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[ELF] Don't special case weak symbols for pie with no shared objects 

D59275 added the following clause to Symbol::includeInDynsym()

  if (isUndefWeak() && Config->Pie && SharedFiles.empty())
    return false;

D59549 explored the possibility to generalize it for -no-pie.

GNU ld's rules are architecture dependent and partly controlled by -z
{,no-}dynamic-undefined-weak. Our attempts to mimic its rules are
actually half-baked and don't provide perceivable benefits (it can save
a few more weak undefined symbols in .dynsym in a -static-pie
executable). Let's just delete the rule for simplicity. We will expect
cosmetic inconsistencies with ld.bfd in certain -static-pie scenarios.

This permits a simplification in D71795.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D71794
This commit is contained in:
Fangrui Song 2019-12-20 21:43:46 -08:00
parent 46e2f89364
commit 96e2376d02
3 changed files with 7 additions and 40 deletions
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5
lld/ELF/Symbols.cpp
View File

@ -278,11 +278,6 @@ bool Symbol::includeInDynsym() const {
if (computeBinding() == STB_LOCAL)
return false;
// If a PIE binary was not linked against any shared libraries, then we can
// safely drop weak undef symbols from .dynsym.
if (isUndefWeak() && config->pie && sharedFiles.empty())
return false;
return isUndefined() || isShared() || exportDynamic || inDynamicList;
}

14
lld/test/ELF/ppc32-weak-undef-call.s
View File

@ -1,19 +1,19 @@
# REQUIRES: ppc
# RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
# RUN: ld.lld %t.o -o %t
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=EXE %s
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=PDE %s
# RUN: ld.lld -pie %t.o -o %t
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=EXE %s
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=PIC %s
# RUN: ld.lld -shared %t.o -o %t
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=SHARED %s
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefix=PIC %s
## It does not really matter how we fixup it, but we cannot overflow and
## should not generate a call stub (this would waste space).
# EXE: bl .+0
# PDE: bl .+0
## With -shared, create a call stub. ld.bfd produces bl .+0
# SHARED: bl .+4
# SHARED: 00000000.plt_pic32.foo:
## With -pie or -shared, create a call stub. ld.bfd produces bl .+0
# PIC: bl .+4
# PIC: 00000000.plt_pic32.foo:
.weak foo
bl foo

28
lld/test/ELF/weak-undef-no-shared-libs.s
View File

@ -1,28 +0,0 @@
// REQUIRES: x86
// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
// RUN: ld.lld -pie %t.o -o %t
// RUN: llvm-readobj -V --dyn-syms %t | FileCheck %s
.globl _start
_start:
.type foo,@function
.weak foo
.long foo@gotpcrel
// Test that an entry for weak undefined symbols is NOT emitted in .dynsym as
// the PIE was not linked with any shared libraries. There are other tests which
// ensure that the weak undefined symbols do get emitted in .dynsym for PIEs
// linked against dynamic libraries.
// CHECK: DynamicSymbols [
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name:
// CHECK-NEXT: Value: 0x0
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Binding: Local (0x0)
// CHECK-NEXT: Type: None (0x0)
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: Undefined (0x0)
// CHECK-NEXT: }
// CHECK-NEXT: ]