Re: [PATCH] Catch errors in value_get_print_value

Daniel Jacobowitz
2007-02-08T17:41:44Z

On Fri, Feb 02, 2007 at 09:51:39AM +1300, Nick Roberts wrote:
>
> Currently when common_val_print throws an error from install_new_value it gets
> caught in mi_execute_command and prints an MI error (^error,...) without
> cleaning up. This patch catches the error in value_get_print_value so that GDB
> can proceed normally. It could be adapted to output something like
> "<error_reading_variable>" but I think the empty string works better.

Could you explain why? I would be confused to see an empty value in
my locals window. That's separate from this bug though.

> ! TRY_CATCH (except, RETURN_MASK_ERROR)
> ! {
> ! common_val_print (value, stb, format_code[(int) format], 1, 0, 0);
> ! }
> !

val_print, called by common_val_print, already has code to catch this
error and prettyprint it. It doesn't work in this case, through
common_val_print, because of:

#2 0x0000000000445abd in memory_error (status=5, memaddr=4)
at /space/fsf/commit/src/gdb/corefile.c:229
#3 0x00000000004aac7f in value_fetch_lazy (val=0x9688c0)
at /space/fsf/commit/src/gdb/valops.c:549
#4 0x00000000004a2f2f in value_contents_all (value=0x9688c0)
at /space/fsf/commit/src/gdb/value.c:331
#5 0x00000000004b19a4 in common_val_print (val=0x9688c0,
stream=0x94a6b0, format=0, deref_ref=1, recurse=0,
pretty=Val_no_prettyprint)
at /space/fsf/commit/src/gdb/valprint.c:284

I tried handling the error in value_check_printable. That doesn't have
quite the results that I wanted, because if install_new_value is called
first it sets value = NULL instead of leaving the unfetchable value
there. That's what happens for a1.

That gave me an idea. The error only arises for b1 in your testcase,
where initial && !changeable and indeed we never use var->print_value
if !changeable. So avoiding common_val_print in that case avoids the
error.

So I checked this in instead. Let me know if it doesn't work for you.

--
Daniel Jacobowitz
CodeSourcery

2007-02-08 Daniel Jacobowitz <dan@codesourcery.com>

* varobj.c (install_new_value): Only call value_get_print_value
if changeable.

Index: varobj.c
===================================================================
RCS file: /cvs/src/src/gdb/varobj.c,v
retrieving revision 1.82
diff -u -p -r1.82 varobj.c
--- varobj.c 24 Jan 2007 19:54:13 -0000 1.82
+++ varobj.c 8 Feb 2007 17:38:36 -0000
@@ -953,7 +953,7 @@ install_new_value (struct varobj *var, s
/* If the type is changeable, compare the old and the new values.
If this is the initial assignment, we don't have any old value
to compare with. */
- if (initial)
+ if (initial && changeable)
var->print_value = value_get_print_value (value, var->format);
else if (changeable)
{