Gdb generates DW_OP_fbreg in location list without DW_AT_frame_base

H. J. Lu hjl@lucon.org
Thu Dec 30 20:52:00 GMT 2004


On Thu, Dec 30, 2004 at 03:28:28PM -0500, Daniel Jacobowitz wrote:
> On Thu, Dec 30, 2004 at 12:23:46PM -0800, H. J. Lu wrote:
> > On Thu, Dec 30, 2004 at 03:07:20PM -0500, Daniel Jacobowitz wrote:
> > > On Thu, Dec 30, 2004 at 11:56:42AM -0800, H. J. Lu wrote:
> > > > DW_AT_frame_base may be needed for location lists of local variables.
> > > > But in case of tls_symbolic_operand, there is no local variable.
> > > > Location lists are used for function parameters.
> > > 
> > > Then why is GDB calling get_frame_base?  It is only called for
> > > DW_OP_fbreg.  If we don't have a frame base, we don't know what
> > > DW_OP_fbreg refers to.
> > 
> > Gcc generates:
> > 
> >  <1><28c955>: Abbrev Number: 47 (DW_TAG_subprogram)
> >      DW_AT_sibling     : <28c98f>
> >      DW_AT_external    : 1
> >      DW_AT_name        : (indirect string, offset: 0x3875d):
> > tls_symbolic_operand
> >      DW_AT_decl_file   : 1
> >      DW_AT_decl_line   : 471
> >      DW_AT_prototyped  : 1
> >      DW_AT_type        : <2887cb>
> >      DW_AT_low_pc      : 0x826c1d0
> >      DW_AT_high_pc     : 0x826c1fc
> >  <2><28c96f>: Abbrev Number: 48 (DW_TAG_formal_parameter)
> >      DW_AT_name        : op
> >      DW_AT_decl_file   : 1
> >      DW_AT_decl_line   : 470
> >      DW_AT_type        : <288a7b>
> >      DW_AT_location    : 120fbf (location list)
> >  <2><28c97e>: Abbrev Number: 49 (DW_TAG_formal_parameter)
> >      DW_AT_name        : (indirect string, offset: 0x3db66): mode
> >      DW_AT_decl_file   : 1
> >      DW_AT_decl_line   : 470
> >      DW_AT_type        : <288e5d>
> >      DW_AT_location    : 121018 (location list)
> > 
> > for
> > 
> > int
> > tls_symbolic_operand (rtx op, enum machine_mode mode ATTRIBUTE_UNUSED)
> > {
> >   return ((GET_CODE (op) == SYMBOL_REF) && (SYMBOL_REF_TLS_MODEL (op)
> > != 0)) && (mode == VOIDmode || GET_MODE (op) == mode);
> > }
> > 
> > It may be a gcc bug after all.
> 
> And what's in the location lists?  If it's DW_OP_fbreg, then I presume
> it's a GCC bug.  According to my reading of the DWARF spec, anyway.
> 

 <1><418c>: Abbrev Number: 47 (DW_TAG_subprogram)
     DW_AT_sibling     : <41c6>	
     DW_AT_external    : 1	
     DW_AT_name        : (indirect string, offset: 0x3133): tls_symbolic_operand	
     DW_AT_decl_file   : 1	
     DW_AT_decl_line   : 471	
     DW_AT_prototyped  : 1	
     DW_AT_type        : <2c>	
     DW_AT_low_pc      : 0x2f0	
     DW_AT_high_pc     : 0x31c	
 <2><41a6>: Abbrev Number: 48 (DW_TAG_formal_parameter)
     DW_AT_name        : op	
     DW_AT_decl_file   : 1	
     DW_AT_decl_line   : 470	
     DW_AT_type        : <2dc>	
     DW_AT_location    : 549	(location list)
 <2><41b5>: Abbrev Number: 49 (DW_TAG_formal_parameter)
     DW_AT_name        : (indirect string, offset: 0x44e5): mode	
     DW_AT_decl_file   : 1	
     DW_AT_decl_line   : 470	
     DW_AT_type        : <6be>	
     DW_AT_location    : 5a2	(location list)

    00000549 000002f0 000002fe (DW_OP_fbreg: 4)
    00000549 000002fe 00000300 (DW_OP_reg0)
    00000549 00000300 00000301 (DW_OP_fbreg: 4)
    00000549 00000301 0000030b (DW_OP_reg0)
    00000549 0000030b 00000311 (DW_OP_fbreg: 4)
    00000549 00000311 00000315 (DW_OP_reg0)
    00000549 00000315 0000031c (DW_OP_fbreg: 4)

    000005a2 000002f0 000002fe (DW_OP_fbreg: 8)
    000005a2 000002fe 0000031c (DW_OP_reg2)



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