3fcb0eeb15
Debug sections contain a large amount of data. In order not to bloat the size of the final binary, we remove them and instead emit STABS symbols for `dsymutil` and the debugger to locate their contents in the object files. With this diff, `dsymutil` is able to locate the debug info. However, we need a few more features before `lldb` is able to work well with our binaries -- e.g. having `LC_DYSYMTAB` accurately reflect the number of local symbols, emitting `LC_UUID`, and more. Those will be handled in follow-up diffs. Note also that the STABS we emit differ slightly from what ld64 does. First, we emit the path to the source file as one `N_SO` symbol instead of two. (`ld64` emits one `N_SO` for the dirname and one of the basename.) Second, we do not emit `N_BNSYM` and `N_ENSYM` STABS to mark the start and end of functions, because the `N_FUN` STABS already serve that purpose. @clayborg recommended these changes based on his knowledge of what the debugging tools look for. Additionally, this current implementation doesn't accurately reflect the size of function symbols. It uses the size of their containing sectioins as a proxy, but that is only accurate if `.subsections_with_symbols` is set, and if there isn't an `N_ALT_ENTRY` in that particular subsection. I think we have two options to solve this: 1. We can split up subsections by symbol even if `.subsections_with_symbols` is not set, but include constraints to ensure those subsections retain their order in the final output. This is `ld64`'s approach. 2. We could just add a `size` field to our `Symbol` class. This seems simpler, and I'm more inclined toward it, but I'm not sure if there are use cases that it doesn't handle well. As such I'm punting on the decision for now. Reviewed By: clayborg Differential Revision: https://reviews.llvm.org/D89257
65 lines
1.7 KiB
C++
65 lines
1.7 KiB
C++
//===- OutputSegment.h ------------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLD_MACHO_OUTPUT_SEGMENT_H
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#define LLD_MACHO_OUTPUT_SEGMENT_H
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#include "OutputSection.h"
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#include "lld/Common/LLVM.h"
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namespace lld {
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namespace macho {
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namespace segment_names {
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constexpr const char pageZero[] = "__PAGEZERO";
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constexpr const char text[] = "__TEXT";
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constexpr const char data[] = "__DATA";
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constexpr const char linkEdit[] = "__LINKEDIT";
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constexpr const char dataConst[] = "__DATA_CONST";
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constexpr const char ld[] = "__LD"; // output only with -r
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constexpr const char dwarf[] = "__DWARF";
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} // namespace segment_names
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class OutputSection;
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class InputSection;
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class OutputSegment {
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public:
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const OutputSection *firstSection() const { return sections.front(); }
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const OutputSection *lastSection() const { return sections.back(); }
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void addOutputSection(OutputSection *os);
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void sortOutputSections(
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llvm::function_ref<bool(OutputSection *, OutputSection *)> comparator) {
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llvm::stable_sort(sections, comparator);
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}
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const std::vector<OutputSection *> &getSections() const { return sections; }
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size_t numNonHiddenSections() const;
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uint64_t fileOff = 0;
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StringRef name;
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uint32_t maxProt = 0;
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uint32_t initProt = 0;
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uint8_t index;
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private:
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std::vector<OutputSection *> sections;
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};
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extern std::vector<OutputSegment *> outputSegments;
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OutputSegment *getOrCreateOutputSegment(StringRef name);
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} // namespace macho
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} // namespace lld
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#endif
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