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Re: RFA: Fix tracepoints for LOC_COMPUTED - sort of


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
 };


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