1384434 - (linker-lld) [meta] Link with LLD

Status: NEW

(Firefox Build System :: General, enhancement)

Description

[Sylvestre Ledru [:Sylvestre]]

On an old workstation (8 cpu, 32g of RAM and SSD)
linker libxul.so with LD:
real	0m22,170s
user	0m19,660s
sys	0m1,976s

with LLD:
real	0m3,147s
user	0m4,904s
sys	0m1,276s

I tried also with a more recent system and it is very similar: 0m17,772s / 0m2,745s

Comment 1

[Sylvestre Ledru [:Sylvestre]]

And we can now link without --disable-elf-hack!

Comment 2

[Kai Engert (:KaiE:)]

I didn't know about ldd, until :aceman told me about it today. Instead of 4 minutes, linking takes only 15 seconds on my system.

Is there a reason this isn't enabled automatically on platforms that support it?

Comment 3

[Nathan Froyd [:froydnj]]

(In reply to Kai Engert (:kaie:) from comment #2)

I didn't know about ldd, until :aceman told me about it today. Instead of 4 minutes, linking takes only 15 seconds on my system.

Is there a reason this isn't enabled automatically on platforms that support it?

It is supposed to be the default for developer builds, what does your mozconfig look like?

Comment 4

[Kai Engert (:KaiE:)]

Attachment: mozconf-without-lld

With this config, ld is used (not lld).

Comment 5

[Nathan Froyd [:froydnj]]

What does your $OBJDIR/config.log and $OBJDIR/config.status look like?

Comment 6

[Kai Engert (:KaiE:)]

Attachment: 1384434-logfiles.gz

Comment 7

[Kai Engert (:KaiE:)]

(In reply to Nathan Froyd [:froydnj] from comment #5)

What does your $OBJDIR/config.log and $OBJDIR/config.status look like?

attached

Comment 8

[Nathan Froyd [:froydnj]]

Hm, unfortunately the log doesn't contain enough information to debug just by looking at it. What does $HOME/.mozbuild/clang/bin/clang -std=gnu99 -Wl,--version -fuse-ld=lld say? That is what we should be running when we get here:

https://searchfox.org/mozilla-central/source/build/moz.configure/toolchain.configure#2014-2023

and apparently that check is failing.

Comment 9

[Kai Engert (:KaiE:)]

$ $HOME/.mozbuild/clang/bin/clang -std=gnu99 -Wl,--version -fuse-ld=lld
LLD 8.0.0 (compatible with GNU linkers)

Comment 10

[Kai Engert (:KaiE:)]

How can I print to the terminal from inside that script?
It seems to be python, but trying to use "print" results in errors.

It seems try_linker('lld') isn't executed.

Comment 11

[Nathan Froyd [:froydnj]]

(In reply to Kai Engert (:kaie:) from comment #10)

How can I print to the terminal from inside that script?
It seems to be python, but trying to use "print" results in errors.

It seems try_linker('lld') isn't executed.

You should be able to call log.info(...) to print.

Comment 12

[Kai Engert (:KaiE:)]

Thanks.

The reason try_linker('lld') isn't reached: developer_options is false.

Comment 13

[Nathan Froyd [:froydnj]]

(In reply to Kai Engert (:kaie:) from comment #12)

Thanks.

The reason try_linker('lld') isn't reached: developer_options is false.

Are you compiling a beta/release version of Thunderbird?

Comment 14

[Kai Engert (:KaiE:)]

My local build script, which I've been updating since many years, indeed contains two related symbol definitions:

export MOZILLA_OFFICIAL=1
export BUILD_OFFICIAL=1

If I remove those, then I get lld...

I don't remember why I had set those flags in the past, it was probably necessary for some local testing.

Comment 15

[Sylvestre Ledru [:Sylvestre]]

Out of topic but maybe we should show a warning at the end of the build
like
"please note that you are building an official version of Firefox. Options might be different".