[objcopy] Fix order of Mach-O LINKEDIT pieces during layout

[drodriguez]

Summary

The exports trie and the chained fixups where in the opposite order, and
function starts happenned before them, instead of after them.

Restore the correct order and rewrite the code to make it easier to move
around in the future if needed by reusing the Offset variable and
keeping both the StartOf... and the size of each piece together.

This was found out while trying to use the system strip in a binary
already stripped by LLVM and receiving errors around chained fixups when
we enabled those in the linker.

[jhenderson]

Added reviewers who have been more involved in Mach-O side of objcopy.

Is there a sensible test case we could have for this?

[smeenai]

The change LGTM, but a test case would be good.

Is there any documentation we can reference or explanation we can add as to why LINKEDIT needs to be in this order? I assume LLD lays things out the same way; do they have any reference for that?

[alexander-shaposhnikov]

+1 to what @smeenai said

llvm/lib/ObjCopy/MachO/MachOLayoutBuilder.cpp

246

nit: https://llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly

270

just in case (didn't have a minute to check myself) - is uint32_t used here (and on line 246) by design ?
(arithmetic operations with Offset are done on uint64_t anyway, uint32_t will be zero-extended to uint64_t)

[drodriguez]

Follow code style. Add a test. Needs D134250.

llvm/lib/ObjCopy/MachO/MachOLayoutBuilder.cpp

270

Maybe because linkedit_data_command.datasize is a uint32_t?

I have not changed this one, since I think it is trying to match the underlying format. I have changed the parameter of the lambda, since it seems to take its value from a lot of size(), which seems to be size_t, not uint32_t.

[alexander-shaposhnikov]

see a small nit above, otherwise - looks good to me.
p.s. https://reviews.llvm.org/D119671 seems to be relevant, don't know the current status of that effort though.
It would be good to review/land D134250 or D119671, alternatively i think it's reasonable to add a TODO (that we should add a test once ObjectYAML is ready) and commit this fix now.
cc: @thakis , @keith

llvm/lib/ObjCopy/MachO/MachOLayoutBuilder.cpp

245

nit: size -> Size

p.s. I'd probably rename linkEditUpdateOffset -> updateOffset

[drodriguez]

More code style

[drodriguez]

In D133974#3801858, @alexander-shaposhnikov wrote:

see a small nit above, otherwise - looks good to me.
p.s. https://reviews.llvm.org/D119671 seems to be relevant, don't know the current status of that effort though.
It would be good to review/land D134250 or D119671, alternatively i think it's reasonable to add a TODO (that we should add a test once ObjectYAML is ready) and commit this fix now.
cc: @thakis , @keith

Yes. It seems @keith and me filled the same gap. My version includes the "DataInCode" part which I wanted to test as many pieces as I could in the linkedit order.

About not waiting for D134250 (or equivalent), the test will have to be reduced a lot (and it is already missing some pieces about bindings that I don't know how to generate properly). Unless I end up in a review blockage, I will keep the dependency for the moment.

[drodriguez]

Correctly handle DyldExportsTrie

[jhenderson]

llvm/test/tools/llvm-objcopy/MachO/linkedit-order.test

2 ↗

(On Diff #461738)

layout -> laid out

[drodriguez]

Rebase on top of changes from D134569, D134571 and D134250

[drodriguez]

Fix typo

[jhenderson]

llvm/test/tools/llvm-objcopy/MachO/linkedit-order.test

31 ↗

(On Diff #462607)

FWIW, I don't think it would be too difficult to get FileCheck to support multiplication. If memory serves me rightly, it would just require adding another binop support, so could easily follow the existing addition support.

[drodriguez]

Use FileCheck mul() for multiplying. Improve test by checking the output several times. Add tests for both chained fixups and non-chained fixups.

[drodriguez]

llvm/test/tools/llvm-objcopy/MachO/linkedit-order.test

31 ↗

(On Diff #462607)

I think the operator * might not implemented because of the precedence rules. I looked a little bit into it, but I wasn't sure that my implementation was going to be good. But thanks for the clue because I saw that there was some function-like alternatives like mul and div that allows doing the multiplication and also allows me to not have to be careful with the alignment of the last piece of linkedit (I can code the alignment in the test).

[alexander-shaposhnikov]

gentle ping. @drodriguez , @smeenai

[drodriguez]

In D133974#3894409, @alexander-shaposhnikov wrote:

gentle ping. @drodriguez , @smeenai

There’s one diff in the stack that’s stuck. I pinged a couple of weeks ago but it did not advance a lot.

I hoped not to have to rework these last two without that, but it might be the only way. I will see what it can be done, but I am out for the weekend, so nothing until next week.

[drodriguez]

Rewrite without depending on D134571

llvm/lib/ObjCopy/MachO/MachOLayoutBuilder.cpp

Error MachOLayoutBuilder::layoutTail(uint64_t Offset) {
   // start with zero (unlike the case of a relocatable object file).
   const uint64_t HeaderSize =
       Is64Bit ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header);
   assert((!(O.Header.FileType == MachO::HeaderFileType::MH_OBJECT) ||
           Offset >= HeaderSize + O.Header.SizeOfCmds) &&
          "Incorrect tail offset");
   Offset = std::max(Offset, HeaderSize + O.Header.SizeOfCmds);
 
-  // The order of LINKEDIT elements is as follows:
-  // rebase info, binding info, weak binding info, lazy binding info, export
-  // trie, data-in-code, symbol table, indirect symbol table, symbol table
-  // strings, dylib codesign drs, code signature.
   uint64_t NListSize = Is64Bit ? sizeof(MachO::nlist_64) : sizeof(MachO::nlist);
   uint64_t StartOfLinkEdit = Offset;
-  uint64_t StartOfRebaseInfo = StartOfLinkEdit;
-  uint64_t StartOfBindingInfo = StartOfRebaseInfo + O.Rebases.Opcodes.size();
-  uint64_t StartOfWeakBindingInfo = StartOfBindingInfo + O.Binds.Opcodes.size();
-  uint64_t StartOfLazyBindingInfo =
-      StartOfWeakBindingInfo + O.WeakBinds.Opcodes.size();
-  uint64_t StartOfExportTrie =
-      StartOfLazyBindingInfo + O.LazyBinds.Opcodes.size();
-  uint64_t StartOfFunctionStarts = StartOfExportTrie + O.Exports.Trie.size();
-  uint64_t StartOfDyldExportsTrie =
-      StartOfFunctionStarts + O.FunctionStarts.Data.size();
-  uint64_t StartOfChainedFixups =
-      StartOfDyldExportsTrie + O.ExportsTrie.Data.size();
-  uint64_t StartOfDataInCode =
-      StartOfChainedFixups + O.ChainedFixups.Data.size();
+
+  // The order of LINKEDIT elements is as follows:
+  // rebase info, binding info, weak binding info, lazy binding info, export
+  // trie, chained fixups, dyld exports trie, function starts, data-in-code,
+  // symbol table, indirect symbol table, symbol table strings,
+  // dylib codesign drs, and code signature.
+  auto updateOffset = [&Offset](size_t Size) {
+    uint64_t PreviousOffset = Offset;
+    Offset += Size;
+    return PreviousOffset;
+  };
+
+  uint64_t StartOfRebaseInfo = updateOffset(O.Rebases.Opcodes.size());
+  uint64_t StartOfBindingInfo = updateOffset(O.Binds.Opcodes.size());
+  uint64_t StartOfWeakBindingInfo = updateOffset(O.WeakBinds.Opcodes.size());
+  uint64_t StartOfLazyBindingInfo = updateOffset(O.LazyBinds.Opcodes.size());
+  uint64_t StartOfExportTrie = updateOffset(O.Exports.Trie.size());
+  uint64_t StartOfChainedFixups = updateOffset(O.ChainedFixups.Data.size());
+  uint64_t StartOfDyldExportsTrie = updateOffset(O.ExportsTrie.Data.size());
+  uint64_t StartOfFunctionStarts = updateOffset(O.FunctionStarts.Data.size());
+  uint64_t StartOfDataInCode = updateOffset(O.DataInCode.Data.size());
   uint64_t StartOfLinkerOptimizationHint =
-      StartOfDataInCode + O.DataInCode.Data.size();
-  uint64_t StartOfSymbols =
-      StartOfLinkerOptimizationHint + O.LinkerOptimizationHint.Data.size();
+      updateOffset(O.LinkerOptimizationHint.Data.size());
+  uint64_t StartOfSymbols = updateOffset(NListSize * O.SymTable.Symbols.size());
   uint64_t StartOfIndirectSymbols =
-      StartOfSymbols + NListSize * O.SymTable.Symbols.size();
-  uint64_t StartOfSymbolStrings =
-      StartOfIndirectSymbols +
-      sizeof(uint32_t) * O.IndirectSymTable.Symbols.size();
-  uint64_t StartOfDylibCodeSignDRs =
-      StartOfSymbolStrings + StrTableBuilder.getSize();
-  uint64_t StartOfCodeSignature =
-      StartOfDylibCodeSignDRs + O.DylibCodeSignDRs.Data.size();
+      updateOffset(sizeof(uint32_t) * O.IndirectSymTable.Symbols.size());
+  uint64_t StartOfSymbolStrings = updateOffset(StrTableBuilder.getSize());
+  uint64_t StartOfDylibCodeSignDRs = updateOffset(O.DylibCodeSignDRs.Data.size());
+
+  uint64_t StartOfCodeSignature = Offset;
   uint32_t CodeSignatureSize = 0;
   if (O.CodeSignatureCommandIndex) {
     StartOfCodeSignature = alignTo(StartOfCodeSignature, 16);
 
     // Note: These calculations are to be kept in sync with the same
     // calculations performed in LLD's CodeSignatureSection.
     const uint32_t AllHeadersSize =
         alignTo(CodeSignature.FixedHeadersSize + OutputFileName.size() + 1,
                 CodeSignature.Align);

llvm/test/tools/llvm-objcopy/MachO/linkedit-order-1.test

+## This test verifies that the linkedit segment is
+## laid out in the right order.
+
+# RUN: yaml2obj %s -o %t.original
+# RUN: llvm-objcopy %t.original %t.copy
+# RUN: obj2yaml %t.copy > %t.yaml
+## Print the results several times in order to capture the linkedit offsets
+## in the order they are needed, but still following the order of the load
+## commands where they appear.
+# RUN: cat %t.yaml %t.yaml %t.yaml | FileCheck %s
+
+# CHECK: cmd:             LC_SEGMENT_64
+# CHECK: segname:         __LINKEDIT
+# CHECK: fileoff:         [[#LINKEDIT_FILEOFF:]]
+# CHECK: filesize:        [[#LINKEDIT_FILESIZE:]]
+
+# CHECK: cmd:             LC_DYLD_INFO_ONLY
+# CHECK: rebase_off:      [[#REBASE_OFF: LINKEDIT_FILEOFF]]
+# CHECK: rebase_size:     [[#REBASE_SIZE:]]
+# CHECK: bind_off:        [[#BIND_OFF: REBASE_OFF + REBASE_SIZE]]
+# CHECK: bind_size:       [[#BIND_SIZE:]]
+# CHECK: weak_bind_off:   [[#WEAK_BIND_OFF: BIND_OFF + BIND_SIZE]]
+# CHECK: weak_bind_size:  [[#WEAK_BIND_SIZE:]]
+# CHECK: lazy_bind_off:   [[#LAZY_BIND_OFF: WEAK_BIND_OFF + WEAK_BIND_SIZE]]
+# CHECK: lazy_bind_size:  [[#LAZY_BIND_SIZE:]]
+# CHECK: export_off:      [[#EXPORTS_OFF:LAZY_BIND_OFF + LAZY_BIND_SIZE]]
+# CHECK: export_size:     [[#EXPORTS_SIZE:]]
+
+# CHECK: cmd:             LC_FUNCTION_STARTS
+# CHECK: dataoff:         [[#FUNCTION_STARTS_FILEOFF: EXPORTS_OFF + EXPORTS_SIZE]]
+# CHECK: datasize:        [[#FUNCTION_STARTS_FILESIZE:]]
+
+# CHECK: cmd:             LC_DATA_IN_CODE
+# CHECK: dataoff:         [[#DATA_IN_CODE_FILEOFF: FUNCTION_STARTS_FILEOFF + FUNCTION_STARTS_FILESIZE]]
+# CHECK: datasize:        [[#DATA_IN_CODE_FILESIZE:]]
+
+## Jump over LC_CODE_SIGNATURE, which needs to be checked last
+
+# CHECK: --- !mach-o
+
+# CHECK: cmd:             LC_SYMTAB
+# CHECK: symoff:          [[#SYMTAB_SYMOFF: DATA_IN_CODE_FILEOFF + DATA_IN_CODE_FILESIZE]]
+# CHECK: nsyms:           [[#SYMTAB_NSYMS:]]
+
+## Skip over the strings table offset/size (part of LC_SYMTAB) until next loop.
+
+# CHECK: cmd:             LC_DYSYMTAB
+# CHECK: indirectsymoff:  [[#DYSYMTAB_INDIRECTSYMOFF: SYMTAB_SYMOFF + mul(SYMTAB_NSYMS, 16)]]
+# CHECK: nindirectsyms:   [[#DYSYMTAB_NINDIRECTSYMS:]]
+
+# CHECK: --- !mach-o
+
+# CHECK: cmd:             LC_SYMTAB
+# CHECK: stroff:          [[#SYMTAB_STROFF: DYSYMTAB_INDIRECTSYMOFF + mul(DYSYMTAB_NINDIRECTSYMS, 4)]]
+# CHECK: strsize:         [[#SYMTAB_STRSIZE:]]
+
+# CHECK: cmd:             LC_CODE_SIGNATURE
+## LC_CODE_SIGNATURE needs to be aligned to 16 bytes boundaries.
+# CHECK: dataoff:         [[#CODE_SIGNATURE_FILEOFF: mul(div(SYMTAB_STROFF + SYMTAB_STRSIZE + 8, 16), 16)]]
+# CHECK: datasize:        [[#CODE_SIGNATURE_FILESIZE:LINKEDIT_FILEOFF + LINKEDIT_FILESIZE - CODE_SIGNATURE_FILEOFF]]
+
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x1000007
+  cpusubtype:      0x3
+  filetype:        0x2
+  ncmds:           18
+  sizeofcmds:      1352
+  flags:           0x210085
+  reserved:        0x0
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         72
+    segname:         __PAGEZERO
+    vmaddr:          0
+    vmsize:          4294967296
+    fileoff:         0
+    filesize:        0
+    maxprot:         0
+    initprot:        0
+    nsects:          0
+    flags:           0
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         392
+    segname:         __TEXT
+    vmaddr:          4294967296
+    vmsize:          16384
+    fileoff:         0
+    filesize:        16384
+    maxprot:         5
+    initprot:        5
+    nsects:          4
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x100003F80
+        size:            16
+        offset:          0x3F80
+        align:           2
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x0
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+        reserved3:       0x0
+        content:         E80B000000E80C000000C39000000000
+      - sectname:        __stubs
+        segname:         __TEXT
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+        size:            12
+        offset:          0x3F90
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+  - cmd:             LC_SEGMENT_64
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+    vmaddr:          4295016448
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+    export_size:     48
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+    datasize:        8
+  - cmd:             LC_CODE_SIGNATURE
+    cmdsize:         16
+    dataoff:         49536
+    datasize:        536
+LinkEditData:
+  RebaseOpcodes:
+    - Opcode:          REBASE_OPCODE_SET_TYPE_IMM
+      Imm:             1
+    - Opcode:          REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+      Imm:             3
+      ExtraData:       [ 0x0 ]
+    - Opcode:          REBASE_OPCODE_DO_REBASE_IMM_TIMES
+      Imm:             1
+    - Opcode:          REBASE_OPCODE_DONE
+      Imm:             0
+  BindOpcodes:
+    - Opcode:          BIND_OPCODE_SET_DYLIB_ORDINAL_IMM
+      Imm:             1
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM
+      Imm:             0
+      Symbol:          _weak_foo
+    - Opcode:          BIND_OPCODE_SET_TYPE_IMM
+      Imm:             1
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+      Imm:             3
+      ULEBExtraData:   [ 0x8 ]
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB
+      Imm:             0
+      ULEBExtraData:   [ 0xFFFFFFFFFFFFFFF8 ]
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DO_BIND
+      Imm:             0
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_DYLIB_ORDINAL_IMM
+      Imm:             2
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM
+      Imm:             0
+      Symbol:          dyld_stub_binder
+    - Opcode:          BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+      Imm:             2
+      ULEBExtraData:   [ 0x0 ]
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DO_BIND
+      Imm:             0
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DONE
+      Imm:             0
+      Symbol:          ''
+  WeakBindOpcodes:
+    - Opcode:          BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM
+      Imm:             0
+      Symbol:          _weak_foo
+    - Opcode:          BIND_OPCODE_SET_TYPE_IMM
+      Imm:             1
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+      Imm:             3
+      ULEBExtraData:   [ 0x8 ]
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB
+      Imm:             0
+      ULEBExtraData:   [ 0xFFFFFFFFFFFFFFF8 ]
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DO_BIND
+      Imm:             0
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DONE
+      Imm:             0
+      Symbol:          ''
+  LazyBindOpcodes:
+    - Opcode:          BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB
+      Imm:             3
+      ULEBExtraData:   [ 0x0 ]
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_DYLIB_ORDINAL_IMM
+      Imm:             1
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM
+      Imm:             0
+      Symbol:          _foo
+    - Opcode:          BIND_OPCODE_DO_BIND
+      Imm:             0
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DONE
+      Imm:             0
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DONE
+      Imm:             0
+      Symbol:          ''
+    - Opcode:          BIND_OPCODE_DONE
+      Imm:             0
+      Symbol:          ''
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llvm/test/tools/llvm-objcopy/MachO/linkedit-order-2.test

+## This test verifies that the linkedit segment is
+## laid out in the right order.
+
+# RUN: yaml2obj %s -o %t.original
+# RUN: llvm-objcopy %t.original %t.copy
+# RUN: obj2yaml %t.copy > %t.yaml
+## Print the results several times in order to capture the linkedit offsets
+## in the order they are needed, but still following the order of the load
+## commands where they appear.
+# RUN: cat %t.yaml %t.yaml %t.yaml | FileCheck %s
+
+# CHECK: cmd:             LC_SEGMENT_64
+# CHECK: segname:         __LINKEDIT
+# CHECK: fileoff:         [[#LINKEDIT_FILEOFF:]]
+# CHECK: filesize:        [[#LINKEDIT_FILESIZE:]]
+
+# CHECK: cmd:             LC_DYLD_CHAINED_FIXUPS
+# CHECK: dataoff:         [[#CHAINED_FIXUPS_FILEOFF: LINKEDIT_FILEOFF]]
+# CHECK: datasize:        [[#CHAINED_FIXUPS_FILESIZE:]]
+
+# CHECK: cmd:             LC_DYLD_EXPORTS_TRIE
+# CHECK: dataoff:         [[#DYLD_EXPORTS_TRIE_FILEOFF: CHAINED_FIXUPS_FILEOFF + CHAINED_FIXUPS_FILESIZE]]
+# CHECK: datasize:        [[#DYLD_EXPORTS_TRIE_FILESIZE:]]
+
+## Jump over LC_SYMTAB and LC_DYSYMTAB, which will be checked during
+## later.
+
+# CHECK: cmd:             LC_FUNCTION_STARTS
+# CHECK: dataoff:         [[#FUNCTION_STARTS_FILEOFF: DYLD_EXPORTS_TRIE_FILEOFF + DYLD_EXPORTS_TRIE_FILESIZE]]
+# CHECK: datasize:        [[#FUNCTION_STARTS_FILESIZE:]]
+
+# CHECK: cmd:             LC_DATA_IN_CODE
+# CHECK: dataoff:         [[#DATA_IN_CODE_FILEOFF: FUNCTION_STARTS_FILEOFF + FUNCTION_STARTS_FILESIZE]]
+# CHECK: datasize:        [[#DATA_IN_CODE_FILESIZE:]]
+
+## Jump over LC_CODE_SIGNATURE, which needs to be checked last
+
+# CHECK: --- !mach-o
+
+# CHECK: cmd:             LC_SYMTAB
+# CHECK: symoff:          [[#SYMTAB_SYMOFF: DATA_IN_CODE_FILEOFF + DATA_IN_CODE_FILESIZE]]
+# CHECK: nsyms:           [[#SYMTAB_NSYMS:]]
+
+## Skip over the strings table offset/size (part of LC_SYMTAB) until next loop.
+
+# CHECK: cmd:             LC_DYSYMTAB
+# CHECK: indirectsymoff:  [[#DYSYMTAB_INDIRECTSYMOFF: SYMTAB_SYMOFF + mul(SYMTAB_NSYMS, 16)]]
+# CHECK: nindirectsyms:   [[#DYSYMTAB_NINDIRECTSYMS:]]
+
+# CHECK: --- !mach-o
+
+# CHECK: cmd:             LC_SYMTAB
+# CHECK: stroff:          [[#SYMTAB_STROFF: DYSYMTAB_INDIRECTSYMOFF + mul(DYSYMTAB_NINDIRECTSYMS, 4)]]
+# CHECK: strsize:         [[#SYMTAB_STRSIZE:]]
+
+# CHECK: cmd:             LC_CODE_SIGNATURE
+## LC_CODE_SIGNATURE needs to be aligned to 16 bytes boundaries.
+# CHECK: dataoff:         [[#CODE_SIGNATURE_FILEOFF: mul(div(SYMTAB_STROFF + SYMTAB_STRSIZE + 8, 16), 16)]]
+# CHECK: datasize:        [[#CODE_SIGNATURE_FILESIZE:LINKEDIT_FILEOFF + LINKEDIT_FILESIZE - CODE_SIGNATURE_FILEOFF]]
+
+--- !mach-o
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