collecting optimized out variables regression (Re: RFA: rewrite dwarf->ax translator (Was: RFC: implement DW_OP_bit_piece))

[Pedro Alves <pedro@codesourcery.com>]

Hi Tom,

After the rewrite, I'm seeing this:

 (gdb) p m
 $1 = <value optimized out>
 (gdb) maint agent m
  ../../src/gdb/utils.c:1363: internal-error: virtual memory exhausted: can't allocate 562945039736192 bytes.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n) 


#0  internal_error (file=0x7531ac "../../src/gdb/utils.c", line=1363, 
    string=0x753568 "virtual memory exhausted: can't allocate %ld bytes.") at ../../src/gdb/utils.c:1162
#1  0x0000000000417464 in nomem (size=562949953380224) at ../../src/gdb/utils.c:1363
#2  0x00000000004174c3 in xmalloc (size=562949953380224) at ../../src/gdb/utils.c:1394
#3  0x00000000005b1ac7 in compile_dwarf_to_ax (expr=0xebd020, loc=0x7fffffffd9b0, arch=0xcc9a20, addr_size=8, 
    op_ptr=0x0, op_end=0x7fffffffd7e0 " \320\353", per_cu=0xcada90) at ../../src/gdb/dwarf2loc.c:1220
#4  0x00000000005b4b78 in loclist_tracepoint_var_ref (symbol=0xd22c30, gdbarch=0xcc9a20, ax=0xebd020, 
    value=0x7fffffffd9b0) at ../../src/gdb/dwarf2loc.c:2572
#5  0x000000000048be46 in gen_var_ref (gdbarch=0xcc9a20, ax=0xebd020, value=0x7fffffffd9b0, var=0xd22c30)
    at ../../src/gdb/ax-gdb.c:713
#6  0x000000000048e570 in gen_expr (exp=0xed5280, pc=0x7fffffffd9c8, ax=0xebd020, value=0x7fffffffd9b0)
    at ../../src/gdb/ax-gdb.c:1962
#7  0x000000000048f92a in gen_trace_for_expr (scope=4197499, expr=0xed5280) at ../../src/gdb/ax-gdb.c:2387
#8  0x000000000048fabc in agent_command (exp=0xb4821c "m", from_tty=1) at ../../src/gdb/ax-gdb.c:2456

The xmalloc in question is this:

 offsets = xmalloc ((op_end - op_ptr) * sizeof (int));

`op_end' and `op_ptr' are `data' and `data + size' in loclist_tracepoint_var_ref:

  data = find_location_expression (dlbaton, &size, ax->scope);

  compile_dwarf_to_ax (ax, value, gdbarch, addr_size, data, data + size,
		       dlbaton->per_cu);

where:

 (top-gdb) p data
 $1 = (const gdb_byte *) 0x0
 (top-gdb) p size
 $2 = 140737488345056
 (top-gdb) p /x 
 $3 = 0x7fffffffd7e0

whoops.

On Thursday 03 June 2010 21:12:13, Tom Tromey wrote:

> 	(dwarf2_tracepoint_var_ref): Likewise.
> 	(locexpr_tracepoint_var_ref): Use compile_dwarf_to_ax.
> 	(loclist_tracepoint_var_ref): Likewise.

> -static void
> -dwarf2_tracepoint_var_ref (struct symbol *symbol, struct gdbarch *gdbarch,
> -			   struct agent_expr *ax, struct axs_value *value,
> -			   const gdb_byte *data, int size)
> -{
(...)
> -      
> -  if (!data || size == 0)
> -    {
> -      value->optimized_out = 1;
> -      return;
> -    }

Apparently, this bit was lost with the rewrite.

(...)

> @@ -1813,9 +2269,10 @@ locexpr_tracepoint_var_ref (struct symbol *symbol, struct gdbarch *gdbarch,
>  			    struct agent_expr *ax, struct axs_value *value)
>  {
>    struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
> +  unsigned int addr_size = dwarf2_per_cu_addr_size (dlbaton->per_cu);
>  
> -  dwarf2_tracepoint_var_ref (symbol, gdbarch, ax, value,
> -			     dlbaton->data, dlbaton->size);
> +  compile_dwarf_to_ax (ax, value, gdbarch, addr_size,
> +		       dlbaton->data, dlbaton->data + dlbaton->size);
>  }
>  
>  /* The set of location functions used with the DWARF-2 expression
> @@ -1957,10 +2414,11 @@ loclist_tracepoint_var_ref (struct symbol *symbol, struct gdbarch *gdbarch,
>    struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
>    const gdb_byte *data;
>    size_t size;
> +  unsigned int addr_size = dwarf2_per_cu_addr_size (dlbaton->per_cu);
>  
>    data = find_location_expression (dlbaton, &size, ax->scope);
>  
> -  dwarf2_tracepoint_var_ref (symbol, gdbarch, ax, value, data, size);
> +  compile_dwarf_to_ax (ax, value, gdbarch, addr_size, data, data + size);
>  }

This patch fixes it for me.  Is this the correct approach, or maybe there
was intent to handle this differently?

-- 
Pedro Alves

2010-07-01  Pedro Alves  <pedro@codesourcery.com>

	* dwarf2loc.c (locexpr_tracepoint_var_ref)
	(loclist_tracepoint_var_ref): Handle optimized out values.

---
 gdb/dwarf2loc.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

Index: src/gdb/dwarf2loc.c
===================================================================
--- src.orig/gdb/dwarf2loc.c	2010-07-01 12:19:35.000000000 +0100
+++ src/gdb/dwarf2loc.c	2010-07-01 13:32:38.000000000 +0100
@@ -2416,9 +2416,12 @@ locexpr_tracepoint_var_ref (struct symbo
   struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
   unsigned int addr_size = dwarf2_per_cu_addr_size (dlbaton->per_cu);
 
-  compile_dwarf_to_ax (ax, value, gdbarch, addr_size,
-		       dlbaton->data, dlbaton->data + dlbaton->size,
-		       dlbaton->per_cu);
+  if (dlbaton->data == NULL || dlbaton->size == 0)
+    value->optimized_out = 1;
+  else
+    compile_dwarf_to_ax (ax, value, gdbarch, addr_size,
+			 dlbaton->data, dlbaton->data + dlbaton->size,
+			 dlbaton->per_cu);
 }
 
 /* The set of location functions used with the DWARF-2 expression
@@ -2568,9 +2571,11 @@ loclist_tracepoint_var_ref (struct symbo
   unsigned int addr_size = dwarf2_per_cu_addr_size (dlbaton->per_cu);
 
   data = find_location_expression (dlbaton, &size, ax->scope);
-
-  compile_dwarf_to_ax (ax, value, gdbarch, addr_size, data, data + size,
-		       dlbaton->per_cu);
+  if (data == NULL || size == 0)
+    value->optimized_out = 1;
+  else
+    compile_dwarf_to_ax (ax, value, gdbarch, addr_size, data, data + size,
+			 dlbaton->per_cu);
 }
 
 /* The set of location functions used with the DWARF-2 expression