fix Issue 17521 - -betterC programs should not link in Phobos by default

[WalterBright]

No description provided.

[WalterBright]

Consider the program:

import core.stdc.stdio;

extern (C) int main(char** argv, int argc) {
    printf("hello world\n");
    return 0;
}

compile on Win32 with -betterC, and the resulting executable is 23Kb! The non-better-C version is 194Kb.

[CyberShadow]

Is there a document which enumerates the effects of -betterC? May be worth starting keeping track of them.

[WalterBright]

I've been writing one. You're right, it is needed. But as betterC is a work in progress, I don't know yet what all it will need to do.

[JinShil]

I don't know yet what all it will need to do.

It's not necessary to document what it will do; only what it currently does.

[JinShil]

After pondering this a little, it occurred to me that DMD should never link in Phobos or druntime automatically. Rather, I think such dependencies should be specified on a platform-by-platform basis using a dmd.conf, linker script, or some other configuration file that is distributed with the toolchain's package.

[jpf91]

After pondering this a little, it occurred to me that DMD should never link in Phobos or druntime automatically. Rather, I think such dependencies should be specified on a platform-by-platform basis using a dmd.conf, linker script, or some other configuration file that is distributed with the toolchain's package.

👍

You need something like this anyway to handle druntime/phobos dependencies: Depending on the OS when linking an application with static libphobos/druntime you'll also have to explicitly link druntime or phobos dependencies (libdl, libz, on windows all the import libraries). Hardcoding this in the compiler is not a good idea.

In GDC we create a libgphobos.spec file when compiling phobos which contains all required dependencies. If libphobos is installed and the compiler can find this file it will link dependencies automatically:

cat /opt/gdc/lib64/libgphobos.spec 
#
# This spec file is read by gdc when linking.
# It is used to specify the libraries we need to link in, in the right
# order.
#

%rename lib liborig_gdc_renamed
*lib: %(liborig_gdc_renamed) -latomic -lm -lpthread  -ldl

phobos and druntime are still hardcoded here though. This is mostly to support simple shared/static library switching using --static-libphobos and --shared-libphobos. This requires bracketing -lphobos with special linker opts which seems difficult to do in GCC spec files.

[adamdruppe]

Does this mean that exceptions will NEVER work if you use the -betterC switch?

[WalterBright]

No. Just that the frame handler isn't by default on on FreeBSD.

[braddr]

IMHO, this is a good short term fix, but it's papering over the larger issue: way too much w/in phobos and druntime is dragged in when not needed or used. Andrei's work to kill off static this()'s will help a bunch. More investigation and effort needs to be put into making linking those libraries to be essentially free when no parts of them are used. IE, needing this flag is a sign that something somewhere is wrong and not addressing that head on is a problem.

[WalterBright]

I agree with you, @braddr , but this issue has been twisting around for 15 years with no progress and little interest. With the switch, we find out if this is a real thing or not, and we find out exactly what needs to be done.

[MartinNowak]

@WalterBright, you need to put the fix Issue 12345 reference into the commit message, not on github.
This also seems to fix most of Issue 11881 – -betterC switch suffers from bit rot, please add the issue as well.

[adamdruppe]

On Mon, Jun 26, 2017 at 10:31:14AM -0700, Martin Nowak wrote: We might want to remove the `_d_run_main` wrapper with `-betterC` as well.

Right now, it is generated, but not used, right? Cuz I've been playing with the -betterC patches (this one plus the two I did) and find it actually works quite well and I didn't even think about _d_run_main...

[MartinNowak]

Right now, it is generated, but not used, right?

I've updated the issue (https://issues.dlang.org/show_bug.cgi?id=11881#c18), just use an extern(C) main and the wrapper won't be generated.

[adamdruppe]

On Mon, Jun 26, 2017 at 10:42:00AM -0700, Martin Nowak wrote: I've updated the issue (https://issues.dlang.org/show_bug.cgi?id=11881#c18), just use an `extern(C) main` and the wrapper won't be generated.

oh good, then we're all set since with -betterC, you should use extern(C) main anyway.

[dlang-bot]

Thanks for your pull request, @WalterBright!

Bugzilla references

Fix	Bugzilla	Description
✓	11881	-betterC switch suffers from bit rot
✓	17521	-betterC programs should not link in Phobos runtime library by default

[WalterBright]

@MartinNowak seems like dlang-bot removed the auto-merge. We should immediately suppress insubordination by bots!

[MartinNowak]

@MartinNowak seems like dlang-bot removed the auto-merge. We should immediately suppress insubordination by bots!

GH had some delays processing push events (https://status.github.com/messages/2017-06-26), hence the bot got triggered after I added the label.

[wilzbach]

We should immediately suppress insubordination by bots!

In general, this is a feature to avoid allowing contributors without merge rights to sneak unapproved code into dlang repos. Our bot removes auto-merge if a new commit(s) gets added to a PR or a force-push to the PR branch has happened as these changes haven't been reviewed & approved yet. Unfortunately as @MartinNowak mentioned the GH API lead to this accident.