From 997f2a56dea16a8b0a8827ca00cbaa21fbcd2338 Mon Sep 17 00:00:00 2001 From: Shoaib Meenai Date: Tue, 1 Feb 2022 23:59:50 -0800 Subject: [PATCH] [ELF] Avoid wrapping unreferenced lazy symbols There's a couple of motivations here: * LLD 12 (which I was originally testing with) was adding an undefined symbol to the symbol table if you attempted to wrap an unreferenced lazy symbol, which would later break `--no-allow-shlib-undefined`. LLD on main actually produces a weak undefined symbol, so this doesn't break anyway, but it's cleaner to not have the weak undefined symbol as well. The new behavior also matches bfd and gold. * PROVIDE in a linker script referencing a wrapped symbol would think that an otherwise-unreferenced lazy symbol which was wrapped was actually referenced, and therefore proceed with the definition, which goes against expectations. The new behavior also matches bfd and gold. Reviewed By: MaskRay Differential Revision: https://reviews.llvm.org/D118756 --- lld/ELF/Driver.cpp | 6 ++++- lld/test/ELF/wrap-lazy.test | 58 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 63 insertions(+), 1 deletion(-) create mode 100644 lld/test/ELF/wrap-lazy.test diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp index 406571e..f32f952 100644 --- a/lld/ELF/Driver.cpp +++ b/lld/ELF/Driver.cpp @@ -2047,7 +2047,11 @@ static std::vector addWrappedSymbols(opt::InputArgList &args) { continue; Symbol *sym = symtab->find(name); - if (!sym) + // Avoid wrapping symbols that are lazy and unreferenced at this point, to + // not create undefined references. The isUsedInRegularObj check handles the + // case of a weak reference, which we still want to wrap even though it + // doesn't cause lazy symbols to be extracted. + if (!sym || (sym->isLazy() && !sym->isUsedInRegularObj)) continue; Symbol *real = addUnusedUndefined(saver().save("__real_" + name)); diff --git a/lld/test/ELF/wrap-lazy.test b/lld/test/ELF/wrap-lazy.test new file mode 100644 index 0000000..8b85535 --- /dev/null +++ b/lld/test/ELF/wrap-lazy.test @@ -0,0 +1,58 @@ +# REQUIRES: x86 + +# RUN: split-file %s %t +# RUN: llvm-as %t/lazy.ll -o %tlazybitcode.o +# RUN: llvm-mc -filetype=obj -triple=x86_64-elf %t/dummy.s -o %tdummy.o +# RUN: llvm-mc -filetype=obj -triple=x86_64-elf %t/lazy.s -o %tlazy.o +# RUN: llvm-mc -filetype=obj -triple=x86_64-elf %t/ref.s -o %tref.o +# RUN: llvm-mc -filetype=obj -triple=x86_64-elf %t/weakref.s -o %tweakref.o +# RUN: ld.lld -shared -o %t1.so %tdummy.o --start-lib %tlazy.o --wrap lazy +# RUN: llvm-readelf -s %t1.so | FileCheck --check-prefix=NO-LAZY %s +# RUN: ld.lld -shared -o %t2.so %tdummy.o --start-lib %tlazybitcode.o --wrap lazy +# RUN: llvm-readelf -s %t2.so | FileCheck --check-prefix=NO-LAZY %s +# RUN: ld.lld -shared -o %t3.so %tdummy.o --start-lib %tlazy.o -u lazy --wrap lazy +# RUN: llvm-readelf -s %t3.so | FileCheck --check-prefix=LAZY-DEF %s +# RUN: ld.lld -shared -o %t4.so %tdummy.o %tlazy.o --wrap lazy +# RUN: llvm-readelf -s %t4.so | FileCheck --check-prefix=LAZY-DEF %s +# RUN: ld.lld -shared -o %t5.so %tref.o --start-lib %tlazy.o --wrap lazy +# RUN: llvm-readelf -s %t5.so | FileCheck --check-prefix=LAZY-DEF %s +# RUN: ld.lld -shared -o %t6.so %tweakref.o --start-lib %tlazy.o --wrap lazy +# RUN: llvm-readelf -s %t6.so | FileCheck --check-prefix=LAZY-REF %s +# RUN: ld.lld -shared -o %t7.so %tweakref.o --start-lib %tlazybitcode.o --wrap lazy +# RUN: llvm-readelf -s %t7.so | FileCheck --check-prefix=LAZY-REF %s +# RUN: ld.lld -shared -o %tweakref.so %tweakref.o -soname libweakref.so +# RUN: ld.lld -shared -o %t8.so %tdummy.o %tweakref.so --start-lib %tlazy.o --wrap lazy +# RUN: llvm-readelf -s %t8.so | FileCheck --check-prefix=NO-LAZY %s + +# NO-LAZY-NOT: lazy +# NO-LAZY-NOT: __wrap_lazy + +# LAZY-DEF-DAG: [[#]] lazy +# LAZY-DEF-DAG: UND __wrap_lazy + +# LAZY-REF-DAG: UND lazy +# LAZY-REF-DAG: UND __wrap_lazy + +#--- dummy.s +.globl dummy +dummy: + retq + +#--- lazy.ll +target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-elf" +define void @lazy() { + ret void +} + +#--- lazy.s +.globl lazy +lazy: + retq + +#--- ref.s + jmp lazy + +#--- weakref.s +.weak lazy + jmp lazy -- 2.7.4