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Re: RFA: Fix tracepoints for LOC_COMPUTED - sort of


Thanks, checked in (with a warning I accidentally introduced fixed).

On Fri, Feb 28, 2003 at 02:45:29PM -0500, Jim Blandy wrote:
> 
> Looks good to me!
> 
> Daniel Jacobowitz <drow at mvista dot com> writes:
> 
> > On Mon, Feb 24, 2003 at 04:50:27PM -0500, Jim Blandy wrote:
> > > 
> > > Daniel Jacobowitz <drow at mvista dot com> writes:
> > > > Like the description function, this is pretty minimal; I don't have time to
> > > > write a full evaluator right now, and I don't have access to a tracepoint
> > > > stub, so I suggest someone who does implement this properly.  For now,
> > > > though, this handles the most likely types: DW_OP_reg and DW_OP_fbreg.  It's
> > > > enough to fix the test failures; it's correct as far as it goes; and it
> > > > properly raises an error if it gets confused.
> > > > 
> > > > Is this OK?  Should I file a PR about the need for a proper
> > > > evaluator?
> > > 
> > > Well, the problem is likely to sit around indefinitely:
> > > 1) I don't think anyone's using tracepoints at the moment.
> > > 2) Compiling Dwarf 2 bytecodes into ax bytecodes is, in general, not
> > >    a simple thing at all.
> > > 
> > > So its importance and difficulty both work against it.  Would a
> > > comment be better in this sort of situation?  I don't know.
> > 
> > I went for a comment, because I'm a comment sort of person.
> > 
> > > You know, dwarf2read.c's read_{un,}signed_leb128 don't actually need
> > > their BFD argument for anything.  The call to bfd_get_8 ignores it;
> > > it's just a char fetch anyway.  In the future, I wonder if we could
> > > just use those everywhere.
> > 
> > Probably.  There's a set in dwarf2cfi.c too; it would be nice to cut
> > them down.
> > 
> > > Gotta have a better error message, dude.  It only takes a few
> > > seconsd.  Think of the poor user.
> > 
> > > You should check that that's actually the end of the expression, too.
> > 
> > OK, even I am kind of ashamed of the error messages in the last
> > version... thanks for keeping me honest.  How's this?
> > 
> > -- 
> > Daniel Jacobowitz
> > MontaVista Software                         Debian GNU/Linux Developer
> > 
> > 2003-02-26  Daniel Jacobowitz  <drow at mvista dot com>
> > 
> > 	* Makefile.in (dwarf2loc.o): Update dependencies.
> > 	* ax-gdb.c (gen_var_ref): Handle LOC_COMPUTED and LOC_COMPUTED_ARG.
> > 	* dwarf2expr.c (read_uleb128, read_sleb128): Make non-static.
> > 	* dwarf2expr.h (read_uleb128, read_sleb128): Add prototypes.
> > 	* dwarf2loc.c: Include "ax.h" and "ax-gdb.h".
> > 	(locexpr_tracepoint_var_ref): New function.
> > 	(dwarf2_locexpr_funcs): Add locexpr_tracepoint_var_ref.
> > 
> > Index: Makefile.in
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/Makefile.in,v
> > retrieving revision 1.335
> > diff -u -p -r1.335 Makefile.in
> > --- Makefile.in	21 Feb 2003 15:24:17 -0000	1.335
> > +++ Makefile.in	26 Feb 2003 21:30:44 -0000
> > @@ -1639,7 +1639,7 @@ dwarf2expr.o: dwarf2expr.c $(defs_h) $(s
> >  	 $(gdbcore_h) $(dwarf2expr_h)
> >  dwarf2loc.o: dwarf2loc.c $(defs_h) $(ui_out_h) $(value_h) $(frame_h) \
> >  	$(gdbcore_h) $(target_h) $(inferior_h) $(dwarf2expr_h) \
> > -	$(dwarf2loc_h) $(gdb_string_h)
> > +	$(dwarf2loc_h) $(ax_h) $(ax_gdb_h) $(gdb_string_h)
> >  dwarf2read.o: dwarf2read.c $(defs_h) $(bfd_h) $(symtab_h) $(gdbtypes_h) \
> >  	$(symfile_h) $(objfiles_h) $(elf_dwarf2_h) $(buildsym_h) \
> >  	$(demangle_h) $(expression_h) $(filenames_h) $(macrotab_h) \
> > Index: ax-gdb.c
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/ax-gdb.c,v
> > retrieving revision 1.20
> > diff -u -p -r1.20 ax-gdb.c
> > --- ax-gdb.c	25 Feb 2003 21:36:16 -0000	1.20
> > +++ ax-gdb.c	26 Feb 2003 21:30:44 -0000
> > @@ -618,6 +618,11 @@ gen_var_ref (struct agent_expr *ax, stru
> >        }
> >        break;
> >  
> > +    case LOC_COMPUTED:
> > +    case LOC_COMPUTED_ARG:
> > +      (*SYMBOL_LOCATION_FUNCS (var)->tracepoint_var_ref) (var, ax, value);
> > +      break;
> > +
> >      case LOC_OPTIMIZED_OUT:
> >        error ("The variable `%s' has been optimized out.",
> >  	     SYMBOL_PRINT_NAME (var));
> > Index: dwarf2expr.c
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/dwarf2expr.c,v
> > retrieving revision 1.1
> > diff -u -p -r1.1 dwarf2expr.c
> > --- dwarf2expr.c	21 Feb 2003 15:24:17 -0000	1.1
> > +++ dwarf2expr.c	26 Feb 2003 21:30:44 -0000
> > @@ -115,7 +115,7 @@ dwarf_expr_eval (struct dwarf_expr_conte
> >     by R, and return the new value of BUF.  Verify that it doesn't extend
> >     past BUF_END.  */
> >  
> > -static unsigned char *
> > +unsigned char *
> >  read_uleb128 (unsigned char *buf, unsigned char *buf_end, ULONGEST * r)
> >  {
> >    unsigned shift = 0;
> > @@ -141,7 +141,7 @@ read_uleb128 (unsigned char *buf, unsign
> >     by R, and return the new value of BUF.  Verify that it doesn't extend
> >     past BUF_END.  */
> >  
> > -static unsigned char *
> > +unsigned char *
> >  read_sleb128 (unsigned char *buf, unsigned char *buf_end, LONGEST * r)
> >  {
> >    unsigned shift = 0;
> > Index: dwarf2expr.h
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/dwarf2expr.h,v
> > retrieving revision 1.1
> > diff -u -p -r1.1 dwarf2expr.h
> > --- dwarf2expr.h	21 Feb 2003 15:24:17 -0000	1.1
> > +++ dwarf2expr.h	26 Feb 2003 21:30:44 -0000
> > @@ -94,4 +94,10 @@ void dwarf_expr_eval (struct dwarf_expr_
> >  		      size_t len);
> >  CORE_ADDR dwarf_expr_fetch (struct dwarf_expr_context *ctx, int n);
> >  
> > +
> > +unsigned char *read_uleb128 (unsigned char *buf, unsigned char *buf_end,
> > +			     ULONGEST * r);
> > +unsigned char *read_sleb128 (unsigned char *buf, unsigned char *buf_end,
> > +			     LONGEST * r);
> > +
> >  #endif
> > Index: dwarf2loc.c
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/dwarf2loc.c,v
> > retrieving revision 1.1
> > diff -u -p -r1.1 dwarf2loc.c
> > --- dwarf2loc.c	21 Feb 2003 15:24:17 -0000	1.1
> > +++ dwarf2loc.c	26 Feb 2003 21:30:44 -0000
> > @@ -26,6 +26,8 @@
> >  #include "gdbcore.h"
> >  #include "target.h"
> >  #include "inferior.h"
> > +#include "ax.h"
> > +#include "ax-gdb.h"
> >  
> >  #include "elf/dwarf2.h"
> >  #include "dwarf2expr.h"
> > @@ -277,11 +279,73 @@ locexpr_describe_location (struct symbol
> >    return 1;
> >  }
> >  
> > +
> > +/* Describe the location of SYMBOL as an agent value in VALUE, generating
> > +   any necessary bytecode in AX.
> > +
> > +   NOTE drow/2003-02-26: This function is extremely minimal, because
> > +   doing it correctly is extremely complicated and there is no
> > +   publicly available stub with tracepoint support for me to test
> > +   against.  When there is one this function should be revisited.  */
> > +
> > +void
> > +locexpr_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,
> > +			    struct axs_value * value)
> > +{
> > +  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
> > +
> > +  if (dlbaton->size == 0)
> > +    error ("Symbol \"%s\" has been optimized out.",
> > +	   SYMBOL_PRINT_NAME (symbol));
> > +
> > +  if (dlbaton->size == 1
> > +      && dlbaton->data[0] >= DW_OP_reg0
> > +      && dlbaton->data[0] <= DW_OP_reg31)
> > +    {
> > +      value->kind = axs_lvalue_register;
> > +      value->u.reg = dlbaton->data[0] - DW_OP_reg0;
> > +    }
> > +  else if (dlbaton->data[0] == DW_OP_regx)
> > +    {
> > +      ULONGEST reg;
> > +      read_uleb128 (dlbaton->data + 1, dlbaton->data + dlbaton->size,
> > +		    &reg);
> > +      value->kind = axs_lvalue_register;
> > +      value->u.reg = reg;
> > +    }
> > +  else if (dlbaton->data[0] == DW_OP_fbreg)
> > +    {
> > +      /* And this is worse than just minimal; we should honor the frame base
> > +	 as above.  */
> > +      int frame_reg;
> > +      LONGEST frame_offset;
> > +      char *buf_end;
> > +
> > +      buf_end = read_sleb128 (dlbaton->data + 1, dlbaton->data + dlbaton->size,
> > +			      &frame_offset);
> > +      if (buf_end != dlbaton->data + dlbaton->size)
> > +	error ("Unexpected opcode after DW_OP_fbreg for symbol \"%s\".",
> > +	       SYMBOL_PRINT_NAME (symbol));
> > +
> > +      TARGET_VIRTUAL_FRAME_POINTER (ax->scope, &frame_reg, &frame_offset);
> > +      ax_reg (ax, frame_reg);
> > +      ax_const_l (ax, frame_offset);
> > +      ax_simple (ax, aop_add);
> > +
> > +      ax_const_l (ax, frame_offset);
> > +      ax_simple (ax, aop_add);
> > +      value->kind = axs_lvalue_memory;
> > +    }
> > +  else
> > +    error ("Unsupported DWARF opcode in the location of \"%s\".",
> > +	   SYMBOL_PRINT_NAME (symbol));
> > +}
> > +
> >  /* The set of location functions used with the DWARF-2 expression
> >     evaluator.  */
> >  struct location_funcs dwarf2_locexpr_funcs = {
> >    locexpr_read_variable,
> >    locexpr_read_needs_frame,
> >    locexpr_describe_location,
> > -  NULL
> > +  locexpr_tracepoint_var_ref
> >  };
> 

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer


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