[D-runtime] Bug 3150: requires changes to rt/lifetime.d

[Steve Schveighoffer]

I have a problem here.  If I change a function that returns a ulong to having it 
return an Array struct, the compiler expects the caller to push a reference to 
the return value on the stack, where it doesn't do that when returning a ulong.

Easily demonstrated with this code:

testlongtoarray2.d:
struct Array
{
    size_t length;
    ubyte* ptr;
}

extern(C) Array callme()
{
    Array d;
    d.length = 5;
    d.ptr = null;
    return d;
}

testlongtoarray.d:
extern(C) ulong callme();

void main()
{
    ulong x = callme();
}
[steves at steveslaptop testd]$ dmd -gc testlongtoarray*.d[steves at steveslaptop 
testd]$ gdb testlongtoarray2
GNU gdb (GDB) Fedora (6.8.50.20090302-40.fc11)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i586-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
(gdb) run
Starting program: /home/steves/testd/testlongtoarray2 
[Thread debugging using libthread_db enabled]

Program received signal SIGSEGV, Segmentation fault.
0x08049073 in callme (__HID1=0x180fc4) at testlongtoarray2.d:9  <------ note the 
hidden argument which is garbage!
9        Array d;
Missing separate debuginfos, use: debuginfo-install glibc-2.10.2-1.i686
(gdb) 

What's happening is that main is simply calling the function without pushing 
anything on the stack, but the implementation expects that the reference to the 
return value is on the stack.

Does this make any sense to anyone?  What should I do here?  I can't really 
change what the compiler expects the return value to be.

-Steve



----- Original Message ----
> From: Don Clugston <dclugston at googlemail.com>
> To: D-runtime at puremagic.com
> Sent: Fri, July 23, 2010 5:31:04 AM
> Subject: [D-runtime] Bug 3150: requires changes to rt/lifetime.d
> 
> Fixing this bug will be important for 64 bits:
> 3150 cast from dynamic array  to ulong is allowed
> 
> As discussed in the comments to that bug, a change is  required at two
> places in druntime, because druntime currently relies on the  compiler
> bug. I don't think it's particularly difficult, but I don't want to  do
> it myself. Can one of you guys take care of  it?
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