[PATCH] D55902: [ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 179157.
MaskRay retitled this revision from "[ELF] SymbolTable::addShared: don't set IsNeeded unless IsUsedInRegularObj" to "[ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj".
MaskRay edited the summary of this revision.
MaskRay added a comment.

Move logic to MarkLive


Repository:
  rLLD LLVM Linker

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D55902/new/

https://reviews.llvm.org/D55902

Files:
  ELF/MarkLive.cpp
  ELF/SymbolTable.cpp
  test/ELF/as-needed-not-in-regular.s


Index: test/ELF/as-needed-not-in-regular.s
===================================================================
--- /dev/null
+++ test/ELF/as-needed-not-in-regular.s
@@ -0,0 +1,26 @@
+# REQUIRES: x86
+
+# RUN: echo '.globl a1, a2; .type a1, @function; .type a2, @function; a1: a2: ret' | \
+# RUN:   llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %ta.o
+# RUN: ld.lld %ta.o --shared --soname=a.so -o %ta.so
+
+# RUN: echo '.globl b; .type b, @function; b: jmp a1 at PLT' | \
+# RUN:   llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %tb.o
+# RUN: ld.lld %tb.o %ta.so --shared --soname=b.so -o %tb.so
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o %tb.so --as-needed %ta.so -o %t
+# RUN: llvm-readelf -d %t | FileCheck %s
+
+# RUN: ld.lld %t.o %tb.so --as-needed %ta.so --gc-sections -o %t
+# RUN: llvm-readelf -d %t | FileCheck %s
+
+# The symbol a1 (defined in a.so) is not referenced by a regular object,
+# the reference to a2 is weak, don't add a DT_NEEDED entry for a.so.
+# CHECK-NOT: a.so
+
+.global _start
+.weak a2
+_start:
+  jmp b at PLT
+  jmp a2
Index: ELF/SymbolTable.cpp
===================================================================
--- ELF/SymbolTable.cpp
+++ ELF/SymbolTable.cpp
@@ -503,14 +503,11 @@
 
   if ((S->isUndefined() || S->isLazy()) && S->Visibility == STV_DEFAULT) {
     uint8_t Binding = S->Binding;
-    bool WasUndefined = S->isUndefined();
     replaceSymbol<SharedSymbol>(S, File, Name, Sym.getBinding(), Sym.st_other,
                                 Sym.getType(), Sym.st_value, Sym.st_size,
                                 Alignment, VerdefIndex);
 
     S->Binding = Binding;
-    if (!S->isWeak() && !Config->GcSections && WasUndefined)
-      File.IsNeeded = true;
   }
 }
 
Index: ELF/MarkLive.cpp
===================================================================
--- ELF/MarkLive.cpp
+++ ELF/MarkLive.cpp
@@ -267,10 +267,16 @@
 // input sections. This function make some or all of them on
 // so that they are emitted to the output file.
 template <class ELFT> void elf::markLive() {
-  // If -gc-sections is missing, no sections are removed.
   if (!Config->GcSections) {
+    // If -gc-sections is missing, no sections are removed.
     for (InputSectionBase *Sec : InputSections)
       Sec->Live = true;
+
+    // If a DSO defines a symbol referenced in a regular object, it is needed.
+    for (Symbol *Sym : Symtab->getSymbols())
+      if (auto *S = dyn_cast<SharedSymbol>(Sym))
+        if (S->IsUsedInRegularObj && !S->isWeak())
+          S->getFile<ELFT>().IsNeeded = true;
     return;
   }
 


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