Re: Contributing LLVM.org patches to gud.el

[Daniel Colascione]

On 02/11/2015 02:37 AM, David Kastrup wrote:
> Daniel Colascione <address@hidden> writes:
> 
>> On 02/10/2015 07:43 PM, Stephen J. Turnbull wrote:
>>> Eli Zaretskii writes:
>>>
>>>  > > Uh, there is a connection.  Because modern IDEs tend to have useful
>>>  > > program information when debugging instead of (optimized out).
>>>  > 
>>>  > Compile with -Og (which should be the default anyway), and you have
>>>  > that with GCC/GDB as well.
>>>
>>> Er, most programs I compile default to -O3 (I mean upstream does).  So
>>> you can't debug a production build even if you have symbols.  Arrgh
>>
>> What exactly are the DWARF deficiencies that prevent a debugger from
>> unwinding caller-saved registers to their original values? The
>> specification seems more than powerful enough for the task.
> 
> The issue mostly are values which are not present explicitly anywhere.
> If the compiler can deduce the value/effect of a variable, it does not
> need to store it anywhere.

DWARF's virtual machine contains instructions for regenerating these
values from extant values and for building them out of thin air. See
section 2.5 of the DWARF 4 specification. GCC could emit enough
information to rebuild lost values, but does not.

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