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Re: GCC 4.1.0 doesn't generate DWARF 2 output for function arguments?

On Wed, Apr 05, 2006 at 06:25:58PM +1200, Nick Roberts wrote:
>  > > It also causes GDB to generate errors on the output of other commands:
>  > > 
>  > >   (gdb) info locals
>  > >   argc = Cannot access memory at address 0x0
>  > > 
>  > > as well as the GDB/MI equivalent -stack-list-locals.  This breaks the
>  > > front end that I'm writing fo Emacs.
>  > 
>  > That's a bug in GDB, and not hard to fix.  You're welcome to do it, or
>  > to file it in GNATS :-)
> Is it easy?  With the optimisation GDB thinks argc is LOC_STATIC, which is why
> it tries to print its value with the "info locals" command, even though it is
> not a local variable in GDB's usual sense.

Well, there are at least three bugs here.  First, it should be printed
in "info args" instead of "info locals".  Secondly, failure to access
it should not be fatal.  Third, it's not really LOC_STATIC.

The third is the easiest to fix.  I assume the reason that it is
assigned LOC_STATIC is in new_symbol, where we check for
DW_AT_external?  In that branch, if there is no external flag, we could
change the LOC_STATIC to LOC_OPTIMIZED_OUT. That should get you an
<optimized out> instead of an error at address 0x0.

Fixing "info args" would be a matter of either adding yet another LOC_
value, which I don't think is a good idea, or moving the
is-this-an-argument check out of the LOC_* value.  Having both
LOC_COMPUTED and LOC_COMPUTED_ARG has always been a bit of a hack.
There could be a flag somewhere instead.  But, this would require
changing a bunch of switch statements in various places.

And for the fatal access, it might be possible to add an appropriate
check in value_check_printable to print something like <invalid
address> (already used by the C++ code).  That would fix both the CLI
command and the MI command.

>  The only way I can think of doing
> thi is testing if sym-> is "argc" or "argv" in the LOC_STATIC case of
> the switch statements of print_block_frame_locals and list_args_or_locals.
> Its inelegant and probably not general either.

Heck no!  This has nothing to do with argc or argv, and everything to
do with unused arguments.

Daniel Jacobowitz

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