[lld] r296378 - Add terminator to .eh_frame sections

Rafael Avila de Espindola via llvm-commits llvm-commits at lists.llvm.org
Tue Feb 28 10:41:35 PST 2017


I am pretty sure this is wrong. Given

        .cfi_startproc
        nop
        .cfi_endproc

bfd and gold produce a .eh_frame that is 0x30 bytes long. We used to do
that too, but now we produce one that is 0x34.

I think that normally the terminator comes from a .o file that gcc/clang
adds to the link.

Rui, could you revert this for now?

Mark, could you provide an example where bfd/gold is adding the
terminator?

Cheers,
Rafael

Rui Ueyama via llvm-commits <llvm-commits at lists.llvm.org> writes:

> Author: ruiu
> Date: Mon Feb 27 14:44:59 2017
> New Revision: 296378
>
> URL: http://llvm.org/viewvc/llvm-project?rev=296378&view=rev
> Log:
> Add terminator to .eh_frame sections
>
> Patch by Mark Kettenis.
>
> Currenlty ld.lld does not add a terminator (a CIE with its length field
> set to zero) to the .eh_frame sections it generates.  While the relevant
> standards (the AMD64 SysV ABI and the Linux LSB) are not explicit about
> this, such a terminator is expected by some unwinder implementations and
> seems to be always emitted by ld.bfd. In addition to that, the Linux LSB
>
>   https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html#EHFRAME
>
> explicitly says that
>
>   The .eh_frame section shall contain 1 or more Call Frame Information
>   (CFI) records.
>
> Currently, if the .eh_frame sections of the input files only contain
> terminators, ld.lld emits a zero=sized .eh_frame section
> which clearly doesn't meet that requirement.
>
> The diff makes sure a terminator gets added to each .eh_frame section
> and adjusts all the relevant tests to account for that.  An additional
> test isn't needed as these adjustments mean that the existence of the
> terminator is tested for by several tests already.
>
> Differential Revision: https://reviews.llvm.org/D30335
>
> Modified:
>     lld/trunk/ELF/SyntheticSections.cpp
>     lld/trunk/test/ELF/eh-frame-hdr.s
>     lld/trunk/test/ELF/eh-frame-merge.s
>     lld/trunk/test/ELF/ehframe-relocation.s
>     lld/trunk/test/ELF/invalid-fde-rel.s
>     lld/trunk/test/ELF/linkerscript/eh-frame-hdr.s
>     lld/trunk/test/ELF/linkerscript/symbols-synthetic.s
>     lld/trunk/test/ELF/map-file.s
>     lld/trunk/test/ELF/relocatable-eh-frame.s
>
> Modified: lld/trunk/ELF/SyntheticSections.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SyntheticSections.cpp?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/ELF/SyntheticSections.cpp (original)
> +++ lld/trunk/ELF/SyntheticSections.cpp Mon Feb 27 14:44:59 2017
> @@ -540,7 +540,14 @@ template <class ELFT> void EhFrameSectio
>        Off += alignTo(Fde->size(), sizeof(uintX_t));
>      }
>    }
> -  this->Size = Off;
> +
> +  // Add a CIE record of length 0 as a terminator. While the relevant
> +  // standards don't explicitly require such a terminator, ld.bfd and
> +  // ld.gold always seem to add one and some unwiders rely on its
> +  // presence. It also prevents us from generating a .eh_frame section
> +  // with zero Call Frame Information records, which isn't allowed by
> +  // the LSB standard.
> +  this->Size = Off + 4;
>  }
>  
>  template <class ELFT> static uint64_t readFdeAddr(uint8_t *Buf, int Size) {
>
> Modified: lld/trunk/test/ELF/eh-frame-hdr.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/eh-frame-hdr.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/eh-frame-hdr.s (original)
> +++ lld/trunk/test/ELF/eh-frame-hdr.s Mon Feb 27 14:44:59 2017
> @@ -84,7 +84,7 @@ _start:
>  // HDR-NEXT:    ]
>  // HDR-NEXT:    Address: 0x200180
>  // HDR-NEXT:    Offset: 0x180
> -// HDR-NEXT:    Size: 96
> +// HDR-NEXT:    Size: 100
>  // HDR-NEXT:    Link: 0
>  // HDR-NEXT:    Info: 0
>  // HDR-NEXT:    AddressAlignment: 8
> @@ -96,6 +96,7 @@ _start:
>  // HDR-NEXT:      0030: 14000000 34000000 490E0000 01000000
>  // HDR-NEXT:      0040: 00000000 00000000 14000000 4C000000
>  // HDR-NEXT:      0050: 320E0000 01000000 00000000 00000000
> +// HDR-NEXT:      0060: 00000000
>  // HDR-NEXT:    )
>  //            CIE: 14000000 00000000 017A5200 01781001 1B0C0708 90010000
>  //            FDE(1): 14000000 1C000000 600E0000 01000000 00000000 00000000
>
> Modified: lld/trunk/test/ELF/eh-frame-merge.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/eh-frame-merge.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/eh-frame-merge.s (original)
> +++ lld/trunk/test/ELF/eh-frame-merge.s Mon Feb 27 14:44:59 2017
> @@ -27,7 +27,7 @@
>  // CHECK-NEXT: ]
>  // CHECK-NEXT: Address:
>  // CHECK-NEXT: Offset:
> -// CHECK-NEXT: Size: 96
> +// CHECK-NEXT: Size: 100
>  // CHECK-NEXT: Link: 0
>  // CHECK-NEXT: Info: 0
>  // CHECK-NEXT: AddressAlignment: 8
> @@ -39,6 +39,7 @@
>  // CHECK-NEXT: 0030: 14000000 34000000 D20D0000 02000000  |
>  // CHECK-NEXT: 0040: 00000000 00000000 14000000 4C000000  |
>  // CHECK-NEXT: 0050: B90D0000 01000000 00000000 00000000  |
> +// CHECK-NEXT: 0060: 00000000                             |
>  // CHECK-NEXT: )
>  
>  // CHECK:      Name: foo
>
> Modified: lld/trunk/test/ELF/ehframe-relocation.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/ehframe-relocation.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/ehframe-relocation.s (original)
> +++ lld/trunk/test/ELF/ehframe-relocation.s Mon Feb 27 14:44:59 2017
> @@ -12,7 +12,7 @@
>  // CHECK-NEXT: ]
>  // CHECK-NEXT: Address: 0x200120
>  // CHECK-NEXT: Offset:
> -// CHECK-NEXT: Size: 48
> +// CHECK-NEXT: Size: 52
>  // CHECK-NOT: .eh_frame
>  
>  // 0x200120 = 2097440
>
> Modified: lld/trunk/test/ELF/invalid-fde-rel.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/invalid-fde-rel.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/invalid-fde-rel.s (original)
> +++ lld/trunk/test/ELF/invalid-fde-rel.s Mon Feb 27 14:44:59 2017
> @@ -33,4 +33,4 @@
>          .long 0x0
>          .long 0x0
>  
> -// CHECK:  1 .eh_frame     00000018
> +// CHECK:  1 .eh_frame     0000001c
>
> Modified: lld/trunk/test/ELF/linkerscript/eh-frame-hdr.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/eh-frame-hdr.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/linkerscript/eh-frame-hdr.s (original)
> +++ lld/trunk/test/ELF/linkerscript/eh-frame-hdr.s Mon Feb 27 14:44:59 2017
> @@ -7,7 +7,7 @@
>  # RUN: ld.lld -o %t1 --eh-frame-hdr --script %t.script %t
>  # RUN: llvm-objdump -s -section=".eh_frame_hdr" %t1 | FileCheck %s
>  
> -# CHECK:      011b033b 14000000 01000000 49000000
> +# CHECK:      011b033b 14000000 01000000 4d000000
>  # CHECK-NEXT: 30000000
>  
>  .global _start
>
> Modified: lld/trunk/test/ELF/linkerscript/symbols-synthetic.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/symbols-synthetic.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/linkerscript/symbols-synthetic.s (original)
> +++ lld/trunk/test/ELF/linkerscript/symbols-synthetic.s Mon Feb 27 14:44:59 2017
> @@ -60,7 +60,7 @@
>  # SIMPLE:      0000000000000128         .foo    00000000 .hidden _end_sec
>  # SIMPLE-NEXT: 0000000000000120         .foo    00000000 _begin_sec
>  # SIMPLE-NEXT: 0000000000000128         *ABS*   00000000 _end_sec_abs
> -# SIMPLE-NEXT: 0000000000001048         .text   00000000 _start
> +# SIMPLE-NEXT: 000000000000104c         .text   00000000 _start
>  # SIMPLE-NEXT: 0000000000000120         .foo    00000000 begin_foo
>  # SIMPLE-NEXT: 0000000000000128         .foo    00000000 end_foo
>  # SIMPLE-NEXT: 0000000000000008         *ABS*   00000000 size_foo_1
>
> Modified: lld/trunk/test/ELF/map-file.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/map-file.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/map-file.s (original)
> +++ lld/trunk/test/ELF/map-file.s Mon Feb 27 14:44:59 2017
> @@ -27,8 +27,8 @@ local:
>  .comm   common,4,16
>  
>  // CHECK:      Address          Size             Align Out     In      File    Symbol
> -// CHECK-NEXT: 0000000000200158 0000000000000030     8 .eh_frame
> -// CHECK-NEXT: 0000000000200158 0000000000000030     8         .eh_frame
> +// CHECK-NEXT: 0000000000200158 0000000000000034     8 .eh_frame
> +// CHECK-NEXT: 0000000000200158 0000000000000034     8         .eh_frame
>  // CHECK-NEXT: 0000000000201000 0000000000000015     4 .text
>  // CHECK-NEXT: 0000000000201000 000000000000000e     4         .text
>  // CHECK-NEXT: 0000000000201000 000000000000000e     4                 {{.*}}{{/|\\}}map-file.s.tmp1.o
>
> Modified: lld/trunk/test/ELF/relocatable-eh-frame.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocatable-eh-frame.s?rev=296378&r1=296377&r2=296378&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/relocatable-eh-frame.s (original)
> +++ lld/trunk/test/ELF/relocatable-eh-frame.s Mon Feb 27 14:44:59 2017
> @@ -5,7 +5,7 @@
>  # RUN: ld.lld %t -o %t.so -shared
>  # RUN: llvm-objdump -h %t.so | FileCheck --check-prefix=DSO %s
>  
> -# DSO: .eh_frame     00000030
> +# DSO: .eh_frame     00000034
>  
>  # CHECK:      Relocations [
>  # CHECK-NEXT:   Section ({{.*}}) .rela.eh_frame {
>
>
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