Re: RFA: Fix tracepoints for LOC_COMPUTED - sort of

[Jim Blandy <jimb at redhat dot com>]

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
>  };