

Modified: 
    lld/ELF/SyntheticSections.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 86b2f33196ec9..b3da9c7881bef 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -2182,8 +2182,6 @@ static BssSection *getCommonSec(Symbol *sym) {
 }
 
 static uint32_t getSymSectionIndex(Symbol *sym) {
-  if (getCommonSec(sym))
-    return SHN_COMMON;
   assert(!(sym->needsCopy && sym->isObject()));
   if (!isa<Defined>(sym) || sym->needsCopy)
     return SHN_UNDEF;
@@ -2205,10 +2203,10 @@ template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *buf) {
     Symbol *sym = ent.sym;
     bool isDefinedHere = type == SHT_SYMTAB || sym->partition == partition;
 
-    // Set st_info and st_other.
-    eSym->st_other = 0;
+    // Set st_name, st_info and st_other.
+    eSym->st_name = ent.strTabOffset;
     eSym->setBindingAndType(sym->binding, sym->type);
-    eSym->setVisibility(sym->visibility);
+    eSym->st_other = sym->visibility;
 
     // The 3 most significant bits of st_other are used by OpenPOWER ABI.
     // See getPPC64GlobalEntryToLocalEntryOffset() for more details.
@@ -2219,30 +2217,29 @@ template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *buf) {
     else if (config->emachine == EM_AARCH64)
       eSym->st_other |= sym->stOther & STO_AARCH64_VARIANT_PCS;
 
-    eSym->st_name = ent.strTabOffset;
-    if (isDefinedHere)
-      eSym->st_shndx = getSymSectionIndex(ent.sym);
-    else
-      eSym->st_shndx = 0;
-
-    // Copy symbol size if it is a defined symbol. st_size is not significant
-    // for undefined symbols, so whether copying it or not is up to us if that's
-    // the case. We'll leave it as zero because by not setting a value, we can
-    // get the exact same outputs for two sets of input files that 
diff er only
-    // in undefined symbol size in DSOs.
-    if (eSym->st_shndx == SHN_UNDEF || !isDefinedHere)
-      eSym->st_size = 0;
-    else
-      eSym->st_size = sym->getSize();
-
-    // st_value is usually an address of a symbol, but that has a special
-    // meaning for uninstantiated common symbols (--no-define-common).
-    if (BssSection *commonSec = getCommonSec(ent.sym))
+    if (BssSection *commonSec = getCommonSec(sym)) {
+      // st_value is usually an address of a symbol, but that has a special
+      // meaning for uninstantiated common symbols (--no-define-common).
+      eSym->st_shndx = SHN_COMMON;
       eSym->st_value = commonSec->alignment;
-    else if (isDefinedHere)
-      eSym->st_value = sym->getVA();
-    else
-      eSym->st_value = 0;
+      eSym->st_size = cast<Defined>(sym)->size;
+    } else {
+      const uint32_t shndx = getSymSectionIndex(sym);
+      if (isDefinedHere) {
+        eSym->st_shndx = shndx;
+        eSym->st_value = sym->getVA();
+        // Copy symbol size if it is a defined symbol. st_size is not
+        // significant for undefined symbols, so whether copying it or not is up
+        // to us if that's the case. We'll leave it as zero because by not
+        // setting a value, we can get the exact same outputs for two sets of
+        // input files that 
diff er only in undefined symbol size in DSOs.
+        eSym->st_size = shndx != SHN_UNDEF ? cast<Defined>(sym)->size : 0;
+      } else {
+        eSym->st_shndx = 0;
+        eSym->st_value = 0;
+        eSym->st_size = 0;
+      }
+    }
 
     ++eSym;
   }
@@ -2293,7 +2290,7 @@ void SymtabShndxSection::writeTo(uint8_t *buf) {
   // we need to write actual index, otherwise, we must write SHN_UNDEF(0).
   buf += 4; // Ignore .symtab[0] entry.
   for (const SymbolTableEntry &entry : in.symTab->getSymbols()) {
-    if (getSymSectionIndex(entry.sym) == SHN_XINDEX)
+    if (!getCommonSec(entry.sym) && getSymSectionIndex(entry.sym) == SHN_XINDEX)
       write32(buf, entry.sym->getOutputSection()->sectionIndex);
     buf += 4;
   }