[Bug c++/31775] New: static object mangling conflicts with extern object

[Bug c++/31775] New: static object mangling conflicts with extern object

[geoffk at gcc dot gnu dot org]

In [basic.link] paragraph 6, there's an example that shows that (unlike in C)
it is permissible to define an object 'static' in a namespace scope and then
have another object which is 'extern', and reference both in the same
translation unit.

The compiler optimises that example so that there's no way to see the incorrect
behaviour, but a slightly modified version is:

extern "C" void abort();
static int i;
int *p = &i;
int main()
{ 
  int i;
  { 
    extern int i;
    i = 1;
    *p = 2;
    if (i == 2)
      abort ();
  }
  return 0;
}

I believe this should fail to compile with a link error, because the extern
version of 'i' is never defined.  On Darwin, what this does (apparently) is
crash with a bus error trying to write to the first instruction of main, which
is probably a linker bug; I expect that on other OSs it will call abort().

The basic problem is that 'static int i' needs to be a different name in the
assembly than 'extern int i'.


-- 
           Summary: static object mangling conflicts with extern object
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: geoffk at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[geoffk at gcc dot gnu dot org]

------- Comment #1 from geoffk at gcc dot gnu dot org  2007-05-01 19:56 -------
This testcase is the same principle, but might use a different code path in the
compiler:

extern "C" void abort();
extern int *p;
int main()
{ 
  extern int i;
  i = 1;
  *p = 2;
  if (i == 2)
    abort ();
  return 0;
}

static int i;
int *p = &i;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2007-05-01 20:44 -------
How do you define main"::"i?  That is, how'd you make the testcase work from a
second translation unit if it would fail now?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[geoffk at gcc dot gnu dot org]

------- Comment #3 from geoffk at gcc dot gnu dot org  2007-05-02 00:54 -------
You would add a translation unit that says

int i;

or similar.  It's not "main::i", it's "::i", because of [basic.link] paragraph
7:

When a block scope declaration of an entity with linkage is not found to refer
to some other declaration, 
then that entity is a member of the innermost enclosing namespace.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[geoffk at gcc dot gnu dot org]

------- Comment #4 from geoffk at gcc dot gnu dot org  2007-05-02 01:46 -------
I just happen to have a patch which fixes this.


-- 

geoffk at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |geoffk at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-05-02 01:46:13
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[geoffk at gcc dot gnu dot org]

------- Comment #5 from geoffk at gcc dot gnu dot org  2007-05-06 01:01 -------
Subject: Bug 31775

Author: geoffk
Date: Sun May  6 00:01:36 2007
New Revision: 124467

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124467
Log:
Index: libiberty/ChangeLog
2007-05-04  Geoffrey Keating  <geoffk@apple.com>

        * cp-demangle.c (d_name): Detect local-source-name.
        (d_prefix): Likewise.
        (d_unqualified_name): Implement local-source-name.

Index: gcc/cp/ChangeLog
2007-05-04  Geoffrey Keating  <geoffk@apple.com>

        PR 31775
        * mangle.c (write_mangled_name): Mangle static variable names.
        (write_unqualified_name): Use local-source-name for
        namespace-scope static variables.

Index: gcc/testsuite/ChangeLog
2007-05-04  Geoffrey Keating  <geoffk@apple.com>

        PR 31775
        * g++.dg/other/nested-extern.cc: New.
        * g++.dg/other/nested-extern-1.C: New.
        * g++.dg/other/nested-extern-2.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/other/nested-extern-1.C
    trunk/gcc/testsuite/g++.dg/other/nested-extern-2.C
    trunk/gcc/testsuite/g++.dg/other/nested-extern.cc
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/mangle.c
    trunk/gcc/testsuite/ChangeLog
    trunk/libiberty/ChangeLog
    trunk/libiberty/cp-demangle.c
    trunk/libiberty/testsuite/demangle-expected


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[geoffk at gcc dot gnu dot org]

------- Comment #6 from geoffk at gcc dot gnu dot org  2007-05-06 01:27 -------
That should do it.


-- 

geoffk at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[mueller at gcc dot gnu dot org]

------- Comment #7 from mueller at gcc dot gnu dot org  2008-02-29 13:57 -------
how about 

extern "C" void abort();
extern "C" { static int i; }
int *p = &i;
int main()
{ 
  int i;
  { 
    extern int i;
    i = 1;
    *p = 2;
    if (i == 2)
      abort ();
  }
  return 0;
}

in this case, the "i" name should not be mangled, right?


-- 

mueller at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mueller at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[geoffk at geoffk dot org]

------- Comment #8 from geoffk at geoffk dot org  2008-03-01 04:05 -------
Subject: Re:  static object mangling conflicts with extern object


On 29/02/2008, at 5:57 AM, mueller at gcc dot gnu dot org wrote:

> extern "C" void abort();
> extern "C" { static int i; }
> int *p = &i;
> int main()
> {
>  int i;
>  {
>    extern int i;
>    i = 1;
>    *p = 2;
>    if (i == 2)
>      abort ();
>  }
>  return 0;
> }
>
> in this case, the "i" name should not be mangled, right?

It should be mangled, because there are still three different things  
named 'i' declared in this program, and so the two that have assembler  
names have to have different names, and I don't think we want to start  
mangling non-static variable names.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

Re: [Bug c++/31775] static object mangling conflicts with extern object

[Andrew Pinski]

Sent from my iPhone

On Feb 29, 2008, at 20:05, "geoffk at geoffk dot org" <gcc-bugzilla@gcc.gnu.org 
 > wrote:

>
>
> ------- Comment #8 from geoffk at geoffk dot org  2008-03-01 04:05  
> ----
>>
>
> It should be mangled, because there are still three different things
> named 'i' declared in this program, and so the two that have assembler
> names have to have different names, and I don't think we want to start
> mangling non-static variable names.

Also mangling non-static variables will cause an ABI change.

Thanks,
Andrew Pinski

[Bug c++/31775] static object mangling conflicts with extern object

[pinskia at gmail dot com]

------- Comment #9 from pinskia at gmail dot com  2008-03-01 04:19 -------
Subject: Re:  static object mangling conflicts with extern object

Sent from my iPhone

On Feb 29, 2008, at 20:05, "geoffk at geoffk dot org" <gcc-bugzilla@gcc.gnu.org 
 > wrote:

>
>
> ------- Comment #8 from geoffk at geoffk dot org  2008-03-01 04:05  
> ----
>>
>
> It should be mangled, because there are still three different things
> named 'i' declared in this program, and so the two that have assembler
> names have to have different names, and I don't think we want to start
> mangling non-static variable names.

Also mangling non-static variables will cause an ABI change.

Thanks,
Andrew Pinski


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775

[Bug c++/31775] static object mangling conflicts with extern object

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775