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digitalmars.D.bugs - [Issue 9028] New: `main` is trated sometimes as having C linkage and sometimes as having D linkage

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9028

           Summary: `main` is trated sometimes as having C linkage and
                    sometimes as having D linkage
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: verylonglogin.reg gmail.com


--- Comment #0 from Denis Shelomovskij <verylonglogin.reg gmail.com> 2012-11-15
11:59:34 MSK ---
---
void main(string[] args)
{
    if(!args.length) return;

    foreach(i; 0 .. 1)
        main(null); // ok, C linkage used

    foreach(i; 0 .. 1)
        (&main)(null); // also ok

    foreach(i; 0 .. 1)
    {
        auto p = &main; // D linkage used
        p(null); // stack corruption, results in Access Violation
      //asm { add ESP, 0x8; } // uncomment to fix
    }
}
---

Note: do not mark `main` as `extern(C)` because it will lead to not calling
runtime initialization stuff.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9028


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

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


--- Comment #1 from Maxim Fomin <maxim maxim-fomin.ru> 2012-11-15 01:49:06 PST
---
I don't understand what is the problem here. First of all the code runs on both
win&lin using dmd 2.060 and git head from Dpaste. Secondly I don't understand
how this is related to linkage. Function calls main(null) and (&main)(null) are
equivalent. In the third case you call it indirectly through pointer.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Denis Shelomovskij <verylonglogin.reg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|`main` is trated sometimes  |`main` is trated sometimes
                   |as having C linkage and     |as having C calling
                   |sometimes as having D       |convention and sometimes as
                   |linkage                     |having D convention


--- Comment #2 from Denis Shelomovskij <verylonglogin.reg gmail.com> 2012-11-15
13:01:22 MSK ---
(In reply to comment #1)

Sorry, it's calling convention, not linkage.

I mean C calling convention is used in first two cases but as `typeof(main)`
tells it is `extern(D)` D calling convention is used in the last case.

So `Access Violation` isn't mandatory but possible.

I.e. this will print decreasing ESP:
---
import std.stdio;

void main(string[] args)
{
    if(!args.length) return;

    size_t esp;
    foreach(i; 0 .. 2 ^^ 20)
    {
        auto p = &main; // D linkage used
        p(null); // stack corruption, results in Access Violation
      //asm { add ESP, 0x8; } // uncomment to fix
        asm { mov esp, ESP; }
        writefln("%X", esp);
    }
}
---

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--- Comment #3 from Maxim Fomin <maxim maxim-fomin.ru> 2012-11-15 03:11:18 PST
---
Ok, I see the problem now:
-------------------------
import std.stdio;

void main(string[] args)
{
    dain(args);
    if(!args.length) return;

    foreach(i; 0 .. 2)
    {
        size_t esp;
        main(null); // ok, C linkage used
        asm { mov esp, ESP; }
        writeln("main");
        writefln("%X", esp);
    }

    foreach(i; 0 .. 2)
    {
        size_t esp;
        (&main)(null); // also ok
        asm { mov esp, ESP; }
        writeln("&main");
        writefln("%X", esp);
    }


    foreach(i; 0 .. 2)
    {
        size_t esp;
        auto p = &main; // D linkage used
        p(null); // stack corruption, results in Access Violation
        //asm { add ESP, 0x8; } // uncomment to fix
        asm { mov esp, ESP; }
        writeln("p-main");
        writefln("%X", esp);
    }
}

void dain(string[] args)
{
    if(!args.length) return;

    foreach(i; 0 .. 2)
    {
        size_t esp;
        dain(null); // ok, C linkage used
        asm { mov esp, ESP; }
        writeln("dain");
        writefln("%X", esp);
    }

    foreach(i; 0 .. 2)
    {
        size_t esp;
        (&dain)(null); // also ok
        asm { mov esp, ESP; }
        writeln("&dain");
        writefln("%X", esp);
    }


    foreach(i; 0 .. 2)
    {
        size_t esp;
        auto p = &dain; // D linkage used
        p(null); // stack corruption, results in Access Violation
        //asm { add ESP, 0x8; } // uncomment to fix
        asm { mov esp, ESP; }
        writeln("p-dain");
        writefln("%X", esp);
    }
}
----------------------------------
dain
18FDC4
dain
18FDC4
&dain
18FDC4
&dain
18FDC4
p-dain
18FDC4
p-dain
18FDC4
main
18FE10
main
18FE10
&main
18FE10
&main
18FE10
p-main
18FE08
p-main
18FE00

This is windows output. Note in main %esp is decreasing in last loop. 

Same code on linux is fine (http://dpaste.dzfl.pl/6aa48fed), so this is
specific to windows codegen/calling conventions.

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prev sibling parent d-bugmail puremagic.com writes:
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--- Comment #4 from github-bugzilla puremagic.com 2012-11-15 06:59:22 PST ---
Commit pushed to master at https://github.com/D-Programming-Language/druntime

https://github.com/D-Programming-Language/druntime/commit/d171d502d6cb1420140053267cb51989b0f2d07e
Add full workaround for Issue 9028.

Mark D main as `extern(C)` and use its symbol name to workaround Issue 9028.
Also add comments about `D main` type and actual calling convention.

* Issue 9028 URL: http://d.puremagic.com/issues/show_bug.cgi?id=9028

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