Re: [PATCH][gdb/testsuite] Fix gdb.ada/literals.exp with aarch64

[Joel Brobecker via Gdb-patches <gdb-patches@sourceware.org>]

> > Thanks for the patch.
> > 
> > My question is whether it actually makes sense that -1 be
> > a valid output for the print command above. I tried the addition
> > of ...
> > 
> >      | /* Note: Interprets ULLONG_MAX as -1.  */
> >      | yylval.typed_val.type = type_long_long (par_state);
> > 
> > ... to a patch of yours:
> > 
> >      | commit ac3afe36d73c84096685fece885d70b28bc9629f
> >      | Author: Tom de Vries <tdevries@suse.de>
> >      | Date:   Sat Jun 4 13:17:33 2022 +0200
> >      | Subject: [gdb/ada] Fix literal truncation
> >      |
> >      | Make sure we error out on overflow instead of truncating in all cases.
> >      |
> >      | Tested on x86_64-linux, with a build with --enable-targets=all.
> > 
> > Do you remember why we do this? Intuitively, you'd expect that GDB
> > would behave the same regardless of whether it selects type "long"
> > or "long long" for its processing, as long as both types are 64-bit.
> > 
> 
> I have no idea.  AFAICT it's been in gdb since the "Add base ada language
> files" commit from 2002 that we avoid "unsigned long long".
> 
> I've taken care to preserve the behaviour in the commit you refer to (and
> this patch), since I don't have the knowledge to decide that things should
> be different.
> 
> > With the above, we can take this patch as an intermediate remedy,
> > but I think we might need to dig deeper into why we use a signed
> > type in the case of long long but not long, particularly when both
> > types are the same size.
> > 
> > WDYT?
> > 
> 
> I'd be happy to write a patch to change the behaviour of gdb.  But somebody
> knowledgeable in Ada needs to specify what that needs to be.

We're really outside of the Ada language. Would you mind checking
what the C language does? I think it would make sense to do the same,
here. E.g., on x86_64-linux, I get:

    (gdb) p 0xffffffffffffffff
    $1 = 18446744073709551615

What do you think, TomT?

> > >   gdb/testsuite/gdb.ada/literals.exp | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/gdb/testsuite/gdb.ada/literals.exp b/gdb/testsuite/gdb.ada/literals.exp
> > > index a6ac89b540f..744a6bc573c 100644
> > > --- a/gdb/testsuite/gdb.ada/literals.exp
> > > +++ b/gdb/testsuite/gdb.ada/literals.exp
> > > @@ -36,4 +36,4 @@ gdb_test "print 16#f#e1" " = 240"
> > >   gdb_test "print 16#1#e10" " = 1099511627776"
> > >   gdb_test "print/x 16#7fffffffffffffff#" " = 0x7fffffffffffffff"
> > > -gdb_test "print 16#ffffffffffffffff#" " = -1"
> > > +gdb_test "print 16#ffffffffffffffff#" " = (-1|18446744073709551615)"
> > 

-- 
Joel