[Bug cli/17349] New: gdb doesn't read symbol table file specified by -symbols (or -s) option

["mark.plotnick at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17349

            Bug ID: 17349
           Summary: gdb doesn't read symbol table file specified by
                    -symbols (or -s) option
           Product: gdb
           Version: 7.8
            Status: NEW
          Severity: normal
          Priority: P2
         Component: cli
          Assignee: unassigned at sourceware dot org
          Reporter: mark.plotnick at gmail dot com

gdb (in main.c:captured_main), while processing its command line options, sets
symarg to the argument that follows -s, but then later in the code, it
unconditionally sets symarg to the executable's name. So the symbol table file
the user specified is not read in.

This was originally reported by a user on Stack Overflow.
http://stackoverflow.com/questions/25625155/why-doesnt-the-gdb-s-option-load-the-symbol-file/

Here's how to reproduce the problem (On Ubuntu 14.04, with gdb 7.7):

$ cat ab.c
#include <stdlib.h>

main()
{
    abort();
}

$ cc -g ab.c -o ab
$ objcopy --only-keep-debug ab ab.dbg
$ objcopy --strip-debug ab
$ ./ab
Aborted (core dumped)
$ gdb -s ./ab.dbg ./ab ./core
GNU gdb (Ubuntu 7.7-0ubuntu3.1) 7.7
Reading symbols from ./ab...(no debugging symbols found)...done.
[New LWP 11244]
Core was generated by `./ab'.
Program terminated with signal SIGABRT, Aborted.
#0  0x00007f6488d83bb9 in __GI_raise (sig=sig@entry=6) at
../nptl/sysdeps/unix/sysv/linux/raise.c:56
56    ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007f6488d83bb9 in __GI_raise (sig=sig@entry=6) at
../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007f6488d86fc8 in __GI_abort () at abort.c:89
#2  0x0000000000400536 in main ()
(gdb) symbol-file ./ab.dbg
Load new symbol table from "./ab.dbg"? (y or n) y
Reading symbols from ./ab.dbg...done.
(gdb) bt
#0  0x00007f6488d83bb9 in __GI_raise (sig=sig@entry=6) at
../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007f6488d86fc8 in __GI_abort () at abort.c:89
#2  0x0000000000400536 in main () at ab.c:5

The symbol-file command was required in order to load the symbol table and
provide line number info for main().

My try at a minimal fix:
A couple ways to fix it. You know best.

$ diff -C 1 main.c.orig main.c
*** main.c.orig 2014-07-29 08:37:42.000000000 -0400
--- main.c      2014-09-02 16:27:54.079039046 -0400
***************
*** 864,866 ****
        }
!       symarg = argv[optind];
        execarg = argv[optind];
--- 864,866 ----
        }
!       if (symarg == NULL) symarg = argv[optind];
        execarg = argv[optind];
***************
*** 877,879 ****
        {
!         symarg = argv[optind];
          execarg = argv[optind];
--- 877,879 ----
        {
!         if (symarg == NULL) symarg = argv[optind];
          execarg = argv[optind];

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