September 28, 2016
On Monday, 26 September 2016 at 18:52:04 UTC, Joseph Rushton Wakeling wrote:
> Hello all,
>
> I've run into a nasty little issue with `std.net.curl` and ldc v1.0.0.  If I build v1.0.0 freshly from source, and then use it to compile the following tiny program:
>
> ////////////////////////////////////////////////
>
> void main ()
> {
>     import std.net.curl : get;
>     auto website = "http://dlang.org/".get;
> }
>
> ////////////////////////////////////////////////
>
> ... the program compiles correctly, but when I run it, I get a segfault.  A stacktrace is given here:
> https://forum.dlang.org/post/cxfrbiwccxdnmrkuufwe@forum.dlang.org
>
> This doesn't however occur if I build my program with the pre-built ldc v1.0.0 downloadable from GitHub.
>
> I'm guessing this is in some way related to the fact that as of ldc v1.0.0, libcurl.so is dynamically loaded at runtime rather than being linked to phobos at build time.  So this makes me wonder: is there something extra required when building LDC that I might be missing?  I note that dmd now automatically links against libdl in order to support dynamic loading of libraries:
> https://github.com/dlang/dmd/commit/541d9b61cd1792535cd4c99c418b42273bb9baa5
>
> ... so could I be missing something similar when building LDC?
>
> I note that if I manually link in -ldl when compiling my program above, it makes no difference to the segfault.
>
> Can anyone advise what could be wrong?
>
> Thanks & best wishes,
>
>     -- Joe

I suggest you to try https://github.com/ikod/dlang-requests it's much better than curl
September 28, 2016
On Wednesday, 28 September 2016 at 06:23:48 UTC, Suliman wrote:
> I suggest you to try https://github.com/ikod/dlang-requests it's much better than curl

Thanks for the suggestion, but it doesn't address my problem in this case.  I'm not concerned about being able to perform an HTTP GET request per se, but about being able to guarantee that the LDC + libs that I build will appropriately build programs based on any part of the standard library.
October 15, 2016
On Tuesday, 27 September 2016 at 21:00:03 UTC, kinke wrote:
> On Tuesday, 27 September 2016 at 18:34:41 UTC, Joseph Rushton Wakeling wrote:
>> If I replace druntime with the pre-built one, then things work OK with the built curl-using program.  Switching out phobos makes no difference.
>
> Oh this may make things clearer. druntime features C parts, so the pre-built one and yours probably differ in the used C(++) runtime; the malloc issue also points in this direction. As we seem to be using libstdc++, are you sure you're using that one too?

I've come back to this after a little while of not being able to work on it.  Anyway, a few questions.

First, the build scripts for LDC:
https://github.com/ldc-developers/ldc-scripts/tree/master/ldc2-packaging

There are 3 noticeable things about them:

(i) a backported g++-4.9 is used (the default gcc/g++ version on Ubuntu 16.04 is 5.4)

(ii) LLVM is built from source

(iii) the build script uses two cmake config flags related to the choice of standard library:

        -DCMAKE_EXE_LINKER_FLAGS='-stdlib=libc++'
        -DCMAKE_EXE_LINKER_FLAGS='-static-libstdc++

My own builds fail for LDC 1.0.0 if I use these exact cmake flags, because they are not recognized as valid flags by LDC itself.  Using instead:

        -DCMAKE_EXE_LINKER_FLAGS='-L-stdlib=libc++'
        -DCMAKE_EXE_LINKER_FLAGS='-L-static-libstdc++

... builds, but makes no difference.

So, first, can I confirm that these scripts are really used as-is to build LDC 1.0.0 and later LDC versions?

Second, since I use Ubuntu 16.04's native ldc 0.17.1 package as the D compiler to build ldc 1.0.0, how is the need for an existing D compiler dealt with via LDC's own build scripts?  Is there an automated bootstrapping process?

Third, is it possible that the use of a pre-built LLVM could be affecting things?  Are there parts of LLVM used in LDC's druntime, particularly related to the GC?

Fourth, are there any known issues related to the libc/libstdc++ version and druntime?  Is there a reason why you didn't backport gcc 5 for building LDC?

Thanks & best wishes,

    -- Joe
October 15, 2016
On Saturday, 15 October 2016 at 19:22:42 UTC, Joseph Rushton Wakeling wrote:
> Third, is it possible that the use of a pre-built LLVM could be affecting things?  Are there parts of LLVM used in LDC's druntime, particularly related to the GC?

It shouldn't affect druntime directly any more than any other code (i.e. only through any potential codegen issues). The reason why we build LLVM from source is just one of reproducibility – several years ago now, we had seen a number of issues with broken distro packages, and it seemed prudent to build the binary packages with something entirely under our control.

> Fourth, are there any known issues related to the libc/libstdc++ version and druntime?  Is there a reason why you didn't backport gcc 5 for building LDC?

I believe it was simply the latest available version at the time, or maybe the oldest one required by LLVM (after switching to C++11, etc.). For the binary packages, the main goal is maximum compatibility, so we build on an old Ubuntu version – although, of course, these issues have been somewhat alleviated by linking glibc statically now.

There are no known issues with particular runtime versions, and if there were, we would try to work around them as well as possible.

 — David
October 15, 2016
On Monday, 26 September 2016 at 19:49:46 UTC, Joseph Rushton Wakeling wrote:
> On Monday, 26 September 2016 at 19:20:04 UTC, Joseph Rushton Wakeling wrote:
>> Thanks!  I notice that on Linux you use a -DCMAKE_EXE_LINKER_FLAGS='-static-libstdc++' that I'm not using.  I'll give that a try.
>
> Hmm, makes no apparent difference :-(

That's not surprising – it only causes the LDC executable itself to be linked statically, which shouldn't affect code generation. (Then again, the whole bug is rather strange to begin with, so it's good to have that ruled out.)

 — David
October 15, 2016
On Saturday, 15 October 2016 at 20:52:05 UTC, David Nadlinger wrote:
> That's not surprising – it only causes the LDC executable itself to be linked statically, which shouldn't affect code generation. (Then again, the whole bug is rather strange to begin with, so it's good to have that ruled out.)

Yes, I wasn't expecting it to make a difference either, but I thought I'd try.  I wondered if the `-stdlib=libstdc++` option might also make a difference but again, doesn't seem to (which again, I'm ultimately not too surprised by, since I would imagine that on any Debian-based system, libstdc++6 just dynamically links against libc6 for the C standard library parts.

I guess I could have a go at building using g++-4.9, which requires a few extra cmake flags to account for the naming of the GCC executable:

    -DCMAKE_C_COMPILER=gcc-4.9
    -DCMAKE_CXX_COMPILER=g++-4.9

but that runs into a problem related to the build scripts that looks like it assumes that the GCC executable will always be called `gcc`:

make -j4
Scanning dependencies of target gen_gccbuiltins
Scanning dependencies of target FileCheck
Scanning dependencies of target LDMD_CXX_LIB
[  0%] Generating ddmd/idgen
[  0%] Building CXX object CMakeFiles/gen_gccbuiltins.dir/utils/gen_gccbuiltins.cpp.o
[  0%] Building CXX object CMakeFiles/LDMD_CXX_LIB.dir/driver/exe_path.cpp.o
[  0%] Building CXX object CMakeFiles/FileCheck.dir/utils/FileCheck-3.8.cpp.o
Error: failed to locate gcc
CMakeFiles/LDCShared.dir/build.make:68: recipe for target 'ddmd/idgen' failed
make[2]: *** [ddmd/idgen] Error 1
CMakeFiles/Makefile2:141: recipe for target 'CMakeFiles/LDCShared.dir/all' failed
make[1]: *** [CMakeFiles/LDCShared.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
October 15, 2016
On Saturday, 15 October 2016 at 22:09:35 UTC, Joseph Rushton Wakeling wrote:
> but that runs into a problem related to the build scripts that looks like it assumes that the GCC executable will always be called `gcc`:

I don't think that would be the build scripts, but the host D compiler trying to link the executable.

 — David
October 15, 2016
On Saturday, 15 October 2016 at 22:20:12 UTC, David Nadlinger wrote:
> I don't think that would be the build scripts, but the host D compiler trying to link the executable.

Oh, damn, of course.  I got fooled by the fact that it showed up right after a bunch of stuff related to CMakeFiles.

Is there a convenient cmake flag to pass some flags to the D compiler so that I can specify the GCC executable?
October 15, 2016
On Saturday, 15 October 2016 at 23:31:33 UTC, Joseph Rushton Wakeling wrote:
> Is there a convenient cmake flag to pass some flags to the D compiler so that I can specify the GCC executable?

IIRC, you can set either D_COMPILER or the DMD environment variable.

 — David
October 16, 2016
On Saturday, 15 October 2016 at 23:34:41 UTC, David Nadlinger wrote:
> IIRC, you can set either D_COMPILER or the DMD environment variable.

That unfortunately runs straight into a problem that I think we already encountered earlier: because the build scripts check for the existence of the D compiler, it finds that "ldc -gcc=gcc-4.9" does not exist :-\

There's DDMD_DFLAGS, which I tried setting with -DDDMD_DFLAGS=-gcc=gcc-4.9 and -DDDMD_DFLAGS="-gcc=gcc-4.9", and neither works; the cmake call generates output:

    -- Found D compiler /usr/bin/ldmd2, with default flags ''
    -- D compiler version: LDC - the LLVM D compiler (0.17.1)

... followed by the same old 'gcc not found' error, so it's somehow not being picked up.  I'd suspect that is down to these lines in CMakeLists.txt:

    set(DDMD_DFLAGS "-wi")
    set(DDMD_LFLAGS "")

which presumably override anything set by the command-line flags.

I tried tweaking the CMakeLists.txt file directly to set the -gcc=gcc-4.9 flag, and instead I get a linker error:

[  0%] Linking CXX executable bin/gen_gccbuiltins
CMakeFiles/gen_gccbuiltins.dir/utils/gen_gccbuiltins.cpp.o: In function `attributes(llvm::ListInit*)':
/home/joseph/code/D/ldc/utils/gen_gccbuiltins.cpp:91: undefined reference to `llvm::Record::getName() const'
CMakeFiles/gen_gccbuiltins.dir/utils/gen_gccbuiltins.cpp.o: In function `processRecord(llvm::raw_ostream&, llvm::Record&, std::string)':
/home/joseph/code/D/ldc/utils/gen_gccbuiltins.cpp:104: undefined reference to `llvm::Record::getValueAsString(llvm::StringRef) const'
/home/joseph/code/D/ldc/utils/gen_gccbuiltins.cpp:105: undefined reference to `llvm::Record::getName() const'
/home/joseph/code/D/ldc/utils/gen_gccbuiltins.cpp:125: undefined reference to `llvm::Record::getName() const'
collect2: error: ld returned 1 exit status

... which I would suspect is down to the prebuilt llvm-3.8 being built with g++ 5.4 and its corresponding libstdc++6 ... ?
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