Don't add phobos library dependences with -defaultlib=

[marler8997]

This PR depends on:
dlang/phobos#7021 [MERGED]
dlang/druntime#2619 [MERGED]
dlang/phobos#7050 [MERGED]
dlang/druntime#2625 [MERGED]

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[rainers]

Maybe -defaultlib=and -debuglib= should be modified to also not pass the system libraries to the linker? I guess they are added only to support linking in what might be used by phobos.

[JinShil]

What about moving the default libs to the command line in dmd.conf? https://github.com/dlang/installer/blob/master/create_dmd_release/extras/linux/dmd2/linux/bin64/dmd.conf

Then DMD doesn't need to hard-code all of the default libraries and it can be customized on a per-package/distribution/platform basis. If users don't want to link in any default libraries, they just use dmd -conf= to remove the effect of the dmd.conf file, or they can use a different whatever.conf file.

[marler8997]

I have use cases where I want to remove the default libraries without having to remove anything else that is currently in dmd.conf. I still want the default library paths provided in dmd.conf. I may still add the phobos2 library, probably via a pragma.

So whether or not the libraries we're hard-coded, or in dmd.conf, I would still need this flag, making that change orthogonal.

[marler8997]

@rainers I didn't know about -defaultlib=. Going to modify my PR per your suggestion.

[thewilsonator]

Still need a changelog entry anywhichway.

[codecov]

Codecov Report

Merging #9831 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #9831      +/-   ##
==========================================
+ Coverage   84.67%   84.68%   +<.01%     
==========================================
  Files         144      144              
  Lines       74524    74524              
==========================================
+ Hits        63102    63109       +7     
+ Misses      11422    11415       -7

Impacted Files	Coverage Δ
src/dmd/link.d	68.83% <100%> (+2.32%)	⬆️
src/dmd/mars.d	78.21% <0%> (+0.08%)	⬆️
src/dmd/glue.d	85.54% <0%> (+0.14%)	⬆️

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[marler8997]

I'm stumped on this one. Looks like on the linux platforms where the host/target are different bit-widths (Linux_32_64 and Linux_64_32), the linker is not finding the pthread library symbols.

https://auto-tester.puremagic.com/show-run.ghtml?projectid=1&runid=3663202&isPull=true

/home/braddr/sandbox/at-client/pull-3663202-Linux_32_64/dmd/generated/linux/release/32/dmd -m64 -fPIC -w -I../../src -I../../import -Isrc -defaultlib= -debuglib= -dip1000 -L-lpthread -L-lm -L/home/braddr/sandbox/at-client/pull-3663202-Linux_32_64/druntime/generated/linux/debug/64/libdruntime.a -g -debug -unittest -ofgenerated/linux/debug/64/unittest_assert src/unittest_assert.d
/home/braddr/sandbox/at-client/pull-3663202-Linux_32_64/druntime/generated/linux/debug/64/libdruntime.a(monitor__941_8c9.o): In function `_d_monitor_staticctor':
/home/braddr/sandbox/at-client/pull-3663202-Linux_32_64/druntime/src/rt/monitor_.d:158: undefined reference to `pthread_mutexattr_init'
...

Even though you can see we are explicitly providing -L-lpthread to DMD. Maybe there's a way to select different pthread libraries for your targest host? If anyone is familiar with this issue let me know.

[CyberShadow]

@wilzbach's suggestions for the changelog are still not applied and have been incorrectly marked as resolved by @thewilsonator.

[rainers]

Even though you can see we are explicitly providing -L-lpthread to DMD. Maybe there's a way to select different pthread libraries for your targest host? If anyone is familiar with this issue let me know.

ld is known to be picky about the order of libraries passed to it on the command line, i.e. -lpthread should better be after the libraries that reference symbols from libpthread.a. Can you add them to the end of the command line that invokes the linker?

[rainers]

From the top of the "build dmd" task: the failing Linux runs use GNU ld (GNU Binutils for Ubuntu) 2.26.1, while the successful ones use GNU ld version 2.25.1-31.base.66.amzn1. No idea what the difference is or whether it's just a coincidence.

[thewilsonator]

If you could convert the shell test to D, that would be great, the less of them we have the better.

[marler8997]

Yeah I'll convert the test to D.

[marler8997]

Ok bash test is now in D. Still need to figure out the linker issue when testing druntime though.

[PetarKirov]

Yep, it looks like you need to do more adjustments to the Makefiles in druntime/test/, but apart from that it looks promising.

[marler8997]

I've added a commit to put the core libs (pthread/m/dl/rt) at the end of the link command, but still getting the undefined reference errors in the linker...

[marler8997]

Cleaning up old PRs that aren't going anywhere.