From: Andrew Burgess <aburgess@redhat.com>
To: Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>,
gdb-patches@sourceware.org
Cc: Simon Marchi <simon.marchi@efficios.com>
Subject: Re: [PATCH 1/2] gdb/testsuite: add test for negative subrange bounds with unsigned form
Date: Fri, 20 Jan 2023 12:51:43 +0000 [thread overview]
Message-ID: <87ilh1e5cw.fsf@redhat.com> (raw)
In-Reply-To: <20230120050824.306976-1-simon.marchi@efficios.com>
Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:
> I am looking at this code [1]:
>
> /* Normally, the DWARF producers are expected to use a signed
> constant form (Eg. DW_FORM_sdata) to express negative bounds.
> But this is unfortunately not always the case, as witnessed
> with GCC, for instance, where the ambiguous DW_FORM_dataN form
> is used instead. To work around that ambiguity, we treat
> the bounds as signed, and thus sign-extend their values, when
> the base type is signed. */
> negative_mask =
> -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1));
> if (low.kind () == PROP_CONST
> && !base_type->is_unsigned () && (low.const_val () & negative_mask))
> low.set_const_val (low.const_val () | negative_mask);
> if (high.kind () == PROP_CONST
> && !base_type->is_unsigned () && (high.const_val () & negative_mask))
> high.set_const_val (high.const_val () | negative_mask);
>
> Nothing in the testsuite seems to exercise it, as when I remove it, all
> of gdb.dwarf2 still passes. And tests in other directories would be
> compiler-dependent, so would rely on having a buggy compiler.
>
> Update gdb.dwarf2/subrange.exp to have a test for it. When removing the
> code above, the new test fails with:
>
> ptype array_with_buggy_negative_bounds_type^M
> type = array [240..244] of signed_byte^M
> (gdb) FAIL: gdb.dwarf2/subrange.exp: ptype array_with_buggy_negative_bounds_type
>
> instead of the expected:
>
> ptype array_with_buggy_negative_bounds_type^M
> type = array [-16..-12] of signed_byte^M
> (gdb) PASS: gdb.dwarf2/subrange.exp: ptype array_with_buggy_negative_bounds_type
>
> [1] https://gitlab.com/gnutools/binutils-gdb/-/blob/5ea14aa4e53fa37f4ba4517497ed2c1e4c60dee2/gdb/dwarf2/read.c#L17681-17695
>
> Change-Id: I1992a3ff0cb1e90fa8a9114dae6c591792f059c2
> ---
> gdb/testsuite/gdb.dwarf2/subrange.exp | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/gdb/testsuite/gdb.dwarf2/subrange.exp b/gdb/testsuite/gdb.dwarf2/subrange.exp
> index 72d7babc88e..8a8443f31a8 100644
> --- a/gdb/testsuite/gdb.dwarf2/subrange.exp
> +++ b/gdb/testsuite/gdb.dwarf2/subrange.exp
> @@ -28,6 +28,7 @@ Dwarf::assemble $asm_file {
> compile_unit {{language @DW_LANG_Pascal83}} {
> declare_labels byte_label typedef_label array_label
>
> + # A subrange's underlying type that is a typedef.
> byte_label: base_type {
> {name byte}
> {encoding @DW_ATE_unsigned}
> @@ -54,6 +55,28 @@ Dwarf::assemble $asm_file {
> {name TByteArray}
> {type :$array_label}
> }
> +
> + # This subrange's underlying type is signed, but the bounds are
> + # specified using a non-signed form.
> + declare_labels signed_byte_label subrange_with_buggy_negative_bounds_label
> +
> + signed_byte_label: base_type {
> + {name signed_byte}
> + {encoding @DW_ATE_signed}
> + {byte_size 1 DW_FORM_sdata}
> + }
> +
> + # The bounds mean -16 to -12.
> + subrange_with_buggy_negative_bounds_label: subrange_type {
> + {lower_bound 0xf0 DW_FORM_udata}
> + {upper_bound 0xf4 DW_FORM_udata}
> + {type :$signed_byte_label}
> + }
> +
> + DW_TAG_variable {
> + {name subrange_with_buggy_negative_bounds_variable}
> + {type :$subrange_with_buggy_negative_bounds_label}
> + }
> }
> }
> }
> @@ -67,3 +90,5 @@ gdb_test_no_output "set language pascal"
>
> gdb_test "ptype TByteArray" \
> "type = array \\\[0\\.\\.191\\\] of byte"
> +gdb_test "ptype subrange_with_buggy_negative_bounds_variable" \
> + "type = -16..-12"
Should be "type = -16\\.\\.-12"
Otherwise, looks good.
Thanks,
Andrew
> --
> 2.39.1
next prev parent reply other threads:[~2023-01-20 12:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-20 5:08 Simon Marchi
2023-01-20 5:08 ` [PATCH 2/2] gdb/dwarf: fix UBsan crash in read_subrange_type Simon Marchi
2023-01-20 13:03 ` Andrew Burgess
2023-01-20 16:51 ` Simon Marchi
2023-01-20 12:51 ` Andrew Burgess [this message]
2023-01-20 16:38 ` [PATCH 1/2] gdb/testsuite: add test for negative subrange bounds with unsigned form Simon Marchi
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