Re: Ping! [PATCH]: Tracking and reporting uninitialized variables

[Jim Blandy <jimb@codesourcery.com>]

Caroline Tice <ctice@apple.com> writes:
>> As part of some work I have been doing on improving debugging of
>> optimized code, I
>> have created a GCC patch that tags variables it believes are
>> uninitialized with a new
>> Dwarf op (an extension), DW_OP_GNU_uninit.   I have submitted that
>> patch to the
>> GCC patches list and am waiting for approval to commit it.   I have
>> also created the
>> following gdb patch to recognize the new op and inform the user when
>> a variable
>> the user requests to see is uninitialized.
>>
>> I have tested this patch on some small testcases and I have run the
>> gdb dejagnu
>> testsuite with no regressions.  I am new to submitting things to
>> this list, so if there
>> is anything else I ought to have done, please let me know
>> (kindly!).

Hi, Caroline.  This seems like a nice patch.

In a multi-piece location expression, can each piece be individually
initialized or uninitialized?  If that's so, then there should also be
an 'initialized' member of 'struct dwarf_expr_piece', which gets set
appropriately for each piece in a multi-piece location expression.

Either way, the code for DW_OP_GNU_uninit should check that it's the
last opcode in the piece or in the entire expression, as the
DW_OP_reg* cases do.

I think the 'struct dwarf_expr_context' member should be named
simply 'initialized', instead of 'var_status'.  The 'struct value'
field should be named 'initialized', and the accessor functions should
be named 'value_initialized' and 'set_value_initialized'.  The comment
in value.h actually needs to be filled in; the description should be
thorough enough to allow someone who otherwise knows how GDB works to
use those functions, without reading their definitions.

I couldn't see from your patch why 'signed_address_type',
'unsigned_address_type', and 'add_piece' were made visible outside
dwarf2expr.c; that should be left out of the patch if it's not needed.

Have you filed a copyright assignment with the FSF?