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digitalmars.D.bugs - [Issue 8832] New: Segfault when accessing range returned by function that has delegate referencing local variables

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8832

           Summary: Segfault when accessing range returned by function
                    that has delegate referencing local variables
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: hsteoh quickfur.ath.cx



import std.algorithm;
import std.range;
import std.stdio;

auto boo() {
    auto C = [2];
    return [1,1].map!((a) => C).joiner;
}

void main() {
    writeln(boo().take(12));
}

This code will either segfault or produce nonsensical output. Replacing (a)=>C
with (a)=>[2] makes the problem go away; shortening [1,1] to [1] also makes the
problem go away, and removing .joiner also makes the problem go away. Removing
the .map makes the problem go away too.

The problem is suspected to be the delegate (a)=>C which references the local
variable C, which goes out of scope when boo() returns. For whatever reason,
dmd isn't emitting code to allocate the delegate's context on the heap, causing
a crash when writeln() tries to read the second element off the range. (I'm not
sure why it doesn't crash with the first element. Maybe luck.)

Replacing the delegate with function(a)=>[1] makes the problem go away.

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Oct 16 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8832




See also issue 7978, probably the same bug in a different context.

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Oct 16 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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I think I may have figured out the cause of this bug. If boo() is modified as
follows:

auto boo() {
    auto C = [2];
    auto d = delegate(int) => C;
    return [1,1].map!d.joiner;
}

then everything works. Seems to me that the compiler is failing to pick up the
reference to C *when the delegate is defined inside the compile-time parameter*
to map. Hopefully this helps narrow it down enough to find the problem in the
dmd code.

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Oct 18 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8832


Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim maxim-fomin.ru



---


 import std.algorithm;
 import std.range;
 import std.stdio;
 
 auto boo() {
     auto C = [2];
     return [1,1].map!((a) => C).joiner;
 }
 
 void main() {
     writeln(boo().take(12));
 }
 
 This code will either segfault or produce nonsensical output. Replacing (a)=>C
 with (a)=>[2] makes the problem go away; shortening [1,1] to [1] also makes the
 problem go away, and removing .joiner also makes the problem go away. Removing
 the .map makes the problem go away too.
 
 The problem is suspected to be the delegate (a)=>C which references the local
 variable C, which goes out of scope when boo() returns. For whatever reason,
 dmd isn't emitting code to allocate the delegate's context on the heap, causing
 a crash when writeln() tries to read the second element off the range. (I'm not
 sure why it doesn't crash with the first element. Maybe luck.)
 
 Replacing the delegate with function(a)=>[1] makes the problem go away.


The problem is in erroneous treating (a) => C of type void. If this is fixed
to:
- delegate(int a) { return C; }
- (int a) { return C; )
- (int a) => C;
everything works fine.

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Oct 26 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8832


Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com



00:41:00 PST ---
A clearer test case:

import std.algorithm;
import std.range;
import std.stdio;

auto boo() {
    auto C = [2];
    auto bar(int) { return C; }
    return [1,1].map!(bar).joiner;
}

void main() {
    writeln(boo().take(12));
}

The problem is that joiner!(MapResult!(bar,int[])) is not recognized as a
'local' template instantiation, even though MapResult!(bar,int[]) is marked as
local. Hence, boo() is not marked as needing a closure (case (4) in
FuncDeclaration::needsClosure()).

The fix listed for Issue 8863 correctly fixes this one. But there are other
problems with that fix, as listed in 8863.

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Dec 29 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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19:34:47 PST ---
Interestingly, Don's fix:

https://github.com/D-Programming-Language/dmd/pull/1554

fixes my clearer test case, but not the original.

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Jan 28 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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21:09:49 PST ---
https://github.com/D-Programming-Language/dmd/pull/1575

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Jan 28 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/63bba9d02ad4ff783c10c543c2c9ea4e91248873
fix Issue 8832 - Segfault when accessing range returned by function that has
delegate referencing local variables

https://github.com/D-Programming-Language/dmd/commit/fe7583317aefdc63e5dc233a627296c5df5594e3


fix Issue 8832 - Segfault when accessing range returned by function that...

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prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


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