[lld] 52fc6ff - [ELF] Refine isExported/isPreemptible condition
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 5 21:16:16 PST 2025
Author: Fangrui Song
Date: 2025-02-05T21:16:00-08:00
New Revision: 52fc6ffcda0895c0c7b976ad1f5cb5a282b571d2
URL: https://github.com/llvm/llvm-project/commit/52fc6ffcda0895c0c7b976ad1f5cb5a282b571d2
DIFF: https://github.com/llvm/llvm-project/commit/52fc6ffcda0895c0c7b976ad1f5cb5a282b571d2.diff
LOG: [ELF] Refine isExported/isPreemptible condition
Reland 994cea3f0a2d0caf4d66321ad5a06ab330144d89 after bolt tests no
longer rely on -pie --unresolved-symbols=ignore-all with no input DSO
generating PLT entries.
---
Commit f10441ad003236ef3b9e5415a571d2be0c0ce5ce , while dropping a
special case for isUndefWeak and --no-dynamic-linking, made
--export-dynamic ineffective when -pie is used without any input DSO.
This change restores --export-dynamic and unifies -pie and -pie
--no-dynamic-linker when there is no input DSO.
* -pie with no input DSO suppresses undefined symbols in .dynsym.
Previously this only appied to -pie --no-dynamic-linker.
* As a side effect, -pie with no input DSO suppresses PLT.
Added:
Modified:
lld/ELF/Config.h
lld/ELF/Driver.cpp
lld/ELF/Symbols.cpp
lld/ELF/SyntheticSections.cpp
lld/ELF/Writer.cpp
lld/test/ELF/executable-undefined-ignoreall.s
lld/test/ELF/ppc32-weak-undef-call.s
lld/test/ELF/ppc64-undefined-weak.s
lld/test/ELF/riscv-gp.s
lld/test/ELF/weak-undef-lib.s
lld/test/ELF/weak-undef-no-dynamic-linker.s
lld/test/ELF/weak-undef-rw.s
Removed:
################################################################################
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index a1ac0973bcc4028..3cdb400e423fd95 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -298,7 +298,6 @@ struct Config {
bool gdbIndex;
bool gnuHash = false;
bool gnuUnique;
- bool hasDynSymTab;
bool ignoreDataAddressEquality;
bool ignoreFunctionAddressEquality;
bool ltoCSProfileGenerate;
@@ -312,7 +311,6 @@ 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
index a14d3629f6eec0e..2835b86d05e9cc2 100644
--- 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();
}
@@ -2948,12 +2945,8 @@ 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
index 890877cb1bc0463..80b069142800725 100644
--- 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
index ffa6e3c008c48ed..b03c4282ab1aa5d 100644
--- 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
index 49077055e84fbf3..858f92c00115870 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -285,6 +285,7 @@ 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())
@@ -301,7 +302,8 @@ static void demoteSymbolsAndComputeIsPreemptible(Ctx &ctx) {
}
if (hasDynsym)
- sym->isPreemptible = (sym->isUndefined() || sym->isExported) &&
+ sym->isPreemptible = maybePreemptible &&
+ (sym->isUndefined() || sym->isExported) &&
computeIsPreemptible(ctx, *sym);
}
}
@@ -1940,10 +1942,9 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
if (ctx.in.symTab)
ctx.in.symTab->addSymbol(sym);
- // 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()) {
+ // computeBinding might localize a symbol that was considered exported
+ // but then synthesized as hidden (e.g. _DYNAMIC).
+ 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
index 073b22bd84543a6..1f83b1b61830a4f 100644
--- 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
index dfb45e5fe18cfd3..1ad280a49c038f1 100644
--- 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
index 7b1be5e36dd3278..e9168020b216fdf 100644
--- 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
index a30f5e9fbc6250a..2f715e1470f2da8 100644
--- 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
index a554e1d5a2f899d..0ff1bc755f0750b 100644
--- 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
index fa6936e1ef393fc..11abd5351af9de9 100644
--- 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
index ec3e4ce7348957e..c5cf1bdcaba68f4 100644
--- 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
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