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

[Tom de Vries via Gdb-patches <gdb-patches@sourceware.org>]

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On 7/28/22 15:10, Joel Brobecker wrote:
>>> 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
> 

Ack, that's what the C language does.

This patch changes gdb to print 18446744073709551615 for ada as well.

So, pick your favorite patch ;)

Thanks,
- Tom

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

On aarch64-linux, I run into:
...
(gdb) print 16#ffffffffffffffff#^M
$7 = 18446744073709551615^M
(gdb) FAIL: gdb.ada/literals.exp: print 16#ffffffffffffffff#
...
while on x86_64-linux instead, I get:
...
(gdb) print 16#ffffffffffffffff#^M
$7 = -1^M
(gdb) PASS: gdb.ada/literals.exp: print 16#ffffffffffffffff#
...

We can easily reproduce this on x86_64-linux using:
...
$ gdb -q -batch -ex "set lang ada" -ex "set arch i386" \
  -ex "print 16#ffffffffffffffff#"
$1 = -1
$ gdb -q -batch -ex "set lang ada" -ex "set arch aarch64" \
  -ex "print 16#ffffffffffffffff#"
$1 = 18446744073709551615
...

With i386, we have:
...
(gdb) p int_bits
$3 = 32
(gdb) p long_bits
$4 = 32
(gdb) p long_long_bits
$5 = 64
...
and so in processInt we hit the fits-in-unsigned-long-long case where we use
as type long long:
...
      /* Note: Interprets ULLONG_MAX as -1.  */
      yylval.typed_val.type = type_long_long (par_state);
...

With aarch64, we have instead:
...
(gdb) p int_bits
$1 = 32
(gdb) p long_bits
$2 = 64
(gdb) p long_long_bits
$3 = 64
...
and so in processInt we hit the fits-in-unsigned-long case where we use
as type unsigned long:
...
      yylval.typed_val.type
        = builtin_type (par_state->gdbarch ())->builtin_unsigned_long;
...

It's not clear why for ada we're using long long for the
fits-in-unsigned-long-long case.

Fix this by using unsigned long long for the fits-in-unsigned-long-long case,
meaning the new reference output is 18446744073709551615 instead of -1.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29416

---
 gdb/ada-lex.l                      | 4 ++--
 gdb/testsuite/gdb.ada/literals.exp | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/gdb/ada-lex.l b/gdb/ada-lex.l
index 002eb811e41..ed88d502e9f 100644
--- a/gdb/ada-lex.l
+++ b/gdb/ada-lex.l
@@ -498,8 +498,8 @@ processInt (struct parser_state *par_state, const char *base0,
     yylval.typed_val.type = type_long_long (par_state);
   else if (fits_in_type (1, value, long_long_bits, false))
     {
-      /* Note: Interprets ULLONG_MAX as -1.  */
-      yylval.typed_val.type = type_long_long (par_state);
+      yylval.typed_val.type
+	= builtin_type (par_state->gdbarch ())->builtin_unsigned_long_long;
       /* See unsigned long case above.  */
       if (value & LONGEST_SIGN)
 	yylval.typed_val.val =
diff --git a/gdb/testsuite/gdb.ada/literals.exp b/gdb/testsuite/gdb.ada/literals.exp
index a6ac89b540f..6badc857292 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#" " = 18446744073709551615"