[lld] Allow rel iplt symbols with dynamic symbol table

[smeenai]

Summary

Emit these symbols as long as we're building in a static configuration,
even if we're emitting a dynamic symbol table. This is consistent with
both bfd and gold.

Ordinarily, the combination of -static and -export-dynamic wouldn't make
much sense. Unfortunately, cmake versions prior to 3.4 forcefully
injected -rdynamic [1], so it seems worthwhile to support.

[1] https://cmake.org/cmake/help/v3.4/policy/CMP0065.html

[smeenai]

Instead of duplicating the test, I can either generalize the existing test to handle both the regular and --export-dynamic cases by replacing hardcoded values with regular expressions where necessary, or just add multiple check prefixes to the existing test and handle the value differences that way. Let me know what's preferable.

[ruiu]

I'd just check for the existence of __rela_iplt_{start,end} symbols. We don't need to verify its disassembly as that should already been tested by other tests.

[smeenai]

Simplify test

[ruiu]

test/ELF/gnu-ifunc-dynsym.s

8

Remove -DAG?

[smeenai]

Address comment

[smeenai]

test/ELF/gnu-ifunc-dynsym.s

8

I had the -DAG because I don't care about the order in which the symbols appear, only that they're both present. I'm happy without it as well though.

[smeenai]

test/ELF/gnu-ifunc-dynsym.s

8

To clarify, I meant their order in the llvm-nm output. Of course the end symbol should be after the start symbol in terms of addresses, but llvm-nm appears to print out symbols in reverse order of addresses, at least in this instance.

[ruiu]

LGTM

test/ELF/gnu-ifunc-dynsym.s

8

Ah, I didn't actually know that FileCheck had such feature.

ELF/Writer.cpp

 
 // The beginning and the ending of .rel[a].plt section are marked
 // with __rel[a]_iplt_{start,end} symbols if it is a statically linked
 // executable. The runtime needs these symbols in order to resolve
 // all IRELATIVE relocs on startup. For dynamic executables, we don't
 // need these symbols, since IRELATIVE relocs are resolved through GOT
 // and PLT. For details, see http://www.airs.com/blog/archives/403.
 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
-  if (InX::DynSymTab)
+  if (!Config->Static)
     return;
   StringRef S = Config->IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
   addOptionalRegular<ELFT>(S, In<ELFT>::RelaIplt, 0, STV_HIDDEN, STB_WEAK);
 
   S = Config->IsRela ? "__rela_iplt_end" : "__rel_iplt_end";
   addOptionalRegular<ELFT>(S, In<ELFT>::RelaIplt, -1, STV_HIDDEN, STB_WEAK);
 }
 

test/ELF/gnu-ifunc-dynsym.s

+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+// RUN: ld.lld -static -export-dynamic %t.o -o %tout
+// RUN: llvm-objdump -d %tout | FileCheck %s --check-prefix=DISASM
+// RUN: llvm-readobj -r -symbols -sections %tout | FileCheck %s
+// REQUIRES: x86
+
+// CHECK:      Sections [
+// CHECK:       Section {
+// CHECK:       Index: 1
+// CHECK-NEXT:  Name: .dynsym
+// CHECK-NEXT:  Type: SHT_DYNSYM
+// CHECK-NEXT:  Flags [
+// CHECK-NEXT:    SHF_ALLOC
+// CHECK-NEXT:  ]
+// CHECK-NEXT:  Address: 0x2001C8
+// CHECK-NEXT:  Offset: 0x1C8
+// CHECK-NEXT:  Size: 96
+// CHECK-NEXT:  Link: 3
+// CHECK-NEXT:  Info: 1
+// CHECK-NEXT:  AddressAlignment: 8
+// CHECK-NEXT:  EntrySize: 24
+// CHECK-NEXT:  }
+// CHECK:       Section {
+// CHECK:       Index: 4
+// CHECK-NEXT:  Name: .rela.plt
+// CHECK-NEXT:  Type: SHT_RELA
+// CHECK-NEXT:  Flags [
+// CHECK-NEXT:    SHF_ALLOC
+// CHECK-NEXT:  ]
+// CHECK-NEXT:  Address: [[RELA:.*]]
+// CHECK-NEXT:  Offset: 0x260
+// CHECK-NEXT:  Size: 48
+// CHECK-NEXT:  Link: 1
+// CHECK-NEXT:  Info: 0
+// CHECK-NEXT:  AddressAlignment: 8
+// CHECK-NEXT:  EntrySize: 24
+// CHECK-NEXT: }
+// CHECK:      Relocations [
+// CHECK-NEXT:   Section ({{.*}}) .rela.plt {
+// CHECK-NEXT:     0x202000 R_X86_64_IRELATIVE
+// CHECK-NEXT:     0x202008 R_X86_64_IRELATIVE
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+// CHECK:      Symbols [
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name:
+// CHECK-NEXT:    Value: 0x0
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local
+// CHECK-NEXT:    Type: None
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: Undefined
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: __rela_iplt_end
+// CHECK-NEXT:    Value: 0x200290
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local
+// CHECK-NEXT:    Type: None
+// CHECK-NEXT:    Other [
+// CHECK-NEXT:      STV_HIDDEN
+// CHECK-NEXT:    ]
+// CHECK-NEXT:    Section: .rela.plt
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: __rela_iplt_start
+// CHECK-NEXT:    Value: [[RELA]]
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local
+// CHECK-NEXT:    Type: None
+// CHECK-NEXT:    Other [
+// CHECK-NEXT:      STV_HIDDEN
+// CHECK-NEXT:    ]
+// CHECK-NEXT:    Section: .rela.plt
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: _DYNAMIC (50)
+// CHECK-NEXT:    Value: 0x203000
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Local (0x0)
+// CHECK-NEXT:    Type: None (0x0)
+// CHECK-NEXT:    Other [ (0x2)
+// CHECK-NEXT:      STV_HIDDEN (0x2)
+// CHECK-NEXT:    ]
+// CHECK-NEXT:    Section: .dynamic (0x8)
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: _start
+// CHECK-NEXT:    Value: 0x201002
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Global
+// CHECK-NEXT:    Type: None
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: bar
+// CHECK-NEXT:    Value: 0x201001
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Global
+// CHECK-NEXT:    Type: GNU_IFunc
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text
+// CHECK-NEXT:  }
+// CHECK-NEXT:  Symbol {
+// CHECK-NEXT:    Name: foo
+// CHECK-NEXT:    Value: 0x201000
+// CHECK-NEXT:    Size: 0
+// CHECK-NEXT:    Binding: Global
+// CHECK-NEXT:    Type: GNU_IFunc
+// CHECK-NEXT:    Other: 0
+// CHECK-NEXT:    Section: .text
+// CHECK-NEXT:  }
+// CHECK-NEXT: ]
+
+// DISASM: Disassembly of section .text:
+// DISASM-NEXT: foo:
+// DISASM-NEXT:  201000: {{.*}} retq
+// DISASM:      bar:
+// DISASM-NEXT:  201001: {{.*}} retq
+// DISASM:      _start:
+// DISASM-NEXT:  201002: {{.*}} callq 25
+// DISASM-NEXT:  201007: {{.*}} callq 36
+// DISASM-NEXT:  20100c: {{.*}} movl $2097760, %edx
+// DISASM-NEXT:  201011: {{.*}} movl $2097808, %edx
+// DISASM-NEXT:  201016: {{.*}} movl $2097809, %edx
+// DISASM-NEXT: Disassembly of section .plt:
+// DISASM-NEXT: .plt:
+// DISASM-NEXT:  201020: {{.*}} jmpq *4058(%rip)
+// DISASM-NEXT:  201026: {{.*}} pushq $0
+// DISASM-NEXT:  20102b: {{.*}} jmp -32 <_start+0xE>
+// DISASM-NEXT:  201030: {{.*}} jmpq *4050(%rip)
+// DISASM-NEXT:  201036: {{.*}} pushq $1
+// DISASM-NEXT:  20103b: {{.*}} jmp -48 <_start+0xE>
+
+.text
+.type foo STT_GNU_IFUNC
+.globl foo
+foo:
+ ret
+
+.type bar STT_GNU_IFUNC
+.globl bar
+bar:
+ ret
+
+.globl _start
+_start:
+ call foo
+ call bar
+ movl $__rela_iplt_start,%edx
+ movl $__rela_iplt_end,%edx
+ movl $__rela_iplt_end + 1,%edx