Re: Problem compiling gdb/symtab.c in GDB 6.7.1 using GCC 4.3.0 on Solaris 10 (already fixed in GDB 6.8 code)

[Jonathan Leffler]

Dear Bug-GDB Team,

This got entered into GCC's Bugzilla as Bug 35534.  It has been closed, but you can follow events there.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35534

Having downloaded a CVS snapshot of GDB 6.8 code, there is a coded fix for the problem in the (static) function find_line_common(), which indeed had a pair of return statements wherein 'exact' was not assigned a value.  Close human inspection of the code can see that when exact is not set, best_index is negative so exact is not read.  However, it would be pushing the compiler to the limits to spot that.

Since the fix is already coded in the dev snapshot, you don't need to open a bug for this - or you can close the bug created for it if one was already created.  But be aware that people will run into this problem if they compile GDB 6.7.1 with GCC 4.3.0.

Sorry for any trouble I have caused.

On Mon, Mar 10, 2008 at 8:24 PM, Jonathan Leffler <address@hidden> wrote:

I'm not clear whether this is a problem in GCC or in GDB, so I'm asking both teams.

Compiling gdb 6.7.1 on Solaris 10 using the newly installed GCC 4.3.0, I got a compilation error (because of the -Werror option) as shown:

gcc -c -g -O2    -I. -I.././gdb -I.././gdb/config -DLOCALEDIR="\"/usr/gdb/v6.7.1/share/locale\"" -DHAVE_CONFIG_H -I.././gdb/../include/opcode -I.././gdb/../readline/.. -I../bfd -I.././gdb/../bfd -I.././gdb/../include -I./../intl  -DMI_OUT=1 -DTUI=1  -Wall -Wdeclaration-after-statement -Wpointer-arith -Wformat-nonliteral -Wno-pointer-sign -Wno-unused -Wno-switch -Wno-char-subscripts -Werror symtab.c
cc1: warnings being treated as errors
symtab.c: In function 'find_line_symtab':
symtab.c:2252: error: 'exact' may be used uninitialized in this function
make: *** [symtab.o] Error 1

The fragment in question was 'worked around' by adding the '= 0' to the declaration of 'exact' at:

struct symtab *
find_line_symtab (struct symtab *symtab, int line, int *index, int *exact_match)
{
  int exact = 0;

  /* BEST_INDEX and BEST_LINETABLE identify the smallest linenumber > LINE
     so far seen.  */

  int best_index;
  struct linetable *best_linetable;
  struct symtab *best_symtab;

  /* First try looking it up in the given symtab.  */
  best_linetable = LINETABLE (symtab);
  best_symtab = symtab;
  best_index = find_line_common (best_linetable, line, &exact);
  if (best_index < 0 || !exact)
    {

It is not clear to me that GCC is entitled to complain.  However, given that it does, the workaround at least allows the compilation to proceed.

[...]

-- 
Jonathan Leffler <address@hidden> #include <disclaimer.h>
Guardian of DBD::Informix - v2008.0229 - http://dbi.perl.org
"Blessed are we who can laugh at ourselves, for we shall never cease to be amused."