[ELF] Refine isExported/isPreemptible condition

Commit f10441a dropped a special case for isUndefWeak and --no-dynamic-linking but also made --export-dynamic ineffective for static PIE. This change restores the --export-dynamic behavior and entirely drops special handling of --no-dynamic-linker: * -pie with no input DSO, similar to --no-dynamic-linker, suppresses undefined symbols in .dynsym The new behaviors resemble GNU ld more.
arm · Feb 1, 2025 · 994cea3 · 994cea3
1 parent 386af4a
commit 994cea3
Show file tree

Hide file tree

Showing 12 changed files with 46 additions and 48 deletions.
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
@@ -292,7 +292,6 @@ struct Config {
   bool gdbIndex;
   bool gnuHash = false;
   bool gnuUnique;
-  bool hasDynSymTab;
   bool ignoreDataAddressEquality;
   bool ignoreFunctionAddressEquality;
   bool ltoCSProfileGenerate;
@@ -306,7 +305,6 @@ struct Config {
   bool mipsN32Abi = false;
   bool mmapOutputFile;
   bool nmagic;
-  bool noDynamicLinker = false;
   bool noinhibitExec;
   bool nostdlib;
   bool oFormatBinary;

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
@@ -781,11 +781,8 @@ static StringRef getDynamicLinker(Ctx &ctx, opt::InputArgList &args) {
   auto *arg = args.getLastArg(OPT_dynamic_linker, OPT_no_dynamic_linker);
   if (!arg)
     return "";
-  if (arg->getOption().getID() == OPT_no_dynamic_linker) {
-    // --no-dynamic-linker suppresses undefined weak symbols in .dynsym
-    ctx.arg.noDynamicLinker = true;
+  if (arg->getOption().getID() == OPT_no_dynamic_linker)
     return "";
-  }
   return arg->getValue();
 }
 
@@ -2900,12 +2897,8 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
 
   parseFiles(ctx, files);
 
-  // Dynamic linking is used if there is an input DSO,
-  // or -shared or non-static pie is specified.
-  ctx.hasDynsym = !ctx.sharedFiles.empty() || ctx.arg.shared ||
-                  (ctx.arg.pie && !ctx.arg.noDynamicLinker);
   // Create dynamic sections for dynamic linking and static PIE.
-  ctx.arg.hasDynSymTab = ctx.hasDynsym || ctx.arg.isPic;
+  ctx.hasDynsym = !ctx.sharedFiles.empty() || ctx.arg.isPic;
 
   // If an entry symbol is in a static archive, pull out that file now.
   if (Symbol *sym = ctx.symtab->find(ctx.arg.entry))

diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
@@ -360,7 +360,9 @@ void elf::parseVersionAndComputeIsPreemptible(Ctx &ctx) {
   // Symbol themselves might know their versions because symbols
   // can contain versions in the form of <name>@<version>.
   // Let them parse and update their names to exclude version suffix.
+  // In addition, compute isExported and isPreemptible.
   bool hasDynsym = ctx.hasDynsym;
+  bool maybePreemptible = ctx.sharedFiles.size() || ctx.arg.shared;
   for (Symbol *sym : ctx.symtab->getSymbols()) {
     if (sym->hasVersionSuffix)
       sym->parseSymbolVersion(ctx);
@@ -371,7 +373,7 @@ void elf::parseVersionAndComputeIsPreemptible(Ctx &ctx) {
       continue;
     }
     if (!sym->isDefined() && !sym->isCommon()) {
-      sym->isPreemptible = computeIsPreemptible(ctx, *sym);
+      sym->isPreemptible = maybePreemptible && computeIsPreemptible(ctx, *sym);
     } else if (ctx.arg.exportDynamic &&
                (sym->isUsedInRegularObj || !sym->ltoCanOmit)) {
       sym->isExported = true;

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
@@ -4740,7 +4740,7 @@ template <class ELFT> void elf::createSyntheticSections(Ctx &ctx) {
 
   // Add MIPS-specific sections.
   if (ctx.arg.emachine == EM_MIPS) {
-    if (!ctx.arg.shared && ctx.arg.hasDynSymTab) {
+    if (!ctx.arg.shared && ctx.hasDynsym) {
       ctx.in.mipsRldMap = std::make_unique<MipsRldMapSection>(ctx);
       add(*ctx.in.mipsRldMap);
     }
@@ -4803,7 +4803,7 @@ template <class ELFT> void elf::createSyntheticSections(Ctx &ctx) {
       part.relaDyn = std::make_unique<RelocationSection<ELFT>>(
           ctx, relaDynName, ctx.arg.zCombreloc, threadCount);
 
-    if (ctx.arg.hasDynSymTab) {
+    if (ctx.hasDynsym) {
       add(*part.dynSymTab);
 
       part.verSym = std::make_unique<VersionTableSection>(ctx);

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
@@ -284,6 +284,7 @@ static void demoteSymbolsAndComputeIsPreemptible(Ctx &ctx) {
   llvm::TimeTraceScope timeScope("Demote symbols");
   DenseMap<InputFile *, DenseMap<SectionBase *, size_t>> sectionIndexMap;
   bool hasDynsym = ctx.hasDynsym;
+  bool maybePreemptible = ctx.sharedFiles.size() || ctx.arg.shared;
   for (Symbol *sym : ctx.symtab->getSymbols()) {
     if (auto *d = dyn_cast<Defined>(sym)) {
       if (d->section && !d->section->isLive())
@@ -300,7 +301,8 @@ static void demoteSymbolsAndComputeIsPreemptible(Ctx &ctx) {
     }
 
     if (hasDynsym)
-      sym->isPreemptible = (sym->isUndefined() || sym->isExported) &&
+      sym->isPreemptible = maybePreemptible &&
+                           (sym->isUndefined() || sym->isExported) &&
                            computeIsPreemptible(ctx, *sym);
   }
 }
@@ -1931,8 +1933,7 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
 
       // computeBinding might localize a linker-synthesized hidden symbol
       // (e.g. __global_pointer$) that was considered exported.
-      if (ctx.hasDynsym && (sym->isUndefined() || sym->isExported) &&
-          !sym->isLocal()) {
+      if ((sym->isExported || sym->isPreemptible) && !sym->isLocal()) {
         ctx.partitions[sym->partition - 1].dynSymTab->addSymbol(sym);
         if (auto *file = dyn_cast<SharedFile>(sym->file))
           if (file->isNeeded && !sym->isUndefined())

diff --git a/lld/test/ELF/executable-undefined-ignoreall.s b/lld/test/ELF/executable-undefined-ignoreall.s
@@ -1,11 +1,13 @@
 # REQUIRES: x86
 
-## --unresolved-symbols=ignore-all behaves similar to -shared:
+## In dynamic linking, --unresolved-symbols=ignore-all behaves similar to -shared:
 ## for PLT relocations to undefined symbols, produce dynamic relocations if we
 ## emit .dynsym.
 
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %S/Inputs/shared.s -o %ta.o
+# RUN: ld.lld -shared -soname=ta %ta.o -o %ta.so
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
-# RUN: ld.lld %t.o -o %t --unresolved-symbols=ignore-all -pie
+# RUN: ld.lld %t.o %ta.so -o %t --unresolved-symbols=ignore-all -pie
 # RUN: llvm-readobj -r %t | FileCheck %s
 
 # CHECK:      Relocations [

diff --git a/lld/test/ELF/ppc32-weak-undef-call.s b/lld/test/ELF/ppc32-weak-undef-call.s
@@ -1,15 +1,15 @@
 # REQUIRES: ppc
 # RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
 # RUN: ld.lld %t.o -o %t
-# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=PDE %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=STATIC %s
 # RUN: ld.lld -pie %t.o -o %t
-# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=PIC %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=STATIC %s
 # RUN: ld.lld -shared %t.o -o %t
 # RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=PIC %s
 
 ## It does not really matter how we fixup it, but we cannot overflow and
 ## should not generate a call stub (this would waste space).
-# PDE: bl 0x100100b4
+# STATIC: bl {{.*}} <.text>
 
 ## With -pie or -shared, create a call stub. ld.bfd produces bl .+0
 # PIC:       bl 0x[[PLT:[0-9a-f]+]]

diff --git a/lld/test/ELF/ppc64-undefined-weak.s b/lld/test/ELF/ppc64-undefined-weak.s
@@ -2,25 +2,25 @@
 
 # RUN: llvm-mc -filetype=obj -triple=powerpc64le %s -o %t.o
 # RUN: ld.lld %t.o -o %t
-# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s --check-prefix=PDE
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s --check-prefix=STATIC
 # RUN: ld.lld -pie %t.o -o %t
-# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s --check-prefix=PIC
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s --check-prefix=STATIC
 # RUN: ld.lld -shared %t.o -o %t.so
 # RUN: llvm-objdump -d --no-show-raw-insn %t.so | FileCheck %s --check-prefix=PIC
 
 # RUN: llvm-mc -filetype=obj -triple=powerpc64 %s -o %t.o
 # RUN: ld.lld %t.o -o %t
-# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s --check-prefix=PDE
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s --check-prefix=STATIC
 
 ## Branches to an undefined weak symbol need a thunk iff a dynamic relocation is
 ## produced. undefweak2 is hidden and does not need a dynamic relocation, so we
 ## suppress the thunk. undefweak1 needs a thunk iff -pie or -shared.
 
-# PDE-LABEL: <_start>:
-# PDE-NEXT:    bl {{.*}} <_start>
-# PDE-NEXT:    nop
-# PDE-NEXT:    bl {{.*}} <_start+0x8>
-# PDE-NEXT:    nop
+# STATIC-LABEL: <_start>:
+# STATIC-NEXT:    bl {{.*}} <_start>
+# STATIC-NEXT:    nop
+# STATIC-NEXT:    bl {{.*}} <_start+0x8>
+# STATIC-NEXT:    nop
 
 # PIC-LABEL: <_start>:
 # PIC-NEXT:    bl {{.*}} <__plt_undefweak1>

diff --git a/lld/test/ELF/riscv-gp.s b/lld/test/ELF/riscv-gp.s
@@ -14,17 +14,20 @@
 # SEC32: {{0*}}000039c0 0 NOTYPE GLOBAL DEFAULT [[#SDATA]] __global_pointer$
 
 # SEC64: [ [[#SDATA:]]] .sdata PROGBITS {{0*}}000032e0
+# SEC64:     '.dynsym'
+# SEC64-NOT: __global_pointer$
+# SEC64:     '.symtab'
 # SEC64: {{0*}}00003ae0 0 NOTYPE GLOBAL DEFAULT [[#SDATA]] __global_pointer$
 
 # ERR: error: relocation R_RISCV_PCREL_HI20 cannot be used against symbol '__global_pointer$'; recompile with -fPIC
 
 # RUN: ld.lld -pie --no-dynamic-linker --export-dynamic %t.64.o -o %t.64e
-# RUN: llvm-readelf -s %t.64e | FileCheck %s --check-prefix=STATICPIE
+# RUN: llvm-readelf -s %t.64e | FileCheck %s --check-prefix=STATICE
 
-# STATICPIE:     '.dynsym'
-# STATICPIE-NOT: __global_pointer$
-# STATICPIE:     '.symtab'
-# STATICPIE:     __global_pointer$
+# STATICE:     '.dynsym'
+# STATICE:     __global_pointer$
+# STATICE:     '.symtab'
+# STATICE:     __global_pointer$
 
 ## -r mode does not define __global_pointer$.
 # RUN: ld.lld -r %t.64.o -o %t.64.ro

diff --git a/lld/test/ELF/weak-undef-lib.s b/lld/test/ELF/weak-undef-lib.s
@@ -7,7 +7,7 @@
 # RUN: llvm-readobj --dyn-syms %t.so | FileCheck %s
 
 # RUN: ld.lld -pie -o %t %t1.o --start-lib %t2.o
-# RUN: llvm-readobj --dyn-syms %t | FileCheck %s
+# RUN: llvm-readelf --dyn-syms %t | FileCheck %s --check-prefix=STATICPIE
 
 # CHECK:      Name: foo
 # CHECK-NEXT: Value: 0x0

diff --git a/lld/test/ELF/weak-undef-no-dynamic-linker.s b/lld/test/ELF/weak-undef-no-dynamic-linker.s
@@ -1,13 +1,12 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
 # RUN: ld.lld -pie %t.o -o %t
-# RUN: llvm-readobj --dyn-syms %t | FileCheck %s
+# RUN: llvm-readobj --dyn-syms %t | FileCheck --check-prefix=NO %s
 # RUN: ld.lld -pie --no-dynamic-linker %t.o -o %t
 # RUN: llvm-readobj --dyn-syms %t | FileCheck --check-prefix=NO %s
 
-## With --no-dynamic-linker, don't emit undefined weak symbols to .dynsym .
-## This will suppress a relocation.
-# CHECK: Name: foo
+## With static PIE (whether or not --no-dynamic-linker is specified), don't
+## emit undefined weak symbols to .dynsym . This suppresses relocations.
 # NO-NOT: Name: foo
 
 .weak foo

diff --git a/lld/test/ELF/weak-undef-rw.s b/lld/test/ELF/weak-undef-rw.s
@@ -1,23 +1,23 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 # RUN: ld.lld %t.o -o %t --export-dynamic
-# RUN: llvm-readelf -r --hex-dump=.data %t | FileCheck %s --check-prefix=NOPIC
+# RUN: llvm-readelf -r --hex-dump=.data %t | FileCheck %s --check-prefix=STATIC
 # RUN: ld.lld %t.o -o %t.pie -pie
-# RUN: llvm-readobj -r %t.pie | FileCheck %s --check-prefix=PIC
+# RUN: llvm-readelf -r --hex-dump=.data %t.pie | FileCheck %s --check-prefix=STATIC
 # RUN: ld.lld %t.o -o %t.so -shared
 # RUN: llvm-readobj -r %t.so | FileCheck %s --check-prefix=PIC
 
 ## gABI leaves the behavior of weak undefined references implementation defined.
-## We choose to resolve them statically for -no-pie and produce dynamic relocations
-## for -pie and -shared.
+## We choose to resolve them statically for static linking and produce dynamic relocations
+## for dynamic linking (-shared or at least one input DSO).
 ##
 ## Note: Some ports of GNU ld support -z nodynamic-undefined-weak that we don't
 ## implement.
 
-# NOPIC: no relocations
-# NOPIC: Hex dump of section '.data':
-# NOPIC-NEXT: {{.*}} 00000000 00000000 
-# NOPIC-EMPTY:
+# STATIC:      no relocations
+# STATIC:      Hex dump of section '.data':
+# STATIC-NEXT: {{.*}} 00000000 00000000 .
+# STATIC-EMPTY:
 
 # PIC:      .rela.dyn {
 # PIC-NEXT:   R_X86_64_64 foobar 0x0