[Bug debug/49032] New: -gstabs generates reference to deleted static variable

[Bug debug/49032] New: -gstabs generates reference to deleted static variable

[arthur.j.odwyer at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49032

           Summary: -gstabs generates reference to deleted static variable
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: arthur.j.odwyer@gmail.com


Created attachment 24272
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24272
Output of "ajo-gcc -w -O1 -gstabs test.c -o a.out -v"

This reproduces for me with svn revision 173589 (2011-05-09). It doesn't
reproduce with gcc 4.5.1. I'm on Ubuntu 10.10, x86-64.

cat >test.c <<EOF
static struct S2 {
  int x;
} g_239[8] = {42};

int main() {
    struct S2 *l_845[2][9] = {{0,0,0,0,0,0,0,0,0},
        {0,0,0,0, &g_239[6], &g_239[6], &g_239[6], &g_239[6], &g_239[6]}};
    return 0;
}
EOF
gcc -w -O1 -gstabs test.c -o a.out

/tmp/ccknU0Y6.o: In function `main':
test.c:9: undefined reference to `g_239'
collect2: ld returned 1 exit status

This linker error is due to the following lines in the generated test.s:

.Lscope1:
        .stabs  "g_239:S(0,22)=ar(0,23)=r(0,23);0;-1;;0;7;(0,21)",38,0,0,g_239

Someone sees that g_239 is an unused file-static variable and therefore deletes
it --- correctly, IMHO --- but incorrectly forgets to also remove the debug
information's references to g_239.


This test case is reduced from the output of Csmith 2.1.0 (git hash 541a6480,
https://github.com/csmith-project/csmith/), using the following command line:
csmith --no-paranoid --no-longlong --pointers --arrays --jumps --consts
--no-volatiles --no-checksum --divs --no-muls --bitfields --no-packed-struct -s
891890068

[Bug debug/49032] -gstabs generates reference to deleted static variable

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49032

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-19 17:07:35 UTC ---
Created attachment 24293
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24293
gcc47-pr49032.patch

Untested fix.  Works on this testcase, as well as when s is actually forced to
be output (e.g. through inline asm).  I'm not a stabs user (are there any left
anyway?), so don't know whether it doesn't decrease debug info quality (if we
can speak about debug info quality in stabs case), but from I understand at
least the global_decl debug hooks are called at least by C/C++ FEs after
cgraph_finalize_compilation_unit has been called and thus IMHO the patch should
only change anything when the vars aren't output.
Guess one could put there instead gcc_unreachable (); instead of return NULL;
and see how often it triggers during -gstabs bootstrap.

[Bug debug/49032] -gstabs generates reference to deleted static variable

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49032

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-23 18:07:46 UTC ---
Author: jakub
Date: Mon May 23 18:07:43 2011
New Revision: 174083

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174083
Log:
    PR debug/49032
    * dbxout.c: Include cgraph.h.
    (dbxout_expand_expr): If a VAR_DECL is TREE_STATIC, not written
    and without value expr, return NULL if no varpool node exists for
    it or if it is not needed.
    * Makefile.in (dbxout.o): Depend on $(CGRAPH_H).

    * gcc.dg/debug/pr49032.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/debug/pr49032.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/Makefile.in
    trunk/gcc/dbxout.c
    trunk/gcc/testsuite/ChangeLog

[Bug debug/49032] -gstabs generates reference to deleted static variable

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49032

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |jakub at gcc dot gnu.org
         Resolution|                            |FIXED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-23 18:19:18 UTC ---
Fixed.

[Bug debug/49032] -gstabs generates reference to deleted static variable

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49032

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-23 18:12:36 UTC ---
Author: jakub
Date: Mon May 23 18:12:34 2011
New Revision: 174084

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174084
Log:
    PR debug/49032
    * dbxout.c: Include cgraph.h.
    (dbxout_expand_expr): If a VAR_DECL is TREE_STATIC, not written
    and without value expr, return NULL if no varpool node exists for
    it or if it is not needed.
    * Makefile.in (dbxout.o): Depend on $(CGRAPH_H).

    * gcc.dg/debug/pr49032.c: New test.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/gcc.dg/debug/pr49032.c
Modified:
    branches/gcc-4_6-branch/gcc/ChangeLog
    branches/gcc-4_6-branch/gcc/Makefile.in
    branches/gcc-4_6-branch/gcc/dbxout.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog