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========================
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lld 14.0.0 Release Notes
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========================
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.. contents::
:local:
.. warning::
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These are in-progress notes for the upcoming LLVM 14.0.0 release.
Don't try to link to the 4.0 release notes llvm-svn: 294659
2017-02-10 07:27:17 +08:00
Release notes for previous releases can be found on
ReleaseNotes: update links to use https llvm-svn: 341788
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`the Download Page <https://releases.llvm.org/download.html>`_.
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Introduction
============
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This document contains the release notes for the lld linker, release 14.0.0.
ReleaseNotes: user lower-case for lld in the text llvm-svn: 325869
2018-02-23 16:27:38 +08:00
Here we describe the status of lld, including major improvements
from the previous release. All lld releases may be downloaded
ReleaseNotes: update links to use https llvm-svn: 341788
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from the `LLVM releases web site <https://llvm.org/releases/>`_.
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Non-comprehensive list of changes in this release
=================================================
ELF Improvements
----------------
[ELF] Add --export-dynamic-symbol-list This is available in GNU ld 2.35 and can be seen as a shortcut for multiple --export-dynamic-symbol, or a --dynamic-list variant without the symbolic intention. In the long term, this option probably should be preferred over --dynamic-list. Reviewed By: peter.smith Differential Revision: https://reviews.llvm.org/D107317
2021-08-04 00:01:03 +08:00
* ``--export-dynamic-symbol-list`` has been added.
(`D107317 <https://reviews.llvm.org/D107317>`_)
[ELF] Add --why-extract= to query why archive members/lazy object files are extracted Similar to D69607 but for archive member extraction unrelated to GC. This patch adds --why-extract=. Prior art: GNU ld -M prints ``` Archive member included to satisfy reference by file (symbol) a.a(a.o) main.o (a) b.a(b.o) (b()) ``` -M is mainly for input section/symbol assignment <-> output section mapping (often huge output) and the information may appear ad-hoc. Apple ld64 ``` __Z1bv forced load of b.a(b.o) _a forced load of a.a(a.o) ``` It doesn't say the reference file. Arm's proprietary linker ``` Selecting member vsnprintf.o(c_wfu.l) to define vsnprintf. ... Loading member vsnprintf.o from c_wfu.l. definition: vsnprintf reference : _printf_a ``` --- --why-extract= gives the user the full data (which is much shorter than GNU ld -Map). It is easy to track a chain of references to one archive member with a one-liner, e.g. ``` % ld.lld main.o a_b.a b_c.a c.a -o /dev/null --why-extract=- | tee stdout reference extracted symbol main.o a_b.a(a_b.o) a a_b.a(a_b.o) b_c.a(b_c.o) b() b_c.a(b_c.o) c.a(c.o) c() % ruby -ane 'BEGIN{p={}}; p[$F[1]]=[$F[0],$F[2]] if $.>1; END{x="c.a(c.o)"; while y=p[x]; puts "#{y[0]} extracts #{x} to resolve #{y[1]}"; x=y[0] end}' stdout b_c.a(b_c.o) extracts c.a(c.o) to resolve c() a_b.a(a_b.o) extracts b_c.a(b_c.o) to resolve b() main.o extracts a_b.a(a_b.o) to resolve a ``` Archive member extraction happens before --gc-sections, so this may not be a live path under --gc-sections, but I think it is a good approximation in practice. * Specifying a file avoids output interleaving with --verbose. * Required `=` prevents accidental overwrite of an input if the user forgets `=`. (Most of compiler drivers' long options accept `=` but not ` `) Differential Revision: https://reviews.llvm.org/D109572
2021-09-21 00:52:30 +08:00
* ``--why-extract`` has been added to query why archive members/lazy object files are extracted.
(`D109572 <https://reviews.llvm.org/D109572>`_)
[ELF] Don't fall back to .text for e_entry We have the rule to simulate (https://sourceware.org/binutils/docs/ld/Entry-Point.html), but the behavior is questionable (https://sourceware.org/pipermail/binutils/2021-September/117929.html). gold doesn't fall back to .text. The behavior is unlikely relied by projects (there is even a warning for executable links), so let's just delete this fallback path. Reviewed By: jhenderson, peter.smith Differential Revision: https://reviews.llvm.org/D110014
2021-09-21 00:35:12 +08:00
* ``e_entry`` no longer falls back to the address of ``.text`` if the entry symbol does not exist.
Instead, a value of 0 will be written.
(`D110014 <https://reviews.llvm.org/D110014>`_)
[NFC] Fix typos in release notes. Reviewed By: ldionne, Mordante, MaskRay Differential Revision: https://reviews.llvm.org/D115685
2021-12-14 08:08:18 +08:00
* If ``-Map`` is specified, ``--cref`` will be printed to the specified file.
[ELF] --cref: If -Map is specified, print to the map file PR48282: This behavior matches GNU ld and gold. Reviewed By: markj Differential Revision: https://reviews.llvm.org/D114663
2021-11-30 06:14:53 +08:00
(`D114663 <https://reviews.llvm.org/D114663>`_)
Update release notes. llvm-svn: 342754
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[ELF] Implement TLSDESC for x86-32 `-z rela` is also supported. Tested with: ``` cat > ./a.c <<eof #include <assert.h> int foo(); int bar(); int main() { assert(foo() == 2); assert(foo() == 4); assert(bar() == 2); assert(bar() == 4); } eof cat > ./b.c <<eof #include <stdio.h> __thread int tls0; extern __thread int tls1; int foo() { return ++tls0 + ++tls1; } static __thread int tls2, tls3; int bar() { return ++tls2 + ++tls3; } eof echo '__thread int tls1;' > ./c.c sed 's/ /\t/' > ./Makefile <<'eof' .MAKE.MODE = meta curDirOk=true CC := gcc -m32 -g -fpic -mtls-dialect=gnu2 LDFLAGS := -m32 -Wl,-rpath=. all: a0 a1 a2 run: all ./a0 && ./a1 && ./a2 c.so: c.o; ${LINK.c} -shared $> -o $@ bc.so: b.o c.o; ${LINK.c} -shared $> -o $@ b.so: b.o c.so; ${LINK.c} -shared $> -o $@ a0: a.o b.o c.o; ${LINK.c} $> -o $@ a1: a.o b.so; ${LINK.c} $> -o $@ a2: a.o bc.so; ${LINK.c} $> -o $@ eof ``` and glibc `elf/tst-gnu2-tls1`. `/usr/local/bin/ld` points to the freshly built `lld`. `bmake run && bmake CFLAGS=-O1 run` => ok. Differential Revision: https://reviews.llvm.org/D112582
2021-10-29 08:52:03 +08:00
Architecture specific changes:
* The x86-32 port now supports TLSDESC (``-mtls-dialect=gnu2``).
[docs] Fix docs-lld-html
2021-10-29 09:44:44 +08:00
(`D112582 <https://reviews.llvm.org/D112582>`_)
[ELF] Support non-RAX/non-adjacent R_X86_64_GOTPC32_TLSDESC/R_X86_64_TLSDESC_CALL The current TLSDESC optimization code assumes: ``` leaq x@tlsdesc(%rip), %rax call *x@tlscall(%rax) # adjacent ``` From https://gitlab.freedesktop.org/mesa/mesa/-/issues/5665 , it seems that the two instructions may not be adjacent in GCC 10's output: ``` leaq x@tlsdesc(%rip), %rax something else call *x@tlscall(%rax) ``` This patch supports the case. While here, support non-RAX registers for R_X86_64_GOTPC32_TLSDESC, in case the compiler generates inefficient: ``` leaq x@tlsdesc(%rip), %rcx # or %rdx, %rbx, %rdi, ... movq %rcx, %rax call *x@tlscall(%rax) # GNU ld/gold error for non-RAX ``` Differential Revision: https://reviews.llvm.org/D114416
2021-11-24 02:30:11 +08:00
* The x86-64 port now handles non-RAX/non-adjacent ``R_X86_64_GOTPC32_TLSDESC``
and ``R_X86_64_TLSDESC_CALL`` (``-mtls-dialect=gnu2``).
(`D114416 <https://reviews.llvm.org/D114416>`_)
[ELF] Make --no-relax disable R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX GOT optimization This brings back the original version of D81359. I have found several use cases now. * Unlike GNU ld, LLD's relocation processing is one pass. If we decide to optimize(relax) R_X86_64_{,REX_}GOTPCRELX, we will suppress GOT generation and cannot undo the decision later. Optimizing R_X86_64_REX_GOTPCRELX can usually make it easy to hit `relocation R_X86_64_REX_GOTPCRELX out of range` because the distance to GOT is usually shorter. Without --no-relax, the user has to recompile with `-Wa,-mrelax-relocations=no`. * The option would help during my investigationg of the root cause of https://git.kernel.org/linus/09e43968db40c33a73e9ddbfd937f46d5c334924 * There is need for relaxation for AArch64 & RISC-V. Implementing this for x86-64 improves consistency with little target-specific cost (two-line X86_64.cpp change). Reviewed By: alexander-shaposhnikov Differential Revision: https://reviews.llvm.org/D113615
2021-11-13 01:47:31 +08:00
* For x86-64, ``--no-relax`` now suppresses ``R_X86_64_GOTPCRELX`` and
``R_X86_64_REX_GOTPCRELX`` GOT optimization
(`D113615 <https://reviews.llvm.org/D113615>`_)
[ELF] Implement TLSDESC for x86-32 `-z rela` is also supported. Tested with: ``` cat > ./a.c <<eof #include <assert.h> int foo(); int bar(); int main() { assert(foo() == 2); assert(foo() == 4); assert(bar() == 2); assert(bar() == 4); } eof cat > ./b.c <<eof #include <stdio.h> __thread int tls0; extern __thread int tls1; int foo() { return ++tls0 + ++tls1; } static __thread int tls2, tls3; int bar() { return ++tls2 + ++tls3; } eof echo '__thread int tls1;' > ./c.c sed 's/ /\t/' > ./Makefile <<'eof' .MAKE.MODE = meta curDirOk=true CC := gcc -m32 -g -fpic -mtls-dialect=gnu2 LDFLAGS := -m32 -Wl,-rpath=. all: a0 a1 a2 run: all ./a0 && ./a1 && ./a2 c.so: c.o; ${LINK.c} -shared $> -o $@ bc.so: b.o c.o; ${LINK.c} -shared $> -o $@ b.so: b.o c.so; ${LINK.c} -shared $> -o $@ a0: a.o b.o c.o; ${LINK.c} $> -o $@ a1: a.o b.so; ${LINK.c} $> -o $@ a2: a.o bc.so; ${LINK.c} $> -o $@ eof ``` and glibc `elf/tst-gnu2-tls1`. `/usr/local/bin/ld` points to the freshly built `lld`. `bmake run && bmake CFLAGS=-O1 run` => ok. Differential Revision: https://reviews.llvm.org/D112582
2021-10-29 08:52:03 +08:00
[ELF] Add convenience TableGen classes to enforce two dashes for options not supported by GNU ld Announced on https://lists.llvm.org/pipermail/llvm-dev/2020-May/141416.html For many options, we have to support either one or two dash to be compatible with GNU ld. For newer and lld specific options, we can enforce strict double dashes. Affected options: * --thinlto-* * --lto-* * --shuffle-sections= This patch does not change `-plugin-opt=*` because clang driver passes `-plugin-opt=*` and I don't intend to cause churn. In 2000, GNU ld tried something similar with --omagic https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=e4897a3288f37d5f69e8acd256a6e83e607fe8d8 Reviewed By: tejohnson, psmith Differential Revision: https://reviews.llvm.org/D79371
2020-05-05 05:42:36 +08:00
Breaking changes
----------------
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* ...
[ELF] Add convenience TableGen classes to enforce two dashes for options not supported by GNU ld Announced on https://lists.llvm.org/pipermail/llvm-dev/2020-May/141416.html For many options, we have to support either one or two dash to be compatible with GNU ld. For newer and lld specific options, we can enforce strict double dashes. Affected options: * --thinlto-* * --lto-* * --shuffle-sections= This patch does not change `-plugin-opt=*` because clang driver passes `-plugin-opt=*` and I don't intend to cause churn. In 2000, GNU ld tried something similar with --omagic https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=e4897a3288f37d5f69e8acd256a6e83e607fe8d8 Reviewed By: tejohnson, psmith Differential Revision: https://reviews.llvm.org/D79371
2020-05-05 05:42:36 +08:00
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COFF Improvements
-----------------
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* ...
[docs] Mention some notable feature in the release notes Differential Revision: https://reviews.llvm.org/D52908 llvm-svn: 343878
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MinGW Improvements
------------------
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* ...
[docs] Mention some notable feature in the release notes Differential Revision: https://reviews.llvm.org/D52908 llvm-svn: 343878
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MachO Improvements
------------------
* Item 1.
[WebAssembly] Initial support for shared objects (-shared) Based on the initial spec proposal: https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md The llvm/codegen side of this is still missing but I believe this change is still worth landing as an incremental step Differential Revision: https://reviews.llvm.org/D54249 llvm-svn: 346918
2018-11-15 08:37:21 +08:00
WebAssembly Improvements
------------------------