Index: ELF/InputFiles.h =================================================================== --- ELF/InputFiles.h +++ ELF/InputFiles.h @@ -179,6 +179,7 @@ private: void initializeSections(llvm::DenseSet &ComdatGroups); void initializeSymbols(); + void initializeReverseDependencies(); InputSectionBase *getRelocTarget(const Elf_Shdr &Sec); InputSectionBase *createInputSection(const Elf_Shdr &Sec); Index: ELF/InputFiles.cpp =================================================================== --- ELF/InputFiles.cpp +++ ELF/InputFiles.cpp @@ -145,6 +145,8 @@ // Read section and symbol tables. initializeSections(ComdatGroups); initializeSymbols(); + if (Config->GcSections && Config->EMachine == EM_ARM ) + initializeReverseDependencies(); } // Sections with SHT_GROUP and comdat bits define comdat section groups. @@ -261,6 +263,25 @@ } } +// .ARM.exidx sections have a reverse dependency on the InputSection they +// have a SHF_LINK_ORDER dependency, this is identified by the sh_link. +template +void elf::ObjectFile::initializeReverseDependencies() { + unsigned I = -1; + for (const Elf_Shdr &Sec : this->ELFObj.sections()) { + ++I; + if (Sections[I] == &InputSection::Discarded) + continue; + if (Sec.sh_flags & SHF_LINK_ORDER) { + if (Sec.sh_link >= Sections.size()) + fatal(getFilename(this) + ": invalid sh_link index: " + + Twine(Sec.sh_link)); + auto *IS = dyn_cast>(Sections[Sec.sh_link]); + IS->DependentSection = Sections[I]; + } + } +} + template InputSectionBase * elf::ObjectFile::getRelocTarget(const Elf_Shdr &Sec) { Index: ELF/InputSection.h =================================================================== --- ELF/InputSection.h +++ ELF/InputSection.h @@ -228,6 +228,9 @@ // to. The writer sets a value. uint64_t OutSecOff = 0; + // InputSection that is dependent on us (reverse dependency for GC) + InputSectionBase *DependentSection = nullptr; + static bool classof(const InputSectionBase *S); InputSectionBase *getRelocatedSection(); Index: ELF/MarkLive.cpp =================================================================== --- ELF/MarkLive.cpp +++ ELF/MarkLive.cpp @@ -91,6 +91,8 @@ Fn(resolveReloc(Sec, Rel)); } } + if (Sec.DependentSection) + Fn({Sec.DependentSection, 0}); } // The .eh_frame section is an unfortunate special case. Index: test/ELF/arm-exidx-gc.s =================================================================== --- /dev/null +++ test/ELF/arm-exidx-gc.s @@ -0,0 +1,123 @@ +// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t +// RUN: ld.lld %t -o %t2 --gc-sections 2>&1 +// RUN: llvm-objdump -d -triple=armv7a-none-linux-gnueabi %t2 | FileCheck %s +// RUN: llvm-objdump -s -triple=armv7a-none-linux-gnueabi %t2 | FileCheck -check-prefix=CHECK-EXIDX %s +// REQUIRES: arm + +// Test the behavior of .ARM.exidx sections under garbage collection +// A .ARM.exidx section is live if it has a relocation to a live executable +// section. +// A .ARM.exidx section may have a relocation to a .ARM.extab section, if the +// .ARM.exidx is live then the .ARM.extab section is live + + .syntax unified + .section .text.func1, "ax",%progbits + .global func1 +func1: + .fnstart + bx lr + .save {r7, lr} + .setfp r7, sp, #0 + .fnend + + .section .text.unusedfunc1, "ax",%progbits + .global unusedfunc1 +unusedfunc1: + .fnstart + bx lr + .cantunwind + .fnend + + // Unwinding instructions for .text2 too large for an inline entry ARM.exidx + // entry. A separate .ARM.extab section is created to hold the unwind entries + // The .ARM.exidx table entry has a reference to the .ARM.extab section. + .section .text.func2, "ax",%progbits + .global func2 +func2: + .fnstart + bx lr + .personality __gxx_personality_v0 + .handlerdata + .section .text.func2 + .fnend + + // An unused function with a reference to a .ARM.extab section. Both should + // be removed by gc. + .section .text.unusedfunc2, "ax",%progbits + .global unusedfunc2 +unusedfunc2: + .fnstart + bx lr + .personality __gxx_personality_v1 + .handlerdata + .section .text.unusedfunc2 + .fnend + + // Dummy implementation of personality routines to satisfy reference from + // exception tables + .section .text.__gcc_personality_v0, "ax", %progbits + .global __gxx_personality_v0 +__gxx_personality_v0: + .fnstart + bx lr + .cantunwind + .fnend + + .section .text.__gcc_personality_v1, "ax", %progbits + .global __gxx_personality_v1 +__gxx_personality_v1: + .fnstart + bx lr + .cantunwind + .fnend + + .section .text.__aeabi_unwind_cpp_pr0, "ax", %progbits + .global __aeabi_unwind_cpp_pr0 +__aeabi_unwind_cpp_pr0: + .fnstart + bx lr + .cantunwind + .fnend + +// Entry point for GC + .text + .global _start +_start: + bl func1 + bl func2 + bx lr + +// GC should have only removed unusedfunc1 and unusedfunc2 the personality +// routines are kept alive by references from live .ARM.exidx and .ARM.extab +// sections +// CHECK: Disassembly of section .text: +// CHECK-NEXT: _start: +// CHECK-NEXT: 11000: 01 00 00 eb bl #4 +// CHECK-NEXT: 11004: 01 00 00 eb bl #4 +// CHECK-NEXT: 11008: 1e ff 2f e1 bx lr +// CHECK: func1: +// CHECK-NEXT: 1100c: 1e ff 2f e1 bx lr +// CHECK: func2: +// CHECK-NEXT: 11010: 1e ff 2f e1 bx lr +// CHECK: __gxx_personality_v0: +// CHECK-NEXT: 11014: 1e ff 2f e1 bx lr +// CHECK: __aeabi_unwind_cpp_pr0: +// CHECK-NEXT: 11018: 1e ff 2f e1 bx lr + +// GC should have removed table entries for unusedfunc1, unusedfunc2 +// and __gxx_personality_v1 +// CHECK-NOT: unusedfunc1 +// CHECK-NOT: unusedfunc2 +// CHECK-NOT: __gxx_personality_v1 + +// CHECK-EXIDX-NOT: Contents of section .ARM.extab.text.unusedfunc2: +// CHECK-EXIDX: Contents of section .ARM.exidx: +// 100d4 + f38 = 1100c = func1 +// 100dc + f34 = 11010 = func2 (100e0 + 14 = 100f4 = .ARM.extab.text.func2) +// CHECK-EXIDX-NEXT: 100d4 380f0000 08849780 340f0000 14000000 +// 100e4 + f30 = 11014 = __gxx_personality_v0 +// 100ec + f2c = 11018 = __aeabi_unwind_cpp_pr0 +// CHECK-EXIDX-NEXT: 100e4 300f0000 01000000 2c0f0000 01000000 +// CHECK-EXIDX-NEXT: Contents of section .ARM.extab.text.func2: +// 100f4 + f20 = 11014 = __gxx_personality_v0 +// CHECK-EXIDX-NEXT: 100f4 200f0000 b0b0b000