Re: RFA: handle zero-length types in value_from_register

[Jim Blandy <jimb at redhat dot com>]

Andrew Cagney <cagney@gnu.org> writes:
> > Andrew Cagney <cagney@gnu.org> writes:
> >
> >> > 2004-01-27  Jim Blandy  <jimb@redhat.com>
> >> > 	* findvar.c (value_from_register): If the type has no length,
> >> > just
> >> > 	return an acceptable value --- don't report an internal error.
> >> >
> >
> >> This looks to need a test case.
> > I tried to put one together, but the bug only occurs when the
> > zero-length value is allocated to a register.  I couldn't find any way
> > to make that happen at all.  So the only known instance of this bug
> > depends on bad debug info.
> 
> The commentary should really reflect this important detail (also
> mention the compiler that's broken for instance).  Should GDB also
> complain about the bogus info?

Seems reasonable.  I've attached a revision of the original patch,
with an expanded comment, and a separate patch that makes GDB complain
when it sees the bogus info.

2004-01-27  Jim Blandy  <jimb@redhat.com>

	* findvar.c (value_from_register): If the type has no length, just
	return an acceptable value --- don't report an internal error.

Index: gdb/findvar.c
===================================================================
RCS file: /cvs/src/src/gdb/findvar.c,v
retrieving revision 1.68
diff -c -r1.68 findvar.c
*** gdb/findvar.c	26 Jan 2004 20:36:32 -0000	1.68
--- gdb/findvar.c	28 Jan 2004 05:47:05 -0000
***************
*** 617,623 ****
    struct value *v = allocate_value (type);
    CHECK_TYPEDEF (type);
  
!   if (CONVERT_REGISTER_P (regnum, type))
      {
        /* The ISA/ABI need to something weird when obtaining the
           specified value from this register.  It might need to
--- 617,646 ----
    struct value *v = allocate_value (type);
    CHECK_TYPEDEF (type);
  
!   if (TYPE_LENGTH (type) == 0)
!     {
!       /* It doesn't matter much what we return for this: since the
!          length is zero, it could be anything.  But if allowed to see
!          a zero-length type, the register-finding loop below will set
!          neither mem_stor nor reg_stor, and then report an internal
!          error.  
! 
!          Zero-length types can legitimately arise from declarations
!          like 'struct {}'.  GDB may also create them when it finds
!          bogus debugging information; for example, in GCC 2.94.4 and
!          binutils 2.11.93.0.2, the STABS BINCL->EXCL compression
!          process can create bad type numbers.  GDB reads these as
!          TYPE_CODE_UNDEF types, with zero length.  (That bug is
!          actually the only known way to get a zero-length value
!          allocated to a register --- which is what it takes to make it
!          here.)
! 
!          We'll just attribute the value to the original register.  */
!       VALUE_LVAL (v) = lval_register;
!       VALUE_ADDRESS (v) = regnum;
!       VALUE_REGNO (v) = regnum;
!     }
!   else if (CONVERT_REGISTER_P (regnum, type))
      {
        /* The ISA/ABI need to something weird when obtaining the
           specified value from this register.  It might need to

2004-01-27  Jim Blandy  <jimb@redhat.com>

	* stabsread.c (read_type): If we find any type numbers that are
	forward references, complain if the references aren't resolved by
	the time we're finished reading.
	(cleanup_undefined_types): Make error message more appropriate for
	a complaint.

Index: gdb/stabsread.c
===================================================================
RCS file: /cvs/src/src/gdb/stabsread.c,v
retrieving revision 1.72
diff -c -r1.72 stabsread.c
*** gdb/stabsread.c	19 Jan 2004 01:20:11 -0000	1.72
--- gdb/stabsread.c	28 Jan 2004 05:39:16 -0000
***************
*** 1446,1456 ****
        if (read_type_number (pp, typenums) != 0)
  	return error_type (pp, objfile);
  
-       /* Type is not being defined here.  Either it already exists,
-          or this is a forward reference to it.  dbx_alloc_type handles
-          both cases.  */
        if (**pp != '=')
! 	return dbx_alloc_type (typenums, objfile);
  
        /* Type is being defined here.  */
        /* Skip the '='.
--- 1446,1466 ----
        if (read_type_number (pp, typenums) != 0)
  	return error_type (pp, objfile);
  
        if (**pp != '=')
!         {
!           /* Type is not being defined here.  Either it already
!              exists, or this is a forward reference to it.
!              dbx_alloc_type handles both cases.  */
!           type = dbx_alloc_type (typenums, objfile);
! 
!           /* If this is a forward reference, arrange to complain if it
!              doesn't get patched up by the time we're done
!              reading.  */
!           if (TYPE_CODE (type) == TYPE_CODE_UNDEF)
!             add_undefined_type (type);
! 
!           return type;
!         }
  
        /* Type is being defined here.  */
        /* Skip the '='.
***************
*** 4197,4203 ****
  	default:
  	  {
  	    complaint (&symfile_complaints,
! 		       "GDB internal error.  cleanup_undefined_types with bad type %d.",
  		       TYPE_CODE (*type));
  	  }
  	  break;
--- 4207,4214 ----
  	default:
  	  {
  	    complaint (&symfile_complaints,
! 		       "forward-referenced types left unresolved, "
!                        "type code %d.",
  		       TYPE_CODE (*type));
  	  }
  	  break;