http://d.puremagic.com/issues/show_bug.cgi?id=5278


dawg@dawgfoto.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dawg@dawgfoto.de


--- Comment #20 from dawg@dawgfoto.de 2011-12-18 23:12:56 PST ---
The core issue is that your gcc is linking PIE by default but PIC support for dmd still has some bug and probably would need more that -fPIC to support PIE. Currently you should pass -fno-pie to gcc for linking.

Please help to find out why --export-dynamic is involved.
Does it trigger alter the PIE behavior?
What's the backtrace of your segfault core dumps?
Please list any linker warnings you get
(-Wl,--verbose for gcc or -L--verbose for dmd).

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--- Comment #21 from Chad Joan <chadjoan@gmail.com> 2012-01-20 19:32:30 PST ---
(In reply to comment #20)
> The core issue is that your gcc is linking PIE by default but PIC support for dmd still has some bug and probably would need more that -fPIC to support PIE. Currently you should pass -fno-pie to gcc for linking.
> 
> Please help to find out why --export-dynamic is involved. Does it trigger alter the PIE behavior?

How do I find this out?

> What's the backtrace of your segfault core dumps?

Also, how do I find this out?
Running the program just makes it print "Segmentation fault"; there is no
backtrace for me to copy.  Maybe I am missing something (where would I find a
core dump for this?).

> Please list any linker warnings you get
> (-Wl,--verbose for gcc or -L--verbose for dmd).

Stock DMD v2.057
64-bit:
chad@Hugin /mnt/bulk/dprojects/helloD2 $ which dmd
/usr/local/share/dcompilers/dmd/linux/bin64/dmd

chad@Hugin /mnt/bulk/dprojects/helloD2 $ cat main.d
import std.stdio;

void main()
{
        writefln("hello world!");
}

Without -m32 it isn't able to compile my program: http://pastebin.com/GqP5JC3z

With -m32 it does, but segfaults: http://pastebin.com/hd5zEtD2

32-bit dmd:
chad@Hugin /mnt/bulk/dprojects/helloD2 $ which dmd
/usr/local/share/dcompilers/dmd/linux/bin32/dmd

Segfaults:
http://pastebin.com/d7miSKtH

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--- Comment #22 from dawg@dawgfoto.de 2012-01-21 22:50:46 PST ---
What's linker flags are passed by gcc if you use --export-dynamic vs. not using it?

dmd -c main
----------
gcc main.o -o main -m32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib64 -Xlinker --no-warn-search-mismatch -Xlinker --export-dynamic -lphobos2 -lpthread -lm -lrt -v
----------
vs.
----------
gcc main.o -o main -m32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib64 -Xlinker --no-warn-search-mismatch -lphobos2 -lpthread -lm -lrt -v
----------

Also did passing -fno-pie to gcc resolve your problems?

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--- Comment #23 from Chad Joan <chadjoan@gmail.com> 2012-01-22 09:28:48 PST ---
(In reply to comment #22)

Thank you for clarifying.

> What's linker flags are passed by gcc if you use --export-dynamic vs. not using it?
> 
> dmd -c main
> ----------
> gcc main.o -o main -m32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib64 -Xlinker --no-warn-search-mismatch -Xlinker --export-dynamic -lphobos2 -lpthread -lm -lrt -v

http://pastebin.com/BD52Kkp2

> ----------
> vs.
> ----------
> gcc main.o -o main -m32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib32 -Xlinker -L/usr/local/share/dcompilers/dmd/linux/bin32/../lib64 -Xlinker --no-warn-search-mismatch -lphobos2 -lpthread -lm -lrt -v

(no segfault)
http://pastebin.com/0yA29by1

> ----------
> 
> Also did passing -fno-pie to gcc resolve your problems?

Yes.
http://pastebin.com/yLQacSuf

Those were all 32-bit.

I suppose the natural next thing to try is 64-bit:
http://pastebin.com/utYgp7YA
And yep, -fno-pie makes it run.

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--- Comment #24 from Chad Joan <chadjoan@gmail.com> 2012-01-22 09:41:55 PST ---
(In reply to comment #22)

Additional info:
I can get basic stack traces now.  Yay!  And I don't have to use paxctl -m
anymore.  Also yay!
http://pastebin.com/tt784wYr

More line numbers in the stack trace would be nice though.

I suspect this -fno-pie thing will make shared libraries impossible on my setup until this gets resolved though, right?

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dawg@dawgfoto.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


--- Comment #25 from dawg@dawgfoto.de 2012-01-22 16:57:07 PST ---
>I suspect this -fno-pie thing will make shared libraries impossible on my setup until this gets resolved though, right?
No, it doesn't.
PIE simply means randomized address space for the executable.
I do even think that PIE should work out of the box if you
compile phobos and you executables with -fPIC.

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--- Comment #26 from Chad Joan <chadjoan@gmail.com> 2012-01-25 21:05:07 PST ---
(In reply to comment #25)
> >I suspect this -fno-pie thing will make shared libraries impossible on my setup until this gets resolved though, right?
> No, it doesn't.
> PIE simply means randomized address space for the executable.
> I do even think that PIE should work out of the box if you
> compile phobos and you executables with -fPIC.

Oh, my bad.  I confused PIE with PIC.

So, just to be clear, -fpie is not passed by default on most systems, but it is on mine (a feature of the hardened GCC).  DMD's binary release of phobos is then compiled WITHOUT -fpie because that's the usual course of things, thus causing it to complain when I link it with something that compiles WITH -fpie.

Is there any chance that -fno-pie could make it into the list of things DMD passes to GCC by default?

Assuming I understand this all correctly, then other systems won't care if -fno-pie gets passed because they don't use PIE anyways.  On my system it will convert a dead-on-arrival binary release into something that works.

If someone still wanted to build with PIE then the ideal, I suppose, would be to have portage (the package manager) build everything from source, adding -fpie and -fPIC as necessary and adjusting the dmd.conf file to reflect it.

Also, is it even possible to get -fno-pie in there through dmd.conf?

When I add -L-fno-pie in dmd.conf it adds "-Xlinker -fno-pie" instead of just "-fno-pie" to the GCC args and it seems to end up going to the wrong place. Then I get linker errors and stuff won't build: http://pastebin.com/wEcuyUqp

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Chad Joan <chadjoan@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


--- Comment #27 from Chad Joan <chadjoan@gmail.com> 2012-02-04 19:21:23 PST ---
I'm reopening this because DMD won't work on my system unless -fno-pie is passed to GCC by DMD itself.

I can't even fix this without recompiling DMD because if I add "-L-fno-pie" to dmd.conf then will put "-Xlinker" before that and GCC itself never sees the "-fno-pie".  (See my previous comment for more detail.)

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--- Comment #29 from Chad Joan <chadjoan@gmail.com> 2012-02-05 14:06:08 PST ---
(In reply to comment #28)
> Yeah, it's a limitation that dmd doesn't let you pass flags to gcc. It's a different bug though.
> 
> Have you actually tried to build PIE using dmd's -fPIC flag. You'd need to rebuild druntime and phobos with the fPIC too. I think PIE will work without further changes.

It seemed like it was working before, but I did it again with more rigor to try and confirm that all of the flags are what I think they are.  It didn't work too well.

Here's what happened:
druntime compile: http://pastebin.com/e5HjcVRb
phobos compile: http://pastebin.com/4uATCBt1
executable compile:

chad@Hugin /mnt/bulk/dprojects/helloD2 $ dmd -fPIC -c main.d
chad@Hugin /mnt/bulk/dprojects/helloD2 $ gcc main.o -o main -m32 -Xlinker
-L/usr/local/share/dcompilers/dmd/linux/bin/../lib -lphobos2 -lpthread -lm -lrt
-fPIC -pie
/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld:
warning: creating a DT_TEXTREL in object.
chad@Hugin /mnt/bulk/dprojects/helloD2 $ main
main: error while loading shared libraries: cannot make segment writable for
relocation: Permission denied
chad@Hugin /mnt/bulk/dprojects/helloD2 $ sudo paxctl -m main
chad@Hugin /mnt/bulk/dprojects/helloD2 $ main
Killed
chad@Hugin /mnt/bulk/dprojects/helloD2 $

If I did something wrong, please let me know a better way.


What's the issue# for the bug preventing DMD from forwarding arguments to GCC? It's actually really easy to write a patch for that.  In fact, I did it so that I could continue working on my system.  Otherwise there is no way for me to have DMD work on my system without hardcoding "-fno-pie" into dmd/src/link.c and compiling from git.

Now, this is probably the wrong place for it, and I could stand to improve it
slightly and make sure it works off of the latest git sources (I was working
offline with this), but here is the patch for adding a -cflags parameter in
DMD, just in case anyone wants it:
http://pastebin.com/U6cTmryQ

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Chad Joan <chadjoan@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |7678
           Severity|blocker                     |major


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