Re: union/toString: crash/segfault: What's happening here?
On Fri, Jan 12, 2018 at 10:49:45AM -0800, H. S. Teoh via Digitalmars-d-learn wrote: > On Fri, Jan 12, 2018 at 11:09:47AM +, kdevel via Digitalmars-d-learn > wrote: > [...] [...] > > https://issues.dlang.org/show_bug.cgi?id=18232 > > Yep, definitely a codegen bug. Apparently, local variables in union > member functions aren't initialized to .init as they should be. [...] Fix: https://github.com/dlang/dmd/pull/7687 Temporary workaround: explicitly initialize your local variables in union member functions. T -- Life begins when you can spend your spare time programming instead of watching television. -- Cal Keegan
Re: union/toString: crash/segfault: What's happening here?
On Fri, Jan 12, 2018 at 11:09:47AM +, kdevel via Digitalmars-d-learn wrote: [...] > On Friday, 12 January 2018 at 02:16:39 UTC, Adam D. Ruppe wrote: [...] > > I'd file this as a compiler codegen bug. > > https://issues.dlang.org/show_bug.cgi?id=18232 Yep, definitely a codegen bug. Apparently, local variables in union member functions aren't initialized to .init as they should be. Digging into the compiler code right now to see if I can find where the problem is... T -- Only boring people get bored. -- JM
Re: union/toString: crash/segfault: What's happening here?
Thanks for the quick answer! On Friday, 12 January 2018 at 02:16:39 UTC, Adam D. Ruppe wrote: On Friday, 12 January 2018 at 00:54:03 UTC, kdevel wrote: $ dmd crash.d $ ./crash Nicholas Wilson is right that you can use = "" to work around it, but with strings, null is supposed to behave the same way. And this gives different (each wrong) behavior on -m32 vs -m64, which leads me to believe you actually found a compiler bug. dmd -O crash even produces a binary which segfaults on my machine. Calling u.toString directly also leads to random spam, which means it isn't even the library. I'd file this as a compiler codegen bug. https://issues.dlang.org/show_bug.cgi?id=18232
Re: union/toString: crash/segfault: What's happening here?
On Friday, 12 January 2018 at 00:54:03 UTC, kdevel wrote: $ dmd crash.d $ ./crash Nicholas Wilson is right that you can use = "" to work around it, but with strings, null is supposed to behave the same way. And this gives different (each wrong) behavior on -m32 vs -m64, which leads me to believe you actually found a compiler bug. Calling u.toString directly also leads to random spam, which means it isn't even the library. I'd file this as a compiler codegen bug.
Re: union/toString: crash/segfault: What's happening here?
On 01/12/2018 02:45 AM, Nicholas Wilson wrote:
because you don't initialise `s` in
string toString ()
{
string s;
return s;
}
so it defaults to `string s = null;` thus giving a segfault.
try `string s = "";` instead.
A null string is a perfectly fine empty string. Printing it does not
lead to a segfault. And the thrown error is not a segfault.
Actually, the problem seems to be that s is not default initialized.
It's garbage. And garbage usually isn't a proper string, so writeln
fails. Looks like a compiler bug.
Re: union/toString: crash/segfault: What's happening here?
On Friday, 12 January 2018 at 01:45:37 UTC, Nicholas Wilson wrote: so it defaults to `string s = null;` thus giving a segfault. null and "" are basically the same for strings. that's not the problem.
Re: union/toString: crash/segfault: What's happening here?
On Friday, 12 January 2018 at 00:54:03 UTC, kdevel wrote:
crash.d
```
import std.stdio;
union U {
float f;
int i;
string toString ()
{
string s;
return s;
}
}
void main ()
{
U u;
writeln (u);
}
```
$ dmd crash.d
$ ./crash
because you don't initialise `s` in
string toString ()
{
string s;
return s;
}
so it defaults to `string s = null;` thus giving a segfault.
try `string s = "";` instead.
union/toString: crash/segfault: What's happening here?
crash.d
```
import std.stdio;
union U {
float f;
int i;
string toString ()
{
string s;
return s;
}
}
void main ()
{
U u;
writeln (u);
}
```
$ dmd crash.d
$ ./crash
std.exception.ErrnoException@/.../dmd2/linux/bin64/../../src/phobos/std/stdio.d(2776):
(Bad address)
??:? @safe int std.exception.errnoEnforce!(int,
"/.../dmd2/linux/bin64/../../src/phobos/std/stdio.d",
2776uL).errnoEnforce(int, lazy immutable(char)[]) [0x43f20a]
??:? @safe void
std.stdio.File.LockingTextWriter.put!(immutable(char)[]).put(immutable(char)[]) [0x4422a7]
??:? @safe void
std.range.primitives.doPut!(std.stdio.File.LockingTextWriter,
immutable(char)[]).doPut(ref std.stdio.File.LockingTextWriter,
ref immutable(char)[]) [0x44224b]
??:? @safe void
std.range.primitives.put!(std.stdio.File.LockingTextWriter,
immutable(char)[]).put(ref std.stdio.File.LockingTextWriter,
immutable(char)[]) [0x44222b]
??:? void
std.format.formatObject!(std.stdio.File.LockingTextWriter,
crash.U, char).formatObject(ref std.stdio.File.LockingTextWriter,
ref crash.U, ref const(std.format.FormatSpec!(char).FormatSpec))
[0x44220a]
??:? void
std.format.formatValue!(std.stdio.File.LockingTextWriter,
crash.U, char).formatValue(ref std.stdio.File.LockingTextWriter,
ref crash.U, ref const(std.format.FormatSpec!(char).FormatSpec))
[0x44219d]
??:? uint
std.format.formattedWrite!(std.stdio.File.LockingTextWriter,
char, crash.U).formattedWrite(ref
std.stdio.File.LockingTextWriter, const(char[]), crash.U)
[0x43e703]
??:? void std.stdio.File.write!(crash.U, char).write(crash.U,
char) [0x43e3f5]
??:? void std.stdio.writeln!(crash.U).writeln(crash.U) [0x43e389]
??:? _Dmain [0x43e344]
