Hello, I don't understand why this code segfault on Linux/FreeBSD:

import std.stdio;
struct _Poc {
  this(this) { writeln("_Poc.this(this)"); }
}
void main() {
  _Poc[1] valueArray = [ _Poc() ];
  writeln(valueArray);
}

I've just defined the postblit function in _Poc to see how much it's invoked.
In my system, it's invoked 3 time after the segfault.
When the array is allocated on the heap, nothing happen.
So I guess it's because it's located on the stack but why?

regard.

On Monday, 1 June 2020 at 06:35:36 UTC, MaoKo wrote:
> Hello, I don't understand why this code segfault on Linux/FreeBSD:
>
> import std.stdio;
> struct _Poc {
>   this(this) { writeln("_Poc.this(this)"); }
> }
> void main() {
>   _Poc[1] valueArray = [ _Poc() ];
>   writeln(valueArray);
> }
>
> I've just defined the postblit function in _Poc to see how much it's invoked.
> In my system, it's invoked 3 time after the segfault.
> When the array is allocated on the heap, nothing happen.
> So I guess it's because it's located on the stack but why?
>
> regard.

I cannot help much, but I can say that problem is not about postblit. I tried running the code on https://run.dlang.io/. It works with LDC but not with DMD. Even though postblit is removed, it crashes because there may be a bug with DMD's writeln or there is something more that I missed too.

On Monday, 1 June 2020 at 06:35:36 UTC, MaoKo wrote:
> Hello, I don't understand why this code segfault on

Reduced to:

import std.stdio;

struct S {}

void main() {
  S[1] s;
  writeln(s);
}

On Monday, 1 June 2020 at 09:42:44 UTC, Boris Carvajal wrote:
> On Monday, 1 June 2020 at 06:35:36 UTC, MaoKo wrote:
>> Hello, I don't understand why this code segfault on
>
> Reduced to:
>
> import std.stdio;
>
> struct S {}
>
> void main() {
>   S[1] s;
>   writeln(s);
> }

This used to work up to dmd 2.084.1. It fails since 2.085.1. Please file a regression report at https://issues.dlang.org/enter_bug.cgi?product=D

— Bastiaan.

On Mon, Jun 01, 2020 at 01:53:09PM +0000, Bastiaan Veelo via Digitalmars-d-learn wrote:
> On Monday, 1 June 2020 at 09:42:44 UTC, Boris Carvajal wrote:
> > On Monday, 1 June 2020 at 06:35:36 UTC, MaoKo wrote:
> > > Hello, I don't understand why this code segfault on
> > 
> > Reduced to:
> > 
> > import std.stdio;
> > 
> > struct S {}
> > 
> > void main() {
> >   S[1] s;
> >   writeln(s);
> > }
> 
> This used to work up to dmd 2.084.1. It fails since 2.085.1. Please file a regression report at https://issues.dlang.org/enter_bug.cgi?product=D
[...]

Tracked the segfault to Phobos, writeUpToNextSpec():

	1216	            if (trailing[i] != '%') continue;

Apparently `trailing` has an invalid pointer.


T

-- 
They pretend to pay us, and we pretend to work. -- Russian saying

On Monday, 1 June 2020 at 14:53:43 UTC, H. S. Teoh wrote:
> On Mon, Jun 01, 2020 at 01:53:09PM +0000, Bastiaan Veelo via Digitalmars-d-learn wrote:
>> On Monday, 1 June 2020 at 09:42:44 UTC, Boris Carvajal wrote:
>> > On Monday, 1 June 2020 at 06:35:36 UTC, MaoKo wrote:
>> > > Hello, I don't understand why this code segfault on
>> > 
>> > Reduced to:
>> > 
>> > import std.stdio;
>> > 
>> > struct S {}
>> > 
>> > void main() {
>> >   S[1] s;
>> >   writeln(s);
>> > }
>> 
>> This used to work up to dmd 2.084.1. It fails since 2.085.1. Please file a regression report at https://issues.dlang.org/enter_bug.cgi?product=D
> [...]
>
> Tracked the segfault to Phobos, writeUpToNextSpec():
>
> 	1216	            if (trailing[i] != '%') continue;
>
> Apparently `trailing` has an invalid pointer.
>
>
> T

Possibly a backend bug (keyword "wrong code"), caused by either of [1] or [2]

[1] https://github.com/dlang/dmd/pull/9357
[2] https://github.com/dlang/dmd/pull/9623/files

On Mon, Jun 01, 2020 at 03:27:11PM +0000, Basile B. via Digitalmars-d-learn wrote: [...]
> Possibly a backend bug (keyword "wrong code"), caused by either of [1] or
> [2]
> 
> [1] https://github.com/dlang/dmd/pull/9357
> [2] https://github.com/dlang/dmd/pull/9623/files

Yeah, it looks like a backend bug.  The struct address was somehow either not loaded correctly, or not passed correctly (didn't look into more detail which case).

A regression should be filed for this, if not already.


T

-- 
It's amazing how careful choice of punctuation can leave you hanging:

On Monday, 1 June 2020 at 15:55:45 UTC, H. S. Teoh wrote:
> On Mon, Jun 01, 2020 at 03:27:11PM +0000, Basile B. via Digitalmars-d-learn wrote: [...]
>> Possibly a backend bug (keyword "wrong code"), caused by either of [1] or
>> [2]
>> 
>> [1] https://github.com/dlang/dmd/pull/9357
>> [2] https://github.com/dlang/dmd/pull/9623/files
>
> Yeah, it looks like a backend bug.  The struct address was somehow either not loaded correctly, or not passed correctly (didn't look into more detail which case).
>
> A regression should be filed for this, if not already.
>
>
> T

yeah done. culprit commit confirmed and reduced w/o phobos:

https://issues.dlang.org/show_bug.cgi?id=20890

On Monday, 1 June 2020 at 19:52:39 UTC, Basile B. wrote:
> On Monday, 1 June 2020 at 15:55:45 UTC, H. S. Teoh wrote:
>> On Mon, Jun 01, 2020 at 03:27:11PM +0000, Basile B. via Digitalmars-d-learn wrote: [...]
>>> Possibly a backend bug (keyword "wrong code"), caused by either of [1] or
>>> [2]
>>> 
>>> [1] https://github.com/dlang/dmd/pull/9357
>>> [2] https://github.com/dlang/dmd/pull/9623/files
>>
>> Yeah, it looks like a backend bug.  The struct address was somehow either not loaded correctly, or not passed correctly (didn't look into more detail which case).
>>
>> A regression should be filed for this, if not already.
>>
>>
>> T
>
> yeah done. culprit commit confirmed and reduced w/o phobos:
>
> https://issues.dlang.org/show_bug.cgi?id=20890

Ok cool. I hesitate to report an issue because the bug was too "simple".
This is a proof that dmd user use the GC a lot :).

On Tuesday, 2 June 2020 at 06:34:14 UTC, MaoKo wrote:
> On Monday, 1 June 2020 at 19:52:39 UTC, Basile B. wrote:
>> On Monday, 1 June 2020 at 15:55:45 UTC, H. S. Teoh wrote:
>>> On Mon, Jun 01, 2020 at 03:27:11PM +0000, Basile B. via Digitalmars-d-learn wrote: [...]
>>>> Possibly a backend bug (keyword "wrong code"), caused by either of [1] or
>>>> [2]
>>>> 
>>>> [1] https://github.com/dlang/dmd/pull/9357
>>>> [2] https://github.com/dlang/dmd/pull/9623/files
>>>
>>> Yeah, it looks like a backend bug.  The struct address was somehow either not loaded correctly, or not passed correctly (didn't look into more detail which case).
>>>
>>> A regression should be filed for this, if not already.
>>>
>>>
>>> T
>>
>> yeah done. culprit commit confirmed and reduced w/o phobos:
>>
>> https://issues.dlang.org/show_bug.cgi?id=20890
>
> Ok cool. I hesitate to report an issue because the bug was too "simple".
> This is a proof that dmd user use the GC a lot :).

Mmmmh I don't follow you, this has nothing to do with the GC. It's rather a problem with the backend (i.e the translation to an IR andthe generation of byte code)

Anyway someone already pushed a fix so next point release (~1 or 2 weeks) will not produce invalid code for the case you've found.