[RFA/RFC] Fix broken user-thread debugging on x86-solaris

[Joel Brobecker <brobecker at adacore dot com>]

Hello,

While testing GDB on x86-solaris, I noticed that the debugger now prints
a warning during startup:

    % ./gdb
    [GDB will not be able to debug user-mode threads: ld.so.1: gdb.ref: fatal: relocation error: file /usr/lib/libthread_db.so.1: symbol ps_lgetLDT: referenced symbol not found]
    GNU gdb 6.8.50.20080311-cvs
    Copyright (C) 2008 Free Software Foundation, Inc.
    [...]

The problem was introduced when we killed the TM file, which was
defining the TM_I386SOL2_H macro that a couple of units were actually
using (ugh!).

Basically, the problem on x86-solaris is that, in order to load
libthread_db.so, we need to define ps_lgetLDT or the loading
will fail due to this symbol being undefined.  This function is
defined inside sol-thread.c but is conditionalized on TM_I386SOL2_H
being defined:

    #ifdef TM_I386SOL2_H
    
    /* Reads the local descriptor table of a LWP.  */
    
    ps_err_e
    ps_lgetLDT (gdb_ps_prochandle_t ph, lwpid_t lwpid,
                struct ssd *pldt)
    {

Similarly, a couple of other functions inside procfs.c that
this function uses are conditionalized on the same macro:
proc_get_LDT_entry and procfs_find_LDT_entry. This stuff is
entirely x86-solaris specific, so cannot be enabled on sparc-solaris.

I think the most classical way of fixing this would be to move these
to their own file, such as sol-x86-thread.c. But I'm not sure whether
this is going to be the prefered solution in this case, because
the procfs routines need access to certain fields of a structure
that is not public (struct procinfo).

In this version, I went to the simplest, which is to have configure
define a new macro (HAVE_X86_SOLARIS_USER_THREADS) when on x86-solaris
and the thread_db library is available.  I then replaced TM_I386SOL2_H
by the new macro.

If I were to move the 3 functions to their own file, I would have
to create procfs.h to provide an opaque definition of struct procinfo.
I would also add a few accessor routines (to get the pid and the ctl_fd),
and make a few routines such as find_procinfo or proc_get_gregs non-static.
I don't mind doing this work, but I want to make sure others prefer it too.

2008-03-12  Joel Brobecker  <brobecker@adacore.com>

        * configure.ac (HAVE_X86_SOLARIS_USER_THREADS): Define this macro
        if we are building a native x86-solaris debugger that has access
        to user-threads.
        * configure, config.in: Regenerate.
        * sol-thread.c, procfs.c : Use HAVE_X86_SOLARIS_USER_THREADS
        in place of TM_I386SOL2_H.

Tested on x86-solaris. No regression.
Opinions?

BTW: We should fix this in the branch as well.

Thanks,
-- 
Joel

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