236362 2022-02-09 06:26:18 -0800 [Flatpak SDK] Add mold linker 2022-05-06 06:50:07 -0700 1 1 1 Unclassified WebKit Tools / Tests WebKit Local Build Unspecified Unspecified RESOLVED FIXED https://bugs.webkit.org/show_bug.cgi?id=235979 https://bugs.webkit.org/show_bug.cgi?id=240162 InRadar P2 Normal --- 1 aperez aperez aperez bugs-noreply clopez mcatanzaro pnormand svillar webkit-bug-importer oldest_to_newest 1839117 0 aperez 2022-02-09 06:26:18 -0800 I have it working locally and intend to do some benchmarks to see how much faster we can get debug (developer) builds by switching to ld.lld or ld.mold For those who may not yet know about it, you can learn about Mold here: https://github.com/rui314/mold While it is still missing a few features, the only important issue is that Mold does *not* support LTO at the moment: https://github.com/rui314/mold/issues/181 Other than this, Mold is perfectly usable today for complex projects like WebKit, and given that developers typically do not do LTO builds when working on the codebase, it may already be interesting to have it in the SDK for those. 1839119 1 451367 aperez 2022-02-09 06:38:11 -0800 Created attachment 451367 Patch 1839126 2 aperez 2022-02-09 07:11:37 -0800 To use Mold, either of these work, tested both with the WPE and GTK ports: GCC ≥ 12: % LDFLAGS=-fuse-ld=mold Tools/Scripts/build-webkit [...] GCC < 12: % LDFLAGS=-B/usr/lib/mold Tools/Scripts/build-webkit [...] Clang: % LDFLAGS=-fuse-ld=mold CC=clang CXX=clang++ Tools/Scripts/build-webkit [...] Adding “-flto” to {C,CXX,LD}FLAGS will result in linker failures due to the missing support for LTO in Mold. 1839146 3 451367 pnormand 2022-02-09 07:34:54 -0800 Comment on attachment 451367 Patch View in context: https://bugs.webkit.org/attachment.cgi?id=451367&action=review > Tools/buildstream/elements/sdk/mold.bst:12 > +- kind: tar > + url: https://github.com/rui314/mold/archive/refs/tags/v1.0.3.tar.gz We usually track git tags instead of release tarballs, at least for projects hosted github. Any special reason to do it differently here? 1839149 4 aperez 2022-02-09 07:39:08 -0800 (In reply to Philippe Normand from comment #3) > Comment on attachment 451367 [details] > Patch > > View in context: > https://bugs.webkit.org/attachment.cgi?id=451367&action=review > > > Tools/buildstream/elements/sdk/mold.bst:12 > > +- kind: tar > > + url: https://github.com/rui314/mold/archive/refs/tags/v1.0.3.tar.gz > > We usually track git tags instead of release tarballs, at least for projects > hosted github. Any special reason to do it differently here? Fetching Git repositories when there are tarballs available is wasteful as it uses more bandwidth and local disk space. It may seem moot, but it all adds up. 1839383 5 aperez 2022-02-09 13:25:20 -0800 I had a chat with Philippe and it turns out that referencing Git commits is what is usually done in the Freedesktop SDK sources — I still wonder why it's done like that, but for consistency I will change the patch to use a Git ref. 1839424 6 aperez 2022-02-09 15:05:38 -0800 (In reply to Adrian Perez from comment #2) > GCC < 12: > % LDFLAGS=-B/usr/lib/mold Tools/Scripts/build-webkit [...] This is actually: % LDFLAGS=-B/usr/libexec/mold Tools/Scripts/build-webkit [...] (In Arch Linux there is no “libexec/” but the Flatpak SDK has it, that's where my confusion came from.) 1839598 7 aperez 2022-02-10 04:31:33 -0800 I did seven runs with each linker, took out the outliers, and got the following results: Linker | Times | Avg. | Speedup -------+---------------------+-------+------------------ BFD | 393 403 273 267 274 | 322.0 | 1.00x (baseline) Mold | 117 106 99 107 105 | 106.8 | 3.01x Gold | 81 116 82 79 82 | 88.0 | 3.66x LLD | 106 70 76 70 72 | 78.8 | 4.09x For each linker, I first removed the build directory, then ran the build command to have all the object files built, and for each run removed “bin/*” and “lib/*.so*” before to make sure that the time differences measured are caused by switching the linker. Commands used for each were: LDFLAGS=-B/usr/libexec/mold NUMBER_OF_PROCESSORS=33 \ ./Tools/Scripts/build-webkit --gtk --debug --cmakeargs='-DUSE_LD_LLD=OFF' LDFLAGS=-fuse-ld=bfd NUMBER_OF_PROCESSORS=33 \ ./Tools/Scripts/build-webkit --gtk --debug --cmakeargs='-DUSE_LD_LLD=OFF' LDFLAGS=-fuse-ld=gold NUMBER_OF_PROCESSORS=33 \ ./Tools/Scripts/build-webkit --gtk --debug --cmakeargs='-DUSE_LD_LLD=OFF' LDFLAGS=-fuse-ld=lld NUMBER_OF_PROCESSORS=33 \ ./Tools/Scripts/build-webkit --gtk --debug --cmakeargs='-DUSE_LD_LLD=ON' This was done using the Flatpak SDK, which means the compiler was GCC 11.2.0 -- hence the need to use the -B<path> flag to make it use Mold. I don't know if this might be the cause of the Mold not being faster but I would not expect that the compiler driver needing to do program lookups in a different way would cause a slowdown; but it could as well be an issue in Mold itself. It would be interesting to use Clang as the compiler (and hence as driver for the linking) so all linkers can be chosen in the same way using the -fuse-ld=<name> flag. Given these numbers, switching from the BFD linker to LLD by default for debug/development builds should be a no brainer. We have bug #235979 for that =) 1839614 8 451521 aperez 2022-02-10 05:52:19 -0800 Created attachment 451521 Patch v2 1840513 9 aperez 2022-02-11 13:19:43 -0800 (In reply to Adrian Perez from comment #0) > While it is still missing a few features, the only important issue is > that Mold does *not* support LTO at the moment: > > https://github.com/rui314/mold/issues/181 Initial LTO support just landed earlier today: https://github.com/rui314/mold/commit/46995bcfc3e3113133620bf16445c5f13cd76a18 \o/ 1841651 10 pnormand 2022-02-15 04:09:53 -0800 Thanks! I can include this in the next SDK roll-out which I'm preparing already. 1841652 11 aperez 2022-02-15 04:11:25 -0800 (In reply to Philippe Normand from comment #10) > Thanks! I can include this in the next SDK roll-out which I'm preparing > already. Sounds good! 👍️ 1841655 12 ews-feeder 2022-02-15 04:32:41 -0800 Committed r289801 (247266@main): <https://commits.webkit.org/247266@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 451521. 1841657 13 webkit-bug-importer 2022-02-15 04:33:31 -0800 <rdar://problem/88958643> 451367 2022-02-09 06:38:11 -0800 2022-02-10 05:52:14 -0800 Patch bug-236362-20220209163810.patch text/plain 2707 aperez U3VidmVyc2lvbiBSZXZpc2lvbjogMjg5NDY1CmRpZmYgLS1naXQgYS9Ub29scy9idWlsZHN0cmVh bS9DaGFuZ2VMb2cgYi9Ub29scy9idWlsZHN0cmVhbS9DaGFuZ2VMb2cKaW5kZXggY2Q4ZGMzMjMx ZTAzMzA2ZTU4NTdlOTNmZjBjYzNkNjdkN2JhMzkxMC4uYjdmYTdjZDFmYjA2MzNkMGE2NGIzMThk ZTg3YzMwZjFlOWFiMDAwMiAxMDA2NDQKLS0tIGEvVG9vbHMvYnVpbGRzdHJlYW0vQ2hhbmdlTG9n CisrKyBiL1Rvb2xzL2J1aWxkc3RyZWFtL0NoYW5nZUxvZwpAQCAtMSwzICsxLDI5IEBACisyMDIy LTAyLTA5ICBBZHJpYW4gUGVyZXogZGUgQ2FzdHJvICA8YXBlcmV6QGlnYWxpYS5jb20+CisKKyAg ICAgICAgW0ZsYXRwYWsgU0RLXSBBZGQgbW9sZCBsaW5rZXIKKyAgICAgICAgaHR0cHM6Ly9idWdz LndlYmtpdC5vcmcvc2hvd19idWcuY2dpP2lkPTIzNjM2MgorCisgICAgICAgIFJldmlld2VkIGJ5 IE5PQk9EWSAoT09QUyEpLgorCisgICAgICAgIFRoZSBNb2xkIGxpbmtlciBjbGFpbXMgdG8gYmUg 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