[lld] r221831 - [mach-o] Sort GOT entries by name to make links reproducible
Jim Grosbach
grosbach at apple.com
Wed Nov 12 22:04:47 PST 2014
Woot! Very, very cool. Today, self hosting LLD. Tomorrow, self hosting clang via LLD.
Ok. Maybe not literally tomorrow, but we are on the path!
Sent from my iPhone
> On Nov 12, 2014, at 3:34 PM, Nick Kledzik <kledzik at apple.com> wrote:
>
> Author: kledzik
> Date: Wed Nov 12 17:34:23 2014
> New Revision: 221831
>
> URL: http://llvm.org/viewvc/llvm-project?rev=221831&view=rev
> Log:
> [mach-o] Sort GOT entries by name to make links reproducible
>
> The GOT slots were being laid out in a random order by the GOTPass which
> caused randomness in the output file.
>
> Note: With this change lld now bootstraps on darwin. That is:
> 1) link lld using system linker to make lld.1
> 2) link lld using lld.1 to make lld.2
> 3) link lld using lld.2 to make lld.3
> Now lld.2 and lld.3 are identical.
>
> Added:
> lld/trunk/test/mach-o/got-order.yaml
> Modified:
> lld/trunk/lib/ReaderWriter/MachO/GOTPass.cpp
>
> Modified: lld/trunk/lib/ReaderWriter/MachO/GOTPass.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/MachO/GOTPass.cpp?rev=221831&r1=221830&r2=221831&view=diff
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/MachO/GOTPass.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/MachO/GOTPass.cpp Wed Nov 12 17:34:23 2014
> @@ -52,8 +52,8 @@ namespace mach_o {
> //
> class GOTEntryAtom : public SimpleDefinedAtom {
> public:
> - GOTEntryAtom(const File &file, bool is64)
> - : SimpleDefinedAtom(file), _is64(is64) { }
> + GOTEntryAtom(const File &file, bool is64, StringRef name)
> + : SimpleDefinedAtom(file), _is64(is64), _name(name) { }
>
> ContentType contentType() const override {
> return DefinedAtom::typeGOT;
> @@ -77,8 +77,13 @@ public:
> return llvm::makeArrayRef(zeros, size());
> }
>
> + StringRef slotName() const {
> + return _name;
> + }
> +
> private:
> const bool _is64;
> + StringRef _name;
> };
>
>
> @@ -116,9 +121,17 @@ private:
> }
> }
>
> - // add all created GOT Atoms to master file
> + // Sort and add all created GOT Atoms to master file
> + std::vector<const GOTEntryAtom *> entries;
> + entries.reserve(_targetToGOT.size());
> for (auto &it : _targetToGOT)
> - mergedFile->addAtom(*it.second);
> + entries.push_back(it.second);
> + std::sort(entries.begin(), entries.end(),
> + [](const GOTEntryAtom *left, const GOTEntryAtom *right) {
> + return (left->slotName().compare(right->slotName()) < 0);
> + });
> + for (const GOTEntryAtom *slot : entries)
> + mergedFile->addAtom(*slot);
> }
>
> bool shouldReplaceTargetWithGOTAtom(const Atom *target, bool canBypassGOT) {
> @@ -142,7 +155,7 @@ private:
> auto pos = _targetToGOT.find(target);
> if (pos == _targetToGOT.end()) {
> GOTEntryAtom *gotEntry = new (_file.allocator())
> - GOTEntryAtom(_file, _context.is64Bit());
> + GOTEntryAtom(_file, _context.is64Bit(), target->name());
> _targetToGOT[target] = gotEntry;
> const ArchHandler::ReferenceInfo &nlInfo = _archHandler.stubInfo().
> nonLazyPointerReferenceToBinder;
>
> Added: lld/trunk/test/mach-o/got-order.yaml
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/mach-o/got-order.yaml?rev=221831&view=auto
> ==============================================================================
> --- lld/trunk/test/mach-o/got-order.yaml (added)
> +++ lld/trunk/test/mach-o/got-order.yaml Wed Nov 12 17:34:23 2014
> @@ -0,0 +1,134 @@
> +# RUN: lld -flavor darwin -arch x86_64 %s -o %t %p/Inputs/libSystem.yaml
> +# RUN: llvm-objdump -bind %t | FileCheck %s
> +#
> +# Test that GOT slots are sorted by name
> +#
> +
> +--- !mach-o
> +arch: x86_64
> +file-type: MH_OBJECT
> +flags: [ MH_SUBSECTIONS_VIA_SYMBOLS ]
> +sections:
> + - segment: __TEXT
> + section: __text
> + type: S_REGULAR
> + attributes: [ S_ATTR_PURE_INSTRUCTIONS, S_ATTR_SOME_INSTRUCTIONS ]
> + address: 0x0000000000000000
> + content: [ 0x55, 0x48, 0x89, 0xE5, 0x48, 0x8B, 0x0D, 0x00,
> + 0x00, 0x00, 0x00, 0x48, 0x8B, 0x05, 0x00, 0x00,
> + 0x00, 0x00, 0x8B, 0x00, 0x03, 0x01, 0x48, 0x8B,
> + 0x0D, 0x00, 0x00, 0x00, 0x00, 0x03, 0x01, 0x5D,
> + 0xC3 ]
> + relocations:
> + - offset: 0x00000019
> + type: X86_64_RELOC_GOT_LOAD
> + length: 2
> + pc-rel: true
> + extern: true
> + symbol: 2
> + - offset: 0x0000000E
> + type: X86_64_RELOC_GOT_LOAD
> + length: 2
> + pc-rel: true
> + extern: true
> + symbol: 1
> + - offset: 0x00000007
> + type: X86_64_RELOC_GOT_LOAD
> + length: 2
> + pc-rel: true
> + extern: true
> + symbol: 3
> +global-symbols:
> + - name: _func
> + type: N_SECT
> + scope: [ N_EXT ]
> + sect: 1
> + value: 0x0000000000000000
> +undefined-symbols:
> + - name: _aaa
> + type: N_UNDF
> + scope: [ N_EXT ]
> + value: 0x0000000000000000
> + - name: _fff
> + type: N_UNDF
> + scope: [ N_EXT ]
> + value: 0x0000000000000000
> + - name: _zzz
> + type: N_UNDF
> + scope: [ N_EXT ]
> + value: 0x0000000000000000
> +
> +--- !mach-o
> +arch: x86_64
> +file-type: MH_OBJECT
> +flags: [ MH_SUBSECTIONS_VIA_SYMBOLS ]
> +sections:
> + - segment: __TEXT
> + section: __text
> + type: S_REGULAR
> + attributes: [ S_ATTR_PURE_INSTRUCTIONS, S_ATTR_SOME_INSTRUCTIONS ]
> + address: 0x0000000000000000
> + content: [ 0x55, 0x48, 0x89, 0xE5, 0x48, 0x8B, 0x0D, 0x00,
> + 0x00, 0x00, 0x00, 0x48, 0x8B, 0x05, 0x00, 0x00,
> + 0x00, 0x00, 0x8B, 0x00, 0x03, 0x01, 0x48, 0x8B,
> + 0x0D, 0x00, 0x00, 0x00, 0x00, 0x03, 0x01, 0x5D,
> + 0xC3 ]
> + relocations:
> + - offset: 0x00000019
> + type: X86_64_RELOC_GOT_LOAD
> + length: 2
> + pc-rel: true
> + extern: true
> + symbol: 2
> + - offset: 0x0000000E
> + type: X86_64_RELOC_GOT_LOAD
> + length: 2
> + pc-rel: true
> + extern: true
> + symbol: 1
> + - offset: 0x00000007
> + type: X86_64_RELOC_GOT_LOAD
> + length: 2
> + pc-rel: true
> + extern: true
> + symbol: 3
> +global-symbols:
> + - name: _main
> + type: N_SECT
> + scope: [ N_EXT ]
> + sect: 1
> + value: 0x0000000000000000
> +undefined-symbols:
> + - name: _bar
> + type: N_UNDF
> + scope: [ N_EXT ]
> + value: 0x0000000000000000
> + - name: _foo
> + type: N_UNDF
> + scope: [ N_EXT ]
> + value: 0x0000000000000000
> + - name: _zazzle
> + type: N_UNDF
> + scope: [ N_EXT ]
> + value: 0x0000000000000000
> +
> +--- !mach-o
> +arch: x86_64
> +file-type: MH_DYLIB
> +install-name: /usr/lib/libfoobar.dylib
> +exports:
> + - name: _bar
> + - name: _zazzle
> + - name: _foo
> + - name: _aaa
> + - name: _fff
> + - name: _zzz
> +...
> +
> +
> +# CHECK: __DATA __got {{[0-9a-zA-Z _]+}} pointer 0 libfoobar _aaa
> +# CHECK-NEXT: __DATA __got {{[0-9a-zA-Z _]+}} pointer 0 libfoobar _bar
> +# CHECK-NEXT: __DATA __got {{[0-9a-zA-Z _]+}} pointer 0 libfoobar _fff
> +# CHECK-NEXT: __DATA __got {{[0-9a-zA-Z _]+}} pointer 0 libfoobar _foo
> +# CHECK-NEXT: __DATA __got {{[0-9a-zA-Z _]+}} pointer 0 libfoobar _zazzle
> +# CHECK-NEXT: __DATA __got {{[0-9a-zA-Z _]+}} pointer 0 libfoobar _zzz
>
>
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