[PATCH] D30843: ELF: Resolve _end symbols correctly.

[Rafael Avila de Espindola via llvm-commits]

LGTM

Peter Collingbourne via Phabricator <reviews at reviews.llvm.org> writes:

> pcc created this revision.
>
> Fix a bug introduced in r297313 which caused them to resolve to the end
> of the ELF header in PIEs and DSOs.
>
>
> https://reviews.llvm.org/D30843
>
> Files:
>   lld/ELF/Writer.cpp
>   lld/test/ELF/pre_init_fini_array_missing.s
>
>
> Index: lld/test/ELF/pre_init_fini_array_missing.s
> ===================================================================
> --- lld/test/ELF/pre_init_fini_array_missing.s
> +++ lld/test/ELF/pre_init_fini_array_missing.s
> @@ -1,6 +1,8 @@
>  // RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
>  // RUN: ld.lld %t -o %t2
>  // RUN: llvm-objdump -d %t2 | FileCheck %s
> +// RUN: ld.lld -pie %t -o %t3
> +// RUN: llvm-objdump -d %t3 | FileCheck --check-prefix=PIE %s
>  // REQUIRES: x86
>  
>  .globl _start
> @@ -28,3 +30,14 @@
>  // CHECK-NEXT:   20100f:    e8 ec ef df ff     callq    -2101268
>  // CHECK-NEXT:   201014:    e8 e7 ef df ff     callq    -2101273
>  // CHECK-NEXT:   201019:    e8 e2 ef df ff     callq    -2101278
> +
> +// In position-independent binaries, they resolve to the image base.
> +
> +// PIE:      Disassembly of section .text:
> +// PIE-NEXT: _start:
> +// PIE-NEXT:     1000:	e8 fb ef ff ff 	callq	-4101
> +// PIE-NEXT:     1005:	e8 f6 ef ff ff 	callq	-4106
> +// PIE-NEXT:     100a:	e8 f1 ef ff ff 	callq	-4111
> +// PIE-NEXT:     100f:	e8 ec ef ff ff 	callq	-4116
> +// PIE-NEXT:     1014:	e8 e7 ef ff ff 	callq	-4121
> +// PIE-NEXT:     1019:	e8 e2 ef ff ff 	callq	-4126
> Index: lld/ELF/Writer.cpp
> ===================================================================
> --- lld/ELF/Writer.cpp
> +++ lld/ELF/Writer.cpp
> @@ -1203,10 +1203,15 @@
>    auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
>      // These symbols resolve to the image base if the section does not exist.
>      // A special value -1 indicates end of the section.
> -    if (!OS && Config->pic())
> -      OS = Out::ElfHeader;
> -    addOptionalRegular<ELFT>(Start, OS, 0);
> -    addOptionalRegular<ELFT>(End, OS, OS ? -1 : 0);
> +    if (OS) {
> +      addOptionalRegular<ELFT>(Start, OS, 0);
> +      addOptionalRegular<ELFT>(End, OS, -1);
> +    } else {
> +      if (Config->pic())
> +        OS = Out::ElfHeader;
> +      addOptionalRegular<ELFT>(Start, OS, 0);
> +      addOptionalRegular<ELFT>(End, OS, 0);
> +    }
>    };
>  
>    Define("__preinit_array_start", "__preinit_array_end", Out::PreinitArray);
>
>
> Index: lld/test/ELF/pre_init_fini_array_missing.s
> ===================================================================
> --- lld/test/ELF/pre_init_fini_array_missing.s
> +++ lld/test/ELF/pre_init_fini_array_missing.s
> @@ -1,6 +1,8 @@
>  // RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
>  // RUN: ld.lld %t -o %t2
>  // RUN: llvm-objdump -d %t2 | FileCheck %s
> +// RUN: ld.lld -pie %t -o %t3
> +// RUN: llvm-objdump -d %t3 | FileCheck --check-prefix=PIE %s
>  // REQUIRES: x86
>  
>  .globl _start
> @@ -28,3 +30,14 @@
>  // CHECK-NEXT:   20100f:    e8 ec ef df ff     callq    -2101268
>  // CHECK-NEXT:   201014:    e8 e7 ef df ff     callq    -2101273
>  // CHECK-NEXT:   201019:    e8 e2 ef df ff     callq    -2101278
> +
> +// In position-independent binaries, they resolve to the image base.
> +
> +// PIE:      Disassembly of section .text:
> +// PIE-NEXT: _start:
> +// PIE-NEXT:     1000:	e8 fb ef ff ff 	callq	-4101
> +// PIE-NEXT:     1005:	e8 f6 ef ff ff 	callq	-4106
> +// PIE-NEXT:     100a:	e8 f1 ef ff ff 	callq	-4111
> +// PIE-NEXT:     100f:	e8 ec ef ff ff 	callq	-4116
> +// PIE-NEXT:     1014:	e8 e7 ef ff ff 	callq	-4121
> +// PIE-NEXT:     1019:	e8 e2 ef ff ff 	callq	-4126
> Index: lld/ELF/Writer.cpp
> ===================================================================
> --- lld/ELF/Writer.cpp
> +++ lld/ELF/Writer.cpp
> @@ -1203,10 +1203,15 @@
>    auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
>      // These symbols resolve to the image base if the section does not exist.
>      // A special value -1 indicates end of the section.
> -    if (!OS && Config->pic())
> -      OS = Out::ElfHeader;
> -    addOptionalRegular<ELFT>(Start, OS, 0);
> -    addOptionalRegular<ELFT>(End, OS, OS ? -1 : 0);
> +    if (OS) {
> +      addOptionalRegular<ELFT>(Start, OS, 0);
> +      addOptionalRegular<ELFT>(End, OS, -1);
> +    } else {
> +      if (Config->pic())
> +        OS = Out::ElfHeader;
> +      addOptionalRegular<ELFT>(Start, OS, 0);
> +      addOptionalRegular<ELFT>(End, OS, 0);
> +    }
>    };
>  
>    Define("__preinit_array_start", "__preinit_array_end", Out::PreinitArray);