From 1d4b3023dc6ada3d82af12716f2a15320efae293 Mon Sep 17 00:00:00 2001 From: Rafael Espindola Date: Tue, 28 Nov 2017 20:17:58 +0000 Subject: [PATCH] Bring back r319008. This includes a fix to mark copy reloc aliases as used. Original message: [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. llvm-svn: 319215 --- lld/ELF/MarkLive.cpp | 6 ++++++ lld/ELF/Relocations.cpp | 1 + lld/ELF/SymbolTable.cpp | 5 +++-- lld/ELF/Symbols.h | 7 +++++-- lld/ELF/Writer.cpp | 3 ++- lld/test/ELF/Inputs/gc-sections-shared2.s | 3 +++ lld/test/ELF/gc-collect-undefined.s | 19 +++++++++++++++++++ lld/test/ELF/gc-sections-shared.s | 23 ++++++++++++++--------- 8 files changed, 53 insertions(+), 14 deletions(-) create mode 100644 lld/test/ELF/Inputs/gc-sections-shared2.s create mode 100644 lld/test/ELF/gc-collect-undefined.s diff --git a/lld/ELF/MarkLive.cpp b/lld/ELF/MarkLive.cpp index 3520abe..e619a95 100644 --- a/lld/ELF/MarkLive.cpp +++ b/lld/ELF/MarkLive.cpp @@ -64,6 +64,12 @@ static void resolveReloc(InputSectionBase &Sec, RelT &Rel, std::function Fn) { Symbol &B = Sec.getFile()->getRelocTargetSym(Rel); + // If a symbol is referenced in a live section, it is used. + B.Used = true; + if (auto *SS = dyn_cast(&B)) + if (!SS->isWeak()) + SS->getFile()->IsNeeded = true; + if (auto *D = dyn_cast(&B)) { if (!D->Section) return; diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp index e5f8266..2ebb58b 100644 --- a/lld/ELF/Relocations.cpp +++ b/lld/ELF/Relocations.cpp @@ -541,6 +541,7 @@ template static void addCopyRelSymbol(SharedSymbol *SS) { Sym->CopyRelSec = Sec; Sym->IsPreemptible = false; Sym->IsUsedInRegularObj = true; + Sym->Used = true; } In::RelaDyn->addReloc({Target->CopyRel, Sec, 0, false, SS, 0}); diff --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp index 99f41f8..08a6d2f 100644 --- a/lld/ELF/SymbolTable.cpp +++ b/lld/ELF/SymbolTable.cpp @@ -305,7 +305,8 @@ Symbol *SymbolTable::addUndefined(StringRef Name, uint8_t Binding, S->Binding = Binding; if (Binding != STB_WEAK) { if (auto *SS = dyn_cast(S)) - SS->getFile()->IsNeeded = true; + if (!Config->GcSections) + SS->getFile()->IsNeeded = true; } if (auto *L = dyn_cast(S)) { // An undefined weak will not fetch archive members. See comment on Lazy in @@ -500,7 +501,7 @@ void SymbolTable::addShared(StringRef Name, SharedFile *File, Alignment, Verdef); if (!WasInserted) { S->Binding = Binding; - if (!S->isWeak()) + if (!S->isWeak() && !Config->GcSections) File->IsNeeded = true; } } diff --git a/lld/ELF/Symbols.h b/lld/ELF/Symbols.h index 9e5882a..99fc61b 100644 --- a/lld/ELF/Symbols.h +++ b/lld/ELF/Symbols.h @@ -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 diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp index e74289c..0ab33f5 100644 --- a/lld/ELF/Writer.cpp +++ b/lld/ELF/Writer.cpp @@ -448,8 +448,9 @@ static bool includeInSymtab(const Symbol &B) { if (auto *S = dyn_cast(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 diff --git a/lld/test/ELF/Inputs/gc-sections-shared2.s b/lld/test/ELF/Inputs/gc-sections-shared2.s new file mode 100644 index 0000000..fb69c0e --- /dev/null +++ b/lld/test/ELF/Inputs/gc-sections-shared2.s @@ -0,0 +1,3 @@ +.global qux +.type qux, @function +qux: diff --git a/lld/test/ELF/gc-collect-undefined.s b/lld/test/ELF/gc-collect-undefined.s new file mode 100644 index 0000000..7ade554 --- /dev/null +++ b/lld/test/ELF/gc-collect-undefined.s @@ -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 diff --git a/lld/test/ELF/gc-sections-shared.s b/lld/test/ELF/gc-sections-shared.s index 80b3d61..b9ce5de 100644 --- a/lld/test/ELF/gc-sections-shared.s +++ b/lld/test/ELF/gc-sections-shared.s @@ -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" -- 2.7.4