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Re: [patch] Fix DW_OP_call2 and DW_OP_call4 for max-cache-age 0
- From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- To: Doug Evans <dje at google dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Thu, 2 Sep 2010 18:02:16 +0200
- Subject: Re: [patch] Fix DW_OP_call2 and DW_OP_call4 for max-cache-age 0
- References: <20100823185008.GA2926@host1.dyn.jankratochvil.net> <AANLkTimhw307GT1dxA5LFBnCA1njK1vk4+Sk8oamafkX@mail.gmail.com>
On Mon, 23 Aug 2010 21:30:06 +0200, Doug Evans wrote:
> On Mon, Aug 23, 2010 at 11:50 AM, Jan Kratochvil <jan.kratochvil@redhat.com> wrote:
> > as discussed on #gdb when you set max-cache-age 0 DW_OP_call{2,4} crashed GDB.
[...]
> > --- a/gdb/dwarf2read.c
> > +++ b/gdb/dwarf2read.c
> > @@ -1636,6 +1636,11 @@ dw2_do_instantiate_symtab (struct objfile *objfile,
> > Â{
> > Â struct cleanup *back_to;
> >
> > + Â/* Age the cache, releasing compilation units that have not been used
> > + Â Â recently. ÂAge them first so that we do not age out the requested PER_CU
> > + Â Â unit if DWARF2_MAX_CACHE_AGE is too low. Â*/
> > + Âage_cached_comp_units ();
>
> Aging cached units first feels weird (if not wrong at least weird); we
> may toss out something we're about to want.
> At the least IWBN to elaborate on why this fixes things.
As otherwise we will age out what we have found (on max-cache-age 0).
One could forbid value zero for max-cache-age but that also does not seem
right to me.
There is such a general cleanup moment when GDB is fully idle
- prepare_execute_command() - shouldn't age_cached_comp_units be called there?
But that way sooner or later we will age out every CU. This may occur a bit
even nowadays, the default value 5 is also very low. max-cache-age as "how
long" is IMO not userful to the user. There could be more a setting "how
many" CUs can be loaded at once. CU age would be then just an internal
indicator to maintain the count under the "how many" limit.
I would change "max-cache-age" to "max-cache-size" and call it from
prepare_execute_command() instead. I will provide a patch if not replied.
Thanks,
Jan