[Bug target/29943] New: gcc generate incorrect alias symbols for PPC

[Bug target/29943] New: gcc generate incorrect alias symbols for PPC

[raj dot khem at gmail dot com]

The following example(reduced from glibc) compiles differently for ppc target
when using gcc 4.2 as compared to gcc 4.1
It generates the alias symbol as a real symbol instead of creating it as alias.
I get this correct using gcc 4.2 for arm so the problem seems to be affecting
only ppc. This also works ok with gcc 4.1

to reproduce compile the example with -O2

testcase.c
========================================================
extern char **_dl_argv

     __attribute__ ((section (".data.rel.ro")))

     ;

extern char **_dl_argv_internal __attribute__ ((visibility ("hidden")))

     __attribute__ ((section (".data.rel.ro")))

     ;
char **_dl_argv __attribute__ ((section (".data.rel.ro"))) = ((void *)0);
extern __typeof (_dl_argv) _dl_argv_internal __attribute__ ((alias
("_dl_argv")));
char* foo (){
   return _dl_argv_internal[0];
}

=====================================

glibc segfaults in ld.so currently when compiled with gcc 4.2 for ppc due to
this issue.


-- 
           Summary: gcc generate incorrect alias symbols for PPC
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: raj dot khem at gmail dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: powerpc-*-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

------- Comment #1 from amodra at bigpond dot net dot au  2006-11-22 22:21 -------
relevant -O2 assembly is
        .globl _dl_argv
        .globl _dl_argv_internal
        .hidden _dl_argv_internal
        .set    _dl_argv_internal,_dl_argv
        .section        .data.rel.ro,"aw",@progbits
        .align 2
        .set    .LANCHOR0,. + 0
        .type   _dl_argv_internal, @object
        .size   _dl_argv_internal, 4
_dl_argv_internal:
        .zero   4
        .type   _dl_argv, @object
        .size   _dl_argv, 4
_dl_argv:
        .zero   4

-fno-section-anchors generates good code


-- 

amodra at bigpond dot net dot au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2006-11-22 22:21:39
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

------- Comment #2 from amodra at bigpond dot net dot au  2006-11-22 22:27 -------
Removing __attribute__ ((section (".data.rel.ro"))) from _dl_argv_internal also
generates good code.


-- 

amodra at bigpond dot net dot au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |target


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2006-11-22 22:30 -------
.data.rel.ro, isn't that a special section?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

------- Comment #4 from amodra at bigpond dot net dot au  2006-11-22 22:41 -------
Not particularly.  s/.data.rel.ro/.mysect/ does the same thing.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

-- 

amodra at bigpond dot net dot au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |amodra at bigpond dot net
                   |dot org                     |dot au
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-11-22 22:21:39         |2006-11-23 02:12:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[dje at gcc dot gnu dot org]

------- Comment #5 from dje at gcc dot gnu dot org  2006-11-23 02:31 -------
If GCC is not creating the alias correctly, that is a bug.  However, we
previously agreed in PR 28598 that changing sections behind GCC's back is not
guaranteed to work.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[richard at codesourcery dot com]

------- Comment #6 from richard at codesourcery dot com  2006-11-23 05:04 -------
Subject: Re:  [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

"amodra at bigpond dot net dot au" <gcc-bugzilla@gcc.gnu.org> writes:
>          AssignedTo|unassigned at gcc dot gnu   |amodra at bigpond dot net
>                    |dot org                     |dot au

Thanks for taking this Alan.  I'm happy to look at it if you like though.
If it's section-anchor related, then it's my bug.

Richard


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

------- Comment #7 from amodra at bigpond dot net dot au  2006-11-23 08:01 -------
This is the simple patch I've bootstrapped and am currently regression testing.

Index: varasm.c
===================================================================
--- varasm.c    (revision 119100)
+++ varasm.c    (working copy)
@@ -981,6 +981,10 @@ use_blocks_for_decl_p (tree decl)
   if (DECL_INITIAL (decl) == decl)
     return false;

+  /* If this decl is an alias, then we don't want to emit a definition.  */
+  if (lookup_attribute ("alias", DECL_ATTRIBUTES (decl)))
+    return false;
+
   return true;
 }

Another possibility is to check for named sections in handle_alias_attribute
(and alias attributes in handle_section_attribute), possibly giving a
diagnostic.  It's clear that code like

extern int a __attribute__ ((section (".sec1")));
extern int b __attribute__ ((section (".sec2")))
  __attribute__ ((alias ("a")));

is invalid;  b can't alias a and be in a different section.  However, from the
previous discussion over 28598 I gather we don't want to go down the path of
checking section attributes.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[patchapp at dberlin dot org]

------- Comment #8 from patchapp at dberlin dot org  2006-11-23 12:45 -------
Subject: Bug number PR29943

A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is
http://gcc.gnu.org/ml/gcc-patches/2006-11/msg01613.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug target/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

-- 

amodra at bigpond dot net dot au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|amodra at bigpond dot net   |unassigned at gcc dot gnu
                   |dot au                      |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[schwab at suse dot de]

------- Comment #9 from schwab at suse dot de  2007-01-15 13:38 -------
Any news on this one?  AFAICS Richard Sandiford was ok with the patch.


-- 

schwab at suse dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schwab at suse dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[arekm at pld-linux dot org]

------- Comment #10 from arekm at pld-linux dot org  2007-02-14 20:25 -------
*** Bug 30796 has been marked as a duplicate of this bug. ***


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arekm at pld-linux dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arekm at pld-linux dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[mmitchel at gcc dot gnu dot org]

------- Comment #11 from mmitchel at gcc dot gnu dot org  2007-02-19 20:45 -------
Alan --

This patch is OK.  Would you please apply to 4.2 and mainline?

Thanks,

-- Mark


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at gcc dot gnu dot org]

------- Comment #12 from amodra at gcc dot gnu dot org  2007-02-20 01:25 -------
Subject: Bug 29943

Author: amodra
Date: Tue Feb 20 01:25:41 2007
New Revision: 122148

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=122148
Log:
        PR target/29943
        * varasm.c (use_blocks_for_decl_p): Return false for decls with
        alias attribute.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/varasm.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at gcc dot gnu dot org]

------- Comment #13 from amodra at gcc dot gnu dot org  2007-02-20 01:28 -------
Subject: Bug 29943

Author: amodra
Date: Tue Feb 20 01:28:01 2007
New Revision: 122149

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=122149
Log:
        PR target/29943
        * varasm.c (use_blocks_for_decl_p): Return false for decls with
        alias attribute.


Modified:
    branches/gcc-4_2-branch/gcc/ChangeLog
    branches/gcc-4_2-branch/gcc/varasm.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

-- 

amodra at bigpond dot net dot au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |amodra at bigpond dot net
                   |dot org                     |dot au
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-11-23 02:12:55         |2007-02-20 01:28:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943

[Bug middle-end/29943] [4.2/4.3 Regression] gcc generate incorrect alias symbols for PPC

[amodra at bigpond dot net dot au]

------- Comment #14 from amodra at bigpond dot net dot au  2007-02-20 01:29 -------
Patch applied


-- 

amodra at bigpond dot net dot au changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29943