1746462 - Give the mold linker a spin

Status: RESOLVED FIXED

(Firefox Build System :: Toolchains, task)

Description

[Gabriele Svelto [:gsvelto]]

The mold linker just hit its 1.0 release.

It claims to be able to link Firefox and be significantly faster than lld. Filing this to remind me to give it a spin.

Comment 1

[Sylvestre Ledru [:Sylvestre]]

Attachment: Bug 1746462 - add support for --enable-linker=mold on linux. r=glandium

Comment 2

[Mike Hommey [:glandium]]

FWIW, linking libxul on my machine with gold vs. lld vs. mold with the same flags:

limited to  gold     lld   mold
  1 core    15.99s   9.25s 7.38s
  2 cores  unchanged 5.49s 3.88s
  4 cores  unchanged 4.44s 2.67s
  6 cores  unchanged 3.74s 2.09s
  8 cores  unchanged 3.58s 1.76s
 unlimited unchanged 2.27s 0.73s

With hints from https://maskray.me/blog/2021-12-19-why-isnt-ld.lld-faster :

                          no build-id   no build-id
limited to  lld   mold    lld   mold    lld -Wl,-O0
  1 core    9.25s 7.38s   6.44s 6.35s   3.41s
  2 cores   5.49s 3.88s   4.09s 3.40s   2.32s
  4 cores   4.44s 2.67s   3.53s 2.36s   2.10s
  6 cores   3.74s 2.09s   3.08s 1.89s   1.94s
  8 cores   3.58s 1.76s   2.92s 1.55s   1.88s
 unlimited  2.27s 0.73s   2.12s 0.70s   1.65s

Comment 3

[Amit Prakash Ambasta]

Oddly enough, mold linker fails while building libxul.so

/usr/lib/llvm/13/bin/x86_64-pc-linux-gnu-clang++ -std=gnu++17 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fstack-protector-strong -fstack-clash-protection -Qunused-arguments -Qunused-arguments -Wall -Wbitfield-enum-conversion -Wdeprecated-this-capture -Wempty-body -Wformat-type-confusion -Wignored-qualifiers -Wpointer-arith -Wshadow-field-in-constructor-modified -Wsign-compare -Wtype-limits -Wno-error=tautological-type-limit-compare -Wunreachable-code -Wunreachable-code-return -Wunused-but-set-parameter -Wno-invalid-offsetof -Wclass-varargs -Wempty-init-stmt -Wfloat-overflow-conversion -Wfloat-zero-conversion -Wloop-analysis -Wno-range-loop-analysis -Wc++2a-compat -Wcomma -Wenum-compare-conditional -Wimplicit-fallthrough -Wstring-conversion -Wno-inline-new-delete -Wno-error=deprecated-declarations -Wno-error=array-bounds -Wno-error=backend-plugin -Wno-error=free-nonheap-object -Wno-error=return-std-move -Wno-error=atomic-alignment -Wno-error=deprecated-copy -Wformat -Wformat-security -Wno-gnu-zero-variadic-macro-arguments -Wno-psabi -Wno-unknown-warning-option -fno-sized-deallocation -fno-aligned-new -march=native -pipe -fno-stack-protector -fno-exceptions -fPIC -fno-rtti -ffunction-sections -fdata-sections -fno-exceptions -fno-math-errno -pthread -pipe -O3 -fomit-frame-pointer -funwind-tables  -shared -Wl,-z,defs -Wl,--gc-sections -Wl,-h,libxul.so -o libxul.so /var/tmp/portage/www-client/firefox-98.0/work/firefox_build/toolkit/library/build/libxul_so.list  -flto=thin -Wl,-plugin-opt=-import-instr-limit=10 -Wl,-plugin-opt=-import-hot-multiplier=30 -lpthread -Wl,-O1 -Wl,--as-needed -Wl,--compress-debug-sections=zlib -Wl,-rpath=/usr/lib64/firefox,--enable-new-dtags -fuse-ld=mold -Wl,-z,noexecstack -Wl,-z,text -Wl,-z,relro -Wl,-z,nocopyreloc -Wl,-Bsymbolic-functions -fstack-protector-strong -fstack-clash-protection -Wl,-rpath-link,/var/tmp/portage/www-client/firefox-98.0/work/firefox_build/dist/bin -Wl,-rpath-link,/usr/lib  ../../../js/src/build/libjs_static.a /var/tmp/portage/www-client/firefox-98.0/work/firefox_build/86_64-unknown-linux-gnu/release/libgkrust.a ../../../security/sandbox/linux/libmozsandbox.so ../../../config/external/lgpllibs/liblgpllibs.so ../../../config/external/sqlite/libmozsqlite3.so ../../../widget/gtk/mozgtk/libmozgtk.so ../../../widget/gtk/mozwayland/libmozwayland.so -Wl,--version-script,symverscript  -licui18n -licuuc -licudata -lasound -lrt -lm -ldl -lpthread -lc -lffi -lplds4 -lplc4 -lnspr4 -lz -lssl3 -lsmime3 -lnss3 -lnssutil3 -lfreetype -lfontconfig -lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -lharfbuzz -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lgraphite2 -lwebpdemux -lwebp -levent -lvpx -lpixman-1 -ldbus-glib-1 -ldbus-1

Error

mold: fatal: /var/tmp/portage/www-client/firefox-98.0/work/firefox_build/toolkit/library/build/libxul_so.list:1022: INPUT("../../../media/libaom/entropy.o")
                                                                                                                   ^ library not found: ../../../media/libaom/entropy.o

though ../../../media/libaom/entropy.o exists relative to cwd (where clang is invoked from)

Comment 4

[Amit Prakash Ambasta]

Resolve the aforementioned error. Was due to insufficient ulimits. Though PGO+LTO build still fails due to relocation errors

relocation R_X86_64_GOTPCREL against Gecko_ReleaseAtom out of range

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/27ad8fddd96d
add support for --enable-linker=mold on linux. r=glandium

Comment 6

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/27ad8fddd96d