From: Jez Ng Date: Mon, 5 Jul 2021 05:13:30 +0000 (-0400) Subject: [lld-macho] Parse relocations quickly by assuming sorted order X-Git-Tag: llvmorg-14-init~2285 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=bcaf57cae82500f40f2348f5ee41e57b11152825;p=platform%2Fupstream%2Fllvm.git [lld-macho] Parse relocations quickly by assuming sorted order clang and gcc both seem to emit relocations in reverse order of address. That means we can match relocations to their containing subsections in `O(relocs + subsections)` rather than the `O(relocs * log(subsections))` that our previous binary search implementation required. Unfortunately, `ld -r` can still emit unsorted relocations, so we have a fallback code path for that (less common) case. Numbers for linking chromium_framework on my 3.2 GHz 16-Core Intel Xeon W: N Min Max Median Avg Stddev x 20 4.04 4.11 4.075 4.0775 0.018027756 + 20 3.95 4.02 3.98 3.985 0.020900768 Difference at 95.0% confidence -0.0925 +/- 0.0124919 -2.26855% +/- 0.306361% (Student's t, pooled s = 0.0195172) Reviewed By: #lld-macho, thakis Differential Revision: https://reviews.llvm.org/D105410 --- diff --git a/lld/MachO/ConcatOutputSection.cpp b/lld/MachO/ConcatOutputSection.cpp index 99e4558..87a6b3f 100644 --- a/lld/MachO/ConcatOutputSection.cpp +++ b/lld/MachO/ConcatOutputSection.cpp @@ -241,6 +241,8 @@ void ConcatOutputSection::finalize() { } // Process relocs by ascending address, i.e., ascending offset within isec std::vector &relocs = isec->relocs; + // FIXME: This property does not hold for object files produced by ld64's + // `-r` mode. assert(is_sorted(relocs, [](Reloc &a, Reloc &b) { return a.offset > b.offset; })); for (Reloc &r : reverse(relocs)) { diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp index fd42f57..7030501 100644 --- a/lld/MachO/InputFiles.cpp +++ b/lld/MachO/InputFiles.cpp @@ -366,6 +366,7 @@ void ObjFile::parseRelocations(ArrayRef
sectionHeaders, ArrayRef relInfos( reinterpret_cast(buf + sec.reloff), sec.nreloc); + auto subsecIt = subsecMap.rbegin(); for (size_t i = 0; i < relInfos.size(); i++) { // Paired relocations serve as Mach-O's method for attaching a // supplemental datum to a primary relocation record. ELF does not @@ -440,7 +441,24 @@ void ObjFile::parseRelocations(ArrayRef
sectionHeaders, r.addend = referentOffset; } - InputSection *subsec = findContainingSubsection(subsecMap, &r.offset); + // Find the subsection that this relocation belongs to. + // Though not required by the Mach-O format, clang and gcc seem to emit + // relocations in order, so let's take advantage of it. However, ld64 emits + // unsorted relocations (in `-r` mode), so we have a fallback for that + // uncommon case. + InputSection *subsec; + while (subsecIt != subsecMap.rend() && subsecIt->offset > r.offset) + ++subsecIt; + if (subsecIt == subsecMap.rend() || + subsecIt->offset + subsecIt->isec->getSize() <= r.offset) { + subsec = findContainingSubsection(subsecMap, &r.offset); + // Now that we know the relocs are unsorted, avoid trying the 'fast path' + // for the other relocations. + subsecIt = subsecMap.rend(); + } else { + subsec = subsecIt->isec; + r.offset -= subsecIt->offset; + } subsec->relocs.push_back(r); if (isSubtrahend) { diff --git a/lld/test/MachO/unsorted-relocations.yaml b/lld/test/MachO/unsorted-relocations.yaml new file mode 100644 index 0000000..c33b779 --- /dev/null +++ b/lld/test/MachO/unsorted-relocations.yaml @@ -0,0 +1,106 @@ +## This tests that we can handle relocations that are not sorted by address. +## llvm-mc isn't able to emit such a file, hence the use of yaml2obj. ld64 +## may emit files with unsorted relocations in `-r` mode, so we need to support +## this. + +# RUN: yaml2obj %s -o %t.o +# RUN: %lld -dylib -o %t %t.o +# RUN: llvm-objdump --macho -d %t | FileCheck %s + +# CHECK: _foo: +# CHECK-NEXT: movq _bar(%rip), %rax +# CHECK-NEXT: _bar: +# CHECK-NEXT: movq _baz(%rip), %rax +# CHECK-NEXT: _baz: +# CHECK-NEXT: movq _foo(%rip), %rax + +--- !mach-o +FileHeader: + magic: 0xFEEDFACF + cputype: 0x1000007 + cpusubtype: 0x3 + filetype: 0x1 + ncmds: 2 + sizeofcmds: 280 + flags: 0x2000 + reserved: 0x0 +LoadCommands: + - cmd: LC_SEGMENT_64 + cmdsize: 152 + segname: '' + vmaddr: 0 + vmsize: 21 + fileoff: 312 + filesize: 21 + maxprot: 7 + initprot: 7 + nsects: 1 + flags: 0 + Sections: + - sectname: __text + segname: __TEXT + addr: 0x0 + size: 21 + offset: 0x138 + align: 0 + reloff: 0x150 + nreloc: 3 + flags: 0x80000400 + reserved1: 0x0 + reserved2: 0x0 + reserved3: 0x0 + content: 488B0500000000488B0500000000488B0500000000 + relocations: + - address: 0x3 + symbolnum: 1 + pcrel: true + length: 2 + extern: true + type: 1 + scattered: false + value: 0 + - address: 0x11 + symbolnum: 0 + pcrel: true + length: 2 + extern: true + type: 1 + scattered: false + value: 0 + - address: 0xA + symbolnum: 2 + pcrel: true + length: 2 + extern: true + type: 1 + scattered: false + value: 0 + - cmd: LC_SYMTAB + cmdsize: 24 + symoff: 360 + nsyms: 3 + stroff: 408 + strsize: 16 +LinkEditData: + NameList: + - n_strx: 11 + n_type: 0xE + n_sect: 1 + n_desc: 0 + n_value: 0 + - n_strx: 6 + n_type: 0xE + n_sect: 1 + n_desc: 0 + n_value: 7 + - n_strx: 1 + n_type: 0xE + n_sect: 1 + n_desc: 0 + n_value: 14 + StringTable: + - '' + - _baz + - _bar + - _foo +...