RFC: don't disable shlib breakpoints in a.out executables

[Jim Blandy <jimb@cygnus.com>]

The ChangeLog records some vacillation on this question; I think this
is the right solution.  I've tested it on Linux, Solaris, and SunOS 4,
with good results.

Folks have expressed misgivings about testing the BFD flavor at
run-time, instead of having a platform-specific #define.  The comment
in the code explains why the decision needs to be made at run-time.

In the long run, solib.c should be split into separate SysV and SunOS
modules.


1999-06-23  Jim Blandy  <jimb@zwingli.cygnus.com>

	* solib.c (clear_solib): Don't disable breakpoints if we're
	running an a.out executable (Solaris's SunOS emulation).

Index: solib.c
===================================================================
RCS file: /cvs/cvsfiles/devo/gdb/solib.c,v
retrieving revision 1.124
diff -c -c -b -F'^(' -r1.124 solib.c
*** solib.c	1999/04/07 01:19:52	1.124
--- solib.c	1999/06/23 19:06:33
***************
*** 1306,1315 ****
  /* Called by free_all_symtabs */
  
  void 
! clear_solib()
  {
    struct so_list *next;
    char *bfd_filename;
  
    while (so_list_head)
      {
--- 1306,1339 ----
  /* Called by free_all_symtabs */
  
  void 
! clear_solib ()
  {
    struct so_list *next;
    char *bfd_filename;
+ 
+   /* This function is expected to handle ELF shared libraries.  It is
+      also used on Solaris, which can run either ELF or a.out binaries
+      (for compatibility with SunOS 4), both of which can use shared
+      libraries.  So we don't know whether we have an ELF executable or
+      an a.out executable until the user chooses an executable file.
+ 
+      ELF shared libraries don't get mapped into the address space
+      until after the program starts, so we'd better not try to insert
+      breakpoints in them immediately.  We have to wait until the
+      dynamic linker has loaded them; we'll hit a bp_shlib_event
+      breakpoint (look for calls to create_solib_event_breakpoint) when
+      it's ready.
+ 
+      SunOS shared libraries seem to be different --- they're present
+      as soon as the process begins execution, so there's no need to
+      put off inserting breakpoints.  There's also nowhere to put a
+      bp_shlib_event breakpoint, so if we put it off, we'll never get
+      around to it.
+ 
+      So: disable breakpoints only if we're using ELF shared libs.  */
+   if (exec_bfd != NULL
+       && bfd_get_flavour (exec_bfd) != bfd_target_aout_flavour)
+     disable_breakpoints_in_shlibs (1);
  
    while (so_list_head)
      {