[lld] r319008 - [ELF] Do not keep symbols if they referenced only from discarded sections.
Igor Kudrin via llvm-commits
llvm-commits at lists.llvm.org
Sun Nov 26 21:51:10 PST 2017
Author: ikudrin
Date: Sun Nov 26 21:51:10 2017
New Revision: 319008
URL: http://llvm.org/viewvc/llvm-project?rev=319008&view=rev
Log:
[ELF] Do not keep symbols if they referenced only from discarded sections.
This patch also ensures that in case of "--as-needed" is used,
DT_NEEDED entries are not created if they are required only by
these eliminated symbols.
Differential Revision: https://reviews.llvm.org/D38790
Added:
lld/trunk/test/ELF/Inputs/gc-sections-shared2.s
lld/trunk/test/ELF/gc-collect-undefined.s
Modified:
lld/trunk/ELF/MarkLive.cpp
lld/trunk/ELF/SymbolTable.cpp
lld/trunk/ELF/Symbols.h
lld/trunk/ELF/Writer.cpp
lld/trunk/test/ELF/gc-sections-shared.s
Modified: lld/trunk/ELF/MarkLive.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/MarkLive.cpp?rev=319008&r1=319007&r2=319008&view=diff
==============================================================================
--- lld/trunk/ELF/MarkLive.cpp (original)
+++ lld/trunk/ELF/MarkLive.cpp Sun Nov 26 21:51:10 2017
@@ -64,6 +64,12 @@ static void resolveReloc(InputSectionBas
std::function<void(InputSectionBase *, uint64_t)> Fn) {
Symbol &B = Sec.getFile<ELFT>()->getRelocTargetSym(Rel);
+ // If a symbol is referenced in a live section, it is used.
+ B.Used = true;
+ if (auto *SS = dyn_cast<SharedSymbol>(&B))
+ if (!SS->isWeak())
+ SS->getFile<ELFT>()->IsNeeded = true;
+
if (auto *D = dyn_cast<Defined>(&B)) {
if (!D->Section)
return;
Modified: lld/trunk/ELF/SymbolTable.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.cpp?rev=319008&r1=319007&r2=319008&view=diff
==============================================================================
--- lld/trunk/ELF/SymbolTable.cpp (original)
+++ lld/trunk/ELF/SymbolTable.cpp Sun Nov 26 21:51:10 2017
@@ -304,7 +304,8 @@ Symbol *SymbolTable::addUndefined(String
if (!S->isDefined())
S->Binding = Binding;
if (auto *SS = dyn_cast<SharedSymbol>(S))
- SS->getFile<ELFT>()->IsNeeded = true;
+ if (!Config->GcSections)
+ SS->getFile<ELFT>()->IsNeeded = true;
}
if (auto *L = dyn_cast<Lazy>(S)) {
// An undefined weak will not fetch archive members. See comment on Lazy in
@@ -500,7 +501,7 @@ void SymbolTable::addShared(StringRef Na
Sym.st_value, Sym.st_size, Alignment, Verdef);
if (!WasInserted) {
S->Binding = Binding;
- if (!S->isWeak())
+ if (!S->isWeak() && !Config->GcSections)
File->IsNeeded = true;
}
}
Modified: lld/trunk/ELF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=319008&r1=319007&r2=319008&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.h (original)
+++ lld/trunk/ELF/Symbols.h Sun Nov 26 21:51:10 2017
@@ -134,8 +134,8 @@ protected:
uint8_t Type)
: Binding(Binding), SymbolKind(K), NeedsPltAddr(false),
IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
- IsInIgot(false), IsPreemptible(false), Type(Type), StOther(StOther),
- Name(Name) {}
+ IsInIgot(false), IsPreemptible(false), Used(!Config->GcSections),
+ Type(Type), StOther(StOther), Name(Name) {}
const unsigned SymbolKind : 8;
@@ -157,6 +157,9 @@ public:
unsigned IsPreemptible : 1;
+ // True if an undefined or shared symbol is used from a live section.
+ unsigned Used : 1;
+
// The following fields have the same meaning as the ELF symbol attributes.
uint8_t Type; // symbol type
uint8_t StOther; // st_other field value
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=319008&r1=319007&r2=319008&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Sun Nov 26 21:51:10 2017
@@ -448,8 +448,9 @@ static bool includeInSymtab(const Symbol
if (auto *S = dyn_cast<MergeInputSection>(Sec))
if (!S->getSectionPiece(D->Value)->Live)
return false;
+ return true;
}
- return true;
+ return B.Used;
}
// Local symbols are not in the linker's symbol table. This function scans
Added: lld/trunk/test/ELF/Inputs/gc-sections-shared2.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/Inputs/gc-sections-shared2.s?rev=319008&view=auto
==============================================================================
--- lld/trunk/test/ELF/Inputs/gc-sections-shared2.s (added)
+++ lld/trunk/test/ELF/Inputs/gc-sections-shared2.s Sun Nov 26 21:51:10 2017
@@ -0,0 +1,3 @@
+.global qux
+.type qux, @function
+qux:
Added: lld/trunk/test/ELF/gc-collect-undefined.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/gc-collect-undefined.s?rev=319008&view=auto
==============================================================================
--- lld/trunk/test/ELF/gc-collect-undefined.s (added)
+++ lld/trunk/test/ELF/gc-collect-undefined.s Sun Nov 26 21:51:10 2017
@@ -0,0 +1,19 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %tout --gc-sections -shared
+# RUN: llvm-nm -D %tout | FileCheck %s
+
+# CHECK-NOT: qux
+# CHECK: bar
+# CHECK-NOT: qux
+
+ .global foo,bar,qux
+ .local baz
+
+ .section .data.foo,"aw",%progbits
+foo:
+ .dc.a bar
+
+ .section .bata.baz,"aw",%progbits
+baz:
+ .dc.a qux
Modified: lld/trunk/test/ELF/gc-sections-shared.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/gc-sections-shared.s?rev=319008&r1=319007&r2=319008&view=diff
==============================================================================
--- lld/trunk/test/ELF/gc-sections-shared.s (original)
+++ lld/trunk/test/ELF/gc-sections-shared.s Sun Nov 26 21:51:10 2017
@@ -1,14 +1,18 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/shared.s -o %t2.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/gc-sections-shared.s -o %t3.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/gc-sections-shared2.s -o %t4.o
# RUN: ld.lld -shared %t2.o -o %t2.so
# RUN: ld.lld -shared %t3.o -o %t3.so
+# RUN: ld.lld -shared %t4.o -o %t4.so
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
-# RUN: ld.lld --gc-sections --export-dynamic-symbol foo -o %t %t.o --as-needed %t2.so %t3.so
+# RUN: ld.lld --gc-sections --export-dynamic-symbol foo -o %t %t.o --as-needed %t2.so %t3.so %t4.so
# RUN: llvm-readobj --dynamic-table --dyn-symbols %t | FileCheck %s
# This test the property that we have a needed line for every undefined.
-# It would also be OK to drop bar2 and the need for the .so
+# It would also be OK to keep bar2 and the need for %t2.so
+# At the same time, weak symbols should not cause adding DT_NEEDED;
+# this case is checked with symbol qux and %t4.so.
# CHECK: DynamicSymbols [
# CHECK-NEXT: Symbol {
@@ -21,16 +25,16 @@
# CHECK-NEXT: Section: Undefined (0x0)
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
-# CHECK-NEXT: Name: bar2
+# CHECK-NEXT: Name: bar
# CHECK-NEXT: Value:
# CHECK-NEXT: Size:
# CHECK-NEXT: Binding: Global
# CHECK-NEXT: Type:
# CHECK-NEXT: Other:
-# CHECK-NEXT: Section: Undefined
+# CHECK-NEXT: Section: .text
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
-# CHECK-NEXT: Name: bar
+# CHECK-NEXT: Name: foo
# CHECK-NEXT: Value:
# CHECK-NEXT: Size:
# CHECK-NEXT: Binding: Global
@@ -39,13 +43,13 @@
# CHECK-NEXT: Section: .text
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
-# CHECK-NEXT: Name: foo
+# CHECK-NEXT: Name: qux
# CHECK-NEXT: Value:
# CHECK-NEXT: Size:
-# CHECK-NEXT: Binding: Global
+# CHECK-NEXT: Binding: Weak
# CHECK-NEXT: Type:
# CHECK-NEXT: Other:
-# CHECK-NEXT: Section: .text
+# CHECK-NEXT: Section: Undefined
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: baz
@@ -59,7 +63,6 @@
# CHECK-NEXT: ]
# CHECK-NOT: NEEDED
-# CHECK: NEEDED Shared library: [{{.*}}2.so]
# CHECK: NEEDED Shared library: [{{.*}}3.so]
# CHECK-NOT: NEEDED
@@ -75,8 +78,10 @@ ret
.section .text._start, "ax"
.globl _start
+.weak qux
_start:
call baz
+call qux
ret
.section .text.unused, "ax"
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