[lld] r328624 - [ELF] Disable ICF for synthetic sections

[Rafael Avila de Espindola via llvm-commits]

Thanks!
Andrew Ng via llvm-commits <llvm-commits at lists.llvm.org> writes:

> Author: anng
> Date: Tue Mar 27 07:10:07 2018
> New Revision: 328624
>
> URL: http://llvm.org/viewvc/llvm-project?rev=328624&view=rev
> Log:
> [ELF] Disable ICF for synthetic sections
>
> The Data member of synthetic section's is not valid and empty. The Data
> member is required to be valid by ICF as it is used by ICF to determine
> the equality of section contents. Therefore, exclude synthetic sections
> from ICF.
>
> Fixes bug PR36910.
>
> Differential Revision: https://reviews.llvm.org/D44923
>
> Modified:
>     lld/trunk/ELF/ICF.cpp
>     lld/trunk/test/ELF/icf-merged-sections.s
>
> Modified: lld/trunk/ELF/ICF.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/ICF.cpp?rev=328624&r1=328623&r2=328624&view=diff
> ==============================================================================
> --- lld/trunk/ELF/ICF.cpp (original)
> +++ lld/trunk/ELF/ICF.cpp Tue Mar 27 07:10:07 2018
> @@ -77,6 +77,7 @@
>  #include "Config.h"
>  #include "SymbolTable.h"
>  #include "Symbols.h"
> +#include "SyntheticSections.h"
>  #include "lld/Common/Threads.h"
>  #include "llvm/ADT/Hashing.h"
>  #include "llvm/BinaryFormat/ELF.h"
> @@ -166,6 +167,12 @@ static bool isEligible(InputSection *S)
>    if (!(S->Flags & SHF_EXECINSTR) && !Config->IgnoreDataAddressEquality)
>      return false;
>  
> +  // Don't merge synthetic sections as their Data member is not valid and empty.
> +  // The Data member needs to be valid for ICF as it is used by ICF to determine
> +  // the equality of section contents.
> +  if (isa<SyntheticSection>(S))
> +    return false;
> +
>    // .init and .fini contains instructions that must be executed to
>    // initialize and finalize the process. They cannot and should not
>    // be merged.
>
> Modified: lld/trunk/test/ELF/icf-merged-sections.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/icf-merged-sections.s?rev=328624&r1=328623&r2=328624&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/icf-merged-sections.s (original)
> +++ lld/trunk/test/ELF/icf-merged-sections.s Tue Mar 27 07:10:07 2018
> @@ -1,20 +1,28 @@
>  # REQUIRES: x86
>  
>  # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> -# RUN: ld.lld %t.o -o %t --icf=all --ignore-data-address-equality --print-icf-sections | FileCheck %s --check-prefix ICF
> -# RUN: llvm-objdump -s -d -print-imm-hex %t | FileCheck %s
> +# RUN: ld.lld %t.o -o %t --icf=all --ignore-data-address-equality --print-icf-sections | FileCheck -allow-empty --check-prefix=NOICF %s
> +# RUN: llvm-readobj -s -section-data %t | FileCheck %s
>  
> -# ICF: selected section <internal>:(.rodata)
> -# ICF-NEXT: removing identical section <internal>:(.rodata)
> +# Check that merge synthetic sections are not merged by ICF.
>  
> -# CHECK: {{^}}.text:
> -# CHECK-NEXT: movq 0x[[ADDR:[0-9a-f]+]], %rax
> -# CHECK-NEXT: movq 0x[[ADDR]], %rax
> -# CHECK: Contents of section .rodata:
> -# CHECK-NEXT: 2a000000 00000000 67452301 10325476
> +# NOICF-NOT: selected section <internal>:(.rodata)
>  
> -.section .rodata, "a"
> -  .quad 42
> +# CHECK:      Name: .rodata
> +# CHECK-NEXT: Type: SHT_PROGBITS
> +# CHECK-NEXT: Flags [
> +# CHECK-NEXT:   SHF_ALLOC
> +# CHECK-NEXT:   SHF_MERGE
> +# CHECK-NEXT: ]
> +# CHECK-NEXT: Address:
> +# CHECK-NEXT: Offset:
> +# CHECK-NEXT: Size: 16
> +# CHECK-NEXT: Link:
> +# CHECK-NEXT: Info:
> +# CHECK-NEXT: AddressAlignment: 8
> +# CHECK-NEXT: EntrySize: 0
> +# CHECK-NEXT: SectionData (
> +# CHECK-NEXT:   0000: 67452301 10325476 67452301 10325476
>  
>  .section .rodata.cst4,"aM", at progbits,4
>  rodata4:
> @@ -27,7 +35,3 @@ rodata4:
>  rodata8:
>    .long 0x01234567
>    .long 0x76543210
> -
> -.section .text,"ax"
> -  movq rodata4, %rax
> -  movq rodata8, %rax
>
>
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