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Update ReleaseNotes for lld 9.0.
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‎lld/docs/ReleaseNotes.rst

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@@ -8,10 +8,12 @@ lld 9.0.0 Release Notes
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Introduction
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============
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This document contains the release notes for the lld linker, release 9.0.0.
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Here we describe the status of lld, including major improvements
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from the previous release. All lld releases may be downloaded
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from the `LLVM releases web site <https://llvm.org/releases/>`_.
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lld is a high-performance linker that supports ELF (Unix), COFF
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(Windows), Mach-O (macOS), MinGW and WebAssembly. lld is
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command-line-compatible with GNU linkers and Microsoft link.exe and is
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significantly faster than the system default linkers.
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lld 9.0 has lots of feature improvements and bug fixes.
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Non-comprehensive list of changes in this release
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=================================================
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* ld.lld now has typo suggestions for flags:
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``$ ld.lld --call-shared`` now prints
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``unknown argument '--call-shared', did you mean '--call_shared'``.
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(`r361518 <https://reviews.llvm.org/rL361518>`_)
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* ``--allow-shlib-undefined`` and ``--no-allow-shlib-undefined``
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options are added. ``--no-allow-shlib-undefined`` is the default for
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executables.
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(`r352826 <https://reviews.llvm.org/rL352826>`_)
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* ``-nmagic`` and ``-omagic`` options are fully supported.
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(`r360593 <https://reviews.llvm.org/rL360593>`_)
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* Segment layout has changed. PT_GNU_RELRO, which was previously
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placed in the middle of readable/writable PT_LOAD segments, is now
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placed at the beginning of them. This change permits lld-produced
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ELF files to be read correctly by GNU strip older than 2.31, which
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has a bug to discard a PT_GNU_RELRO in the former layout.
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* ``-z common-page-size`` is supported.
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(`r360593 <https://reviews.llvm.org/rL360593>`_)
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* Diagnostics messages have improved. A new flag ``--vs-diagnostics``
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alters the format of diagnostic output to enable source hyperlinks
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in Microsoft Visual Studio IDE.
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* Linker script compatibility with GNU BFD linker has generally improved.
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* The clang ``--dependent-library`` form of autolinking is supported.
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This feature is added to implement the Windows-style autolinking for
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Unix. On Unix, in order to use a library, you usually have to
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include a header file provided by the library and then explicitly
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link the library with the linker ``-l`` option. On Windows, header
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files usually contain pragmas that list needed libraries. Compilers
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copies that information to object files, so that linkers can
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automatically link needed libraries. ``--dependent-library`` is
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added for implementing that Windows semantics on Unix.
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(`r360984 <https://reviews.llvm.org/rL360984>`_)
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* AArch64 BTI and PAC are supported.
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(`r362793 <https://reviews.llvm.org/rL362793>`_)
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* lld now supports replacing ``JAL`` with ``JALX`` instructions in case
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of MIPS - microMIPS cross-mode jumps.
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of MIPS ↔ microMIPS cross-mode jumps.
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(`r354311 <https://reviews.llvm.org/rL354311>`_)
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* lld now creates LA25 thunks for MIPS R6 code.
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(`r354312 <https://reviews.llvm.org/rL354312>`_)
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* Put MIPS-specific .reginfo, .MIPS.options, and .MIPS.abiflags sections
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into corresponding PT_MIPS_REGINFO, PT_MIPS_OPTIONS, and PT_MIPS_ABIFLAGS
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segments.
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* The quality of RISC-V and PowerPC ports have greatly improved. Many
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applications can now be linked by lld. PowerPC64 is now almost
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production ready.
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* The Linux kernel for arm32_7, arm64, ppc64le and x86_64 can now be
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linked by lld.
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* x86-64 TLSDESC is supported.
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(`r361911 <https://reviews.llvm.org/rL361911>`_,
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`r362078 <https://reviews.llvm.org/rL362078>`_)
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* DF_STATIC_TLS flag is set for i386 and x86-64 when needed.
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(`r353293 <https://reviews.llvm.org/rL353293>`_,
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`r353378 <https://reviews.llvm.org/rL353378>`_)
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* The experimental partitioning feature is added to allow a program to
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be split into multiple pieces.
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The feature allows you semi-automatically split a single program
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into multiple ELF files called "partitions". Since all partitions
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share the same memory address space and don't use PLT/GOT, split
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programs run as fast as regular programs.
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With the mechanism, you can start a program only with a "main"
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partition and load remaining partitions on-demand. For example, you
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can split a web browser into a main partition and a PDF reader
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sub-partition and load the PDF reader partition only when a user
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tries to open a PDF file.
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See https://lld.llvm.org/Partitions.html for more information.
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* If "-" is given as an output filename, lld write the final result
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to the standard output. Previously, it created a file "-" in the
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current directory.
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(`r351852 <https://reviews.llvm.org/rL351852>`_)
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* ``-z ifunc-noplt`` option is added to reduce IFunc function call
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overhead in a freestanding environment such as the OS kernel.
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Functions resolved by the IFunc mechanism are usually dispatched via
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PLT and thus slower than regular functions because of the cost of
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indirection. With ``-z ifunc-noplt``, you can eliminate it by doing
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text relocations at load-time. You need a special loader to utilize
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this feature. This feature is added for the FreeBSD kernel but can
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be used by any operating systems.
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(`r360685 <https://reviews.llvm.org/rL360685>`_)
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* ``--undefined-glob`` option is added. The new option is an extension
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to ``--undefined`` to take a glob pattern instead of a single symbol
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name.
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(`r363396 <https://reviews.llvm.org/rL363396>`_)
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COFF Improvements
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-----------------
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* Like the ELF driver, lld-link now has typo suggestions for flags.
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(`r361518 <https://reviews.llvm.org/rL361518>`_)
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* lld-link now correctly reports duplicate symbol errors for obj files
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that were compiled with /Gy.
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* lld-link now correctly reports duplicate symbol errors for object
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files that were compiled with ``/Gy``.
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(`r352590 <https://reviews.llvm.org/rL352590>`_)
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* lld-link now correctly reports duplicate symbol errors when several res
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input files define resources with the same type, name, and language.
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This can be demoted to a warning using ``/force:multipleres``.
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* lld-link now correctly reports duplicate symbol errors when several
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resource (.res) input files define resources with the same type,
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name and language. This can be demoted to a warning using
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``/force:multipleres``.
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(`r359829 <https://reviews.llvm.org/rL359829>`_)
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* lld-link now rejects more than one resource obj input files, matching
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link.exe. Previously, lld-link would silently ignore all but one.
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If you hit this: Don't pass resource obj files to the linker, instead pass
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res files to the linker directly. Don't put res files in static libraries,
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pass them on the command line.
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* lld-link now rejects more than one resource object input files,
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matching link.exe. Previously, lld-link would silently ignore all
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but one. If you hit this: Don't pass resource object files to the
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linker, instead pass res files to the linker directly. Don't put
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resource files in static libraries, pass them on the command line.
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(`r359749 <https://reviews.llvm.org/rL359749>`_)
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* Having more than two ``/natvis:`` now works correctly; it used to not
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work for larger binaries before.
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(`r327895 <https://reviews.llvm.org/rL327895>`_)
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* Undefined symbols are now printed only in demangled form. Pass
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``/demangle:no`` to see raw symbol names instead.
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* The following flags have been added: ``/functionpadmin``, ``/swaprun:``,
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``/threads:no``
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(`r355878 <https://reviews.llvm.org/rL355878>`_)
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* Several speed and memory usage improvements.
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* Range extension thunks are now created for ARM64, if needed
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* Range extension thunks are now created for ARM64, if needed.
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* lld-link now supports resource object files created by GNU windres and
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MS cvtres, not only llvm-cvtres
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MS cvtres, not only llvm-cvtres.
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* The generated thunks for delayimports now share the majority of code
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among thunks, significantly reducing the overhead of using delayimport
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among thunks, significantly reducing the overhead of using delayimport.
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(`r365823 <https://reviews.llvm.org/rL365823>`_)
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* ``IMAGE_REL_ARM{,64}_REL32`` relocations are supported.
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(`r352325 <https://reviews.llvm.org/rL352325>`_)
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* Range extension thunks for AArch64 are now supported, so lld can
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create large executables for Windows/ARM64.
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(`r352929 <https://reviews.llvm.org/rL352929>`_)
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* The following flags have been added:
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``/functionpadmin`` (`r354716 <https://reviews.llvm.org/rL354716>`_),
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``/swaprun:`` (`r359192 <https://reviews.llvm.org/rL359192>`_),
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``/threads:no`` (`r355029 <https://reviews.llvm.org/rL355029>`_),
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``/filealign`` (`r361634 <https://reviews.llvm.org/rL361634>`_)
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WebAssembly Improvements
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------------------------
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* Imports from custom module names are supported.
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(`r352828 <https://reviews.llvm.org/rL352828>`_)
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* Symbols that are in llvm.used are no exported by default.
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(`r353364 <https://reviews.llvm.org/rL353364>`_)
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* Initial support for PIC and dynamic linking has landed.
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(`r357022 <https://reviews.llvm.org/rL357022>`_)
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* wasm-ld now add ``__start_``/``__stop_`` symbols for data sections.
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(`r361236 <https://reviews.llvm.org/rL361236>`_)
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* wasm-ld now doesn't report an error on archives without a symbol index.
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(`r364338 <https://reviews.llvm.org/rL364338>`_)
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* The following flags have been added:
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``--emit-relocs`` (`r361635 <https://reviews.llvm.org/rL361635>`_),
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``--wrap`` (`r361639 <https://reviews.llvm.org/rL361639>`_),
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``--trace`` and ``--trace-symbol``
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(`r353264 <https://reviews.llvm.org/rL353264>`_).
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MinGW Improvements
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------------------
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DWARF exception handling with libgcc and gcc's crtend.o.
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* lld now also handles DWARF unwind info generated by GCC, when linking
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with libgcc
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* Many more GNU ld options are now supported, which e.g. allows the lld
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MinGW frontend to be called by GCC
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with libgcc.
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* PDB output can be requested without manually specifying the PDB file
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name, with the new option ``-pdb=`` with an empty value to the option.
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(The old existing syntax ``-pdb <filename>`` was more cumbersome to use
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with an empty parameter value.)
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* ``--no-insert-timestamp`` option is added as an alias to ``/timestamp:0``.
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(`r353145 <https://reviews.llvm.org/rL353145>`_)
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* Many more GNU ld options are now supported, which e.g. allows the lld
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MinGW frontend to be called by GCC.
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* The following options are added: ``--exclude-all-symbols``,
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``--appcontainer``, ``--emit-relocs``, ``--wrap``, ``--undefined``

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