[Bug c/24097] New: x86_64 -fPIC code gen bug (extern/static linkage confusion)

[Bug c/24097] New: x86_64 -fPIC code gen bug (extern/static linkage confusion)

[mcoiley at yahoo dot com]

With this testcase:

int foo (int (*cb)(void)) { return (*cb)(); }
static int callback(void) { return 0; }

int main (void)
{
 int callback (void);
 return foo (callback);
}

On x86_64 with -fPIC, the address of callback as passed to foo is incorrect.

If callback isn't static, it works (through the GOT).  If the declaration of
callback is removed it works (computes the address as %rip minus something).  As
written, it does a failed combination of the two.  The result is that instead of
passing callback's address, it loads the first 8 bytes at callback's address and
passes those.  (It also erroneously claims callback is unused, but I'm guessing
that's a side-effect.)

The code is questionable, but my reading of the standard says it's legal and
that callback is still static after the (implicitly extern) declaration.

% gcc-3.4.4 -O2 -fPIC -Wall -save-temps -o bug bug.c 
bug.c:2: warning: 'callback' defined but not used

% gcc-3.4.4 -v
Reading specs from /usr/local/lib/gcc/x86_64-pc-linux-gnu/3.4.4/specs
Configured with: /tmp/src/gcc-3.4.4/configure --enable-languages=c,c++
--enable-version-specific-runtime-libs --disable-shared --enable-threads
--with-gnu-as --with-gnu-ld --with-pic --host=x86_64-pc-linux-gnu
Thread model: posix
gcc version 3.4.4

[I bootstrapped this 3.4.4; it also fails with stock 3.4.3 from RedHat.]

-- 
           Summary: x86_64 -fPIC code gen bug (extern/static linkage
                    confusion)
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mcoiley at yahoo dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: x86_64-pc-linux-gnu
  GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097

[Bug c/24097] [3.4 Regression] x86_64 -fPIC code gen bug (extern/static linkage confusion)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-28 02:48 -------
Confirmed, only a 3.4 regression.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
  GCC build triplet|x86_64-pc-linux-gnu         |
   GCC host triplet|x86_64-pc-linux-gnu         |
           Keywords|                            |wrong-code
      Known to fail|                            |3.4.0 3.4.5
      Known to work|                            |3.3.3 4.0.0 4.1.0
   Last reconfirmed|0000-00-00 00:00:00         |2005-09-28 02:48:38
               date|                            |
            Summary|x86_64 -fPIC code gen bug   |[3.4 Regression] x86_64 -
                   |(extern/static linkage      |fPIC code gen bug
                   |confusion)                  |(extern/static linkage
                   |                            |confusion)
   Target Milestone|---                         |3.4.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097

[Bug c/24097] [3.4 Regression] x86_64 -fPIC code gen bug (extern/static linkage confusion)

[mcoiley at yahoo dot com]

------- Additional Comments From mcoiley at yahoo dot com  2005-09-28 18:49 -------
*** Bug 24106 has been marked as a duplicate of this bug. ***

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097

[Bug c/24097] [3.4 Regression] x86_64 -fPIC code gen bug (extern/static linkage confusion)

[gdr at gcc dot gnu dot org]

------- Comment #5 from gdr at gcc dot gnu dot org  2006-03-01 04:50 -------
Fixed in 4.0.0 and up.


-- 

gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|3.4.6                       |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097

[Bug c/24097] [3.4 Regression] x86_64 -fPIC code gen bug (extern/static linkage confusion)

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2006-02-14 00:19 -------
IIRC this was fixed by a latter rewrite of c-decl.c and most likely not going
to be fixed for 3.4.x.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097

[Bug c/24097] [3.4 Regression] x86_64 -fPIC code gen bug (extern/static linkage confusion)

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2006-02-14 00:17 -------
*** Bug 26271 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |josh dot parsons at stonebow
                   |                            |dot otago dot ac dot nz


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097

[Bug c/24097] [3.4 Regression] x86_64 -fPIC code gen bug (extern/static linkage confusion)

[gdr at gcc dot gnu dot org]

-- 

gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.5                       |3.4.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24097