[uClibc][MIPS32] Segfault when cross-compiling code using variadics

[rracariu]

Cross compiling the following code gives a segfault when targeting MIPS32.

import core.stdc.stdarg;

extern (C) int res(int a, ...)
{
    va_list args;
    va_start(args, a);

    int i;
    va_arg(args, i);
    va_arg(args, i);

    return i;
}

void main()
{
    import std.stdio;
    writeln("Res ", res(4, 56, 3));
}

The compiler debug:

ldc-openwrt-uclib-mips -v args.d
binary    /dlang/ldc-1.13.0/bin/ldc2
version   1.13.0 (DMD v2.083.1, LLVM 7.0.1)
config    /dlang/ldc-1.13.0/etc/ldc2.conf (mipsel-unknown-linux-uclibc)
predefs   LDC all D_Version2 assert D_ModuleInfo D_Exceptions D_TypeInfo MIPS MIPS32 MIPS_SoftFloat D_SoftFloat MIPS_O32 LittleEndian D_PIC linux Posix CRuntime_UClibc LDC_LLVM_700
parse     args
importall args
import    object        (/dlang/ldc-1.13.0/bin/../import/object.d)
import    core.internal.hash    (/dlang/ldc-1.13.0/bin/../import/core/internal/hash.d)
import    core.internal.traits  (/dlang/ldc-1.13.0/bin/../import/core/internal/traits.d)
import    core.internal.convert (/dlang/ldc-1.13.0/bin/../import/core/internal/convert.d)
import    core.stdc.stdarg      (/dlang/ldc-1.13.0/bin/../import/core/stdc/stdarg.d)
semantic  args
entry     main          args.d
semantic2 args
semantic3 args
import    std.stdio     (/dlang/ldc-1.13.0/bin/../import/std/stdio.d)
import    core.stdc.stddef      (/dlang/ldc-1.13.0/bin/../import/core/stdc/stddef.d)
import    core.stdc.stdio       (/dlang/ldc-1.13.0/bin/../import/core/stdc/stdio.d)
import    core.stdc.stdint      (/dlang/ldc-1.13.0/bin/../import/core/stdc/stdint.d)
import    core.stdc.config      (/dlang/ldc-1.13.0/bin/../import/core/stdc/config.d)
import    core.stdc.signal      (/dlang/ldc-1.13.0/bin/../import/core/stdc/signal.d)
import    core.stdc.wchar_      (/dlang/ldc-1.13.0/bin/../import/core/stdc/wchar_.d)
import    core.stdc.time        (/dlang/ldc-1.13.0/bin/../import/core/stdc/time.d)
import    core.sys.posix.sys.types      (/dlang/ldc-1.13.0/bin/../import/core/sys/posix/sys/types.d)
import    core.sys.posix.config (/dlang/ldc-1.13.0/bin/../import/core/sys/posix/config.d)
import    std.algorithm.mutation        (/dlang/ldc-1.13.0/bin/../import/std/algorithm/mutation.d)
import    std.traits    (/dlang/ldc-1.13.0/bin/../import/std/traits.d)
import    std.meta      (/dlang/ldc-1.13.0/bin/../import/std/meta.d)
import    std.functional        (/dlang/ldc-1.13.0/bin/../import/std/functional.d)
import    std.range.primitives  (/dlang/ldc-1.13.0/bin/../import/std/range/primitives.d)
import    std.typecons  (/dlang/ldc-1.13.0/bin/../import/std/typecons.d)
import    std.format    (/dlang/ldc-1.13.0/bin/../import/std/format.d)
import    core.vararg   (/dlang/ldc-1.13.0/bin/../import/core/vararg.d)
import    std.exception (/dlang/ldc-1.13.0/bin/../import/std/exception.d)
import    core.atomic   (/dlang/ldc-1.13.0/bin/../import/core/atomic.d)
import    ldc.intrinsics        (/dlang/ldc-1.13.0/bin/../import/ldc/intrinsics.di)
import    core.stdc.errno       (/dlang/ldc-1.13.0/bin/../import/core/stdc/errno.d)
import    std.utf       (/dlang/ldc-1.13.0/bin/../import/std/utf.d)
import    core.internal.string  (/dlang/ldc-1.13.0/bin/../import/core/internal/string.d)
import    std.algorithm.comparison      (/dlang/ldc-1.13.0/bin/../import/std/algorithm/comparison.d)
import    std.internal.attributes       (/dlang/ldc-1.13.0/bin/../import/std/internal/attributes.d)
import    std.algorithm.internal        (/dlang/ldc-1.13.0/bin/../import/std/algorithm/internal.d)
import    core.stdc.string      (/dlang/ldc-1.13.0/bin/../import/core/stdc/string.d)
import    std.conv      (/dlang/ldc-1.13.0/bin/../import/std/conv.d)
import    std.ascii     (/dlang/ldc-1.13.0/bin/../import/std/ascii.d)
code      args
/dlang/ldc/bin/ldc2(_ZN4llvm3sys15PrintStackTraceERNS_11raw_ostreamE+0x1a)[0x2a600da]
/dlang/ldc/bin/ldc2(_ZN4llvm3sys17RunSignalHandlersEv+0x35)[0x2a5e7d5]
/dlang/ldc/bin/ldc2[0x2a5e8ec]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7f75d89d1390]
/dlang/ldc/bin/ldc2(_ZNK10IrFunction11getLLVMFuncEv+0x0)[0xce9770]
/dlang/ldc/bin/ldc2(_Z17DtoDefineFunctionP15FuncDeclarationb+0x10a)[0xc7a57a]
/dlang/ldc/bin/ldc2[0xc6d833]
/dlang/ldc/bin/ldc2(_Z19Declaration_codegenP7DsymbolP7IRState+0x24)[0xc70444]
/dlang/ldc/bin/ldc2(_Z13codegenModuleP7IRStateP6Module+0xad)[0xc91abd]
/dlang/ldc/bin/ldc2(_ZN3ldc13CodeGenerator4emitEP6Module+0x99)[0xd3e969]
/dlang/ldc/bin/ldc2(_Z14codegenModulesR5ArrayIP6ModuleE+0x16e)[0xd13d7e]
/dlang/ldc/bin/ldc2(_Z13mars_mainBodyR5ArrayIPKcES3_+0x1410)[0xb33050]
/dlang/ldc/bin/ldc2(_Z7cppmainiPPc+0x1e41)[0xd12881]
/dlang/ldc/bin/ldc2(_D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ6runAllMFZv+0x50)[0x2b9e500]
/dlang/ldc/bin/ldc2(_d_run_main+0x1f6)[0x2b9e316]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f75d80e0830]
/dlang/ldc/bin/ldc2[0xa5f06f]
/usr/bin/ldc-openwrt-uclib-mips: line 4:  3295 Segmentation fault      (core dumped) ~/dlang/ldc/bin/ldc2 -mtriple=mipsel-unknown-linux-uclibc -mcpu=mips32r2 -float-abi=soft -gcc=mipsel-openwrt-linux-uclibc-gcc -linker=bfd -L=-L/dlang/ldc/lib-openwrt-uclib-mips -defaultlib=phobos2-ldc,druntime-ldc,drtsupp,:libatomic.a "$@"```

[kinke]

Cross-compiling shouldn't matter, it's just that core.stdc.stdarg defaults to the LLVM intrinsics for generic/unsupported architectures [which don't work anywhere IIRC ;), leading to LLVM assertions/crashes]. Specifically, there's (at least some) support for MIPS64, but not for MIPS32, e.g., here.

[rracariu]

Yeah, I remember testing this with an older LDC and it worked back then. I guess is a LLVM regression then?

[rracariu]

I was looking at this http://math-atlas.sourceforge.net/devel/assembly/mipsabi32.pdf and http://math-atlas.sourceforge.net/devel/assembly/mipsabi64.pdf and my understanding is the MIPS32 rules apply to MIPS64.

Am I correct?

[kinke]

Sorry, I don't have the time to look into this, but the logic is almost always the same for the 'simpler' architectures - read current value from pointer, then bump the pointer by type size + alignment padding, with alignment mostly being the size_t size. I'd try replacing MIPS64 in that file by a (new) MIPS_Any.

[rracariu]

OK, will try that later when I have access to the hardware to test. Having MIPS_Any compiles and links, just need to test this on the machine.
Thanks!

[rracariu]

Same code from MIPS64 works for MIPS32 on my HW.