[lld] r349849 - [ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 20 14:46:01 PST 2018
Author: maskray
Date: Thu Dec 20 14:46:01 2018
New Revision: 349849
URL: http://llvm.org/viewvc/llvm-project?rev=349849&view=rev
Log:
[ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj
Summary:
In glibc, libc.so is a linker script with an as-needed dependency on ld-linux-x86-64.so.2
GROUP ( /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc_nonshared.a AS_NEEDED ( /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ) )
ld-linux-x86-64.so.2 (as-needed) defines some symbols which resolve undefined references in libc.so.6, it will therefore be added as a DT_NEEDED entry, which isn't necessary.
The test case as-needed-not-in-regular.s emulates the libc.so scenario, where ld.bfd and gold don't add DT_NEEDED for a.so
The relevant code in gold/resolve.cc:
// If we have a non-WEAK reference from a regular object to a
// dynamic object, mark the dynamic object as needed.
if (to->is_from_dynobj() && to->in_reg() && !to->is_undef_binding_weak())
to->object()->set_is_needed();
in_reg() appears to do something similar to IsUsedInRegularObj.
This patch makes lld do the similar thing, but moves the check from
addShared to a later stage MarkLive where all symbols are scanned.
Reviewers: ruiu, pcc, espindola
Reviewed By: ruiu
Subscribers: emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D55902
Added:
lld/trunk/test/ELF/as-needed-in-regular.s
lld/trunk/test/ELF/as-needed-not-in-regular.s
Modified:
lld/trunk/ELF/MarkLive.cpp
lld/trunk/ELF/SymbolTable.cpp
Modified: lld/trunk/ELF/MarkLive.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/MarkLive.cpp?rev=349849&r1=349848&r2=349849&view=diff
==============================================================================
--- lld/trunk/ELF/MarkLive.cpp (original)
+++ lld/trunk/ELF/MarkLive.cpp Thu Dec 20 14:46:01 2018
@@ -267,10 +267,16 @@ template <class ELFT> static void doGcSe
// 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;
}
Modified: lld/trunk/ELF/SymbolTable.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=349849&r1=349848&r2=349849&view=diff
==============================================================================
--- lld/trunk/ELF/SymbolTable.cpp (original)
+++ lld/trunk/ELF/SymbolTable.cpp Thu Dec 20 14:46:01 2018
@@ -503,14 +503,11 @@ void SymbolTable::addShared(StringRef Na
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;
}
}
Added: lld/trunk/test/ELF/as-needed-in-regular.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/as-needed-in-regular.s?rev=349849&view=auto
==============================================================================
--- lld/trunk/test/ELF/as-needed-in-regular.s (added)
+++ lld/trunk/test/ELF/as-needed-in-regular.s Thu Dec 20 14:46:01 2018
@@ -0,0 +1,24 @@
+# REQUIRES: x86
+
+# RUN: echo '.globl a; .type a, @function; .type a, @function; a: 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: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o --as-needed %ta.so -o %t
+# RUN: llvm-readelf -d %t | FileCheck %s
+# RUN: ld.lld %t.o --as-needed %ta.so --gc-sections -o %t
+# RUN: llvm-readelf -d %t | FileCheck %s
+
+# The order of %ta.so and %t.o does not matter.
+
+# RUN: ld.lld --as-needed %ta.so %t.o -o %t
+# RUN: llvm-readelf -d %t | FileCheck %s
+# RUN: ld.lld --as-needed %ta.so %t.o --gc-sections -o %t
+# RUN: llvm-readelf -d %t | FileCheck %s
+
+# CHECK: a.so
+
+.global _start
+_start:
+ jmp a at PLT
Added: lld/trunk/test/ELF/as-needed-not-in-regular.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/as-needed-not-in-regular.s?rev=349849&view=auto
==============================================================================
--- lld/trunk/test/ELF/as-needed-not-in-regular.s (added)
+++ lld/trunk/test/ELF/as-needed-not-in-regular.s Thu Dec 20 14:46:01 2018
@@ -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
More information about the llvm-commits
mailing list