From: "Rohr, Stephan" <stephan.rohr@intel.com>
To: "gdb-patches@sourceware.org" <gdb-patches@sourceware.org>
Cc: "tom@tromey.com" <tom@tromey.com>
Subject: RE: [PATCH 1/1] gdb/dwarf2: Fix 'rw_pieced_value' for values casted to different type.
Date: Fri, 19 Aug 2022 07:41:51 +0000 [thread overview]
Message-ID: <DM6PR11MB456410F376063F7C8CDE9729936C9@DM6PR11MB4564.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20220422144420.3545190-2-stephan.rohr@intel.com>
Hi All,
I would like to ask for review of my patch.
BR
stephan
> -----Original Message-----
> From: Rohr, Stephan <stephan.rohr@intel.com>
> Sent: Friday, April 22, 2022 4:44 PM
> To: gdb-patches@sourceware.org
> Cc: Rohr, Stephan <stephan.rohr@intel.com>; tom@tromey.com
> Subject: [PATCH 1/1] gdb/dwarf2: Fix 'rw_pieced_value' for values casted to
> different type.
>
> From: "Rohr, Stephan" <stephan.rohr@intel.com>
>
> The 'rw_pieced_value' function is executed when fetching a (lazy) variable
> described by 'DW_OP_piece' or 'DW_OP_bit_piece'. The function checks the
> 'type' and 'enclosing_type' fields of the value for identity.
>
> * The 'type' field describes the type of a value.
> * In most cases, the 'enclosing_type' field is identical to the
> 'type' field.
> * Scenarios where the 'type' and 'enclosing_type' of an object
> differ are described in 'gdb/value.c'. Possible cases are:
> * If a value represents a C++ object, then the 'type' field
> gives the object's compile-time type. If the object actually
> belongs to some class derived from `type', perhaps with other
> base classes and additional members, then `type' is just a
> subobject of the real thing, and the full object is probably
> larger than `type' would suggest.
> * If 'type' is a dynamic class (i.e. one with a vtable), then GDB
> can actually determine the object's run-time type by looking at
> the run-time type information in the vtable. GDB may then elect
> to read the entire object.
> * If the user casts a variable to a different type
> (e.g. 'print (<type> []) <variable>'), the value's type is
> updated before reading the value.
>
> If a lazy value is fetched, GDB allocates space based on the enclosing type's
> length and typically reads the 'full' object.
> This is not implemented for pieced values and causes an internal error if
> 'type' and 'enclosing_type' of a value are not identical.
>
> However, GDB can read the value based on its type. Thus, it should be
> sufficient to check if the type's length (potentially shifted by
> 'embedded_offset') does not exceed the enclosing type's length which was
> used for memory allocation.
> ---
> gdb/dwarf2/expr.c | 6 ++----
> gdb/testsuite/gdb.dwarf2/shortpiece.exp | 12 ++++++++++++
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c index
> 99862583336..6330a5787fc 100644
> --- a/gdb/dwarf2/expr.c
> +++ b/gdb/dwarf2/expr.c
> @@ -174,10 +174,8 @@ rw_pieced_value (value *v, value *from, bool
> check_optimized)
> }
> else
> {
> - if (value_type (v) != value_enclosing_type (v))
> - internal_error (__FILE__, __LINE__,
> - _("Should not be able to create a lazy value with "
> - "an enclosing type"));
> + gdb_assert ((TYPE_LENGTH (value_type (v)) + value_embedded_offset
> (v))
> + <= TYPE_LENGTH (value_enclosing_type (v)));
> if (check_optimized)
> v_contents = nullptr;
> else
> diff --git a/gdb/testsuite/gdb.dwarf2/shortpiece.exp
> b/gdb/testsuite/gdb.dwarf2/shortpiece.exp
> index f5a933e521b..19cdec83193 100644
> --- a/gdb/testsuite/gdb.dwarf2/shortpiece.exp
> +++ b/gdb/testsuite/gdb.dwarf2/shortpiece.exp
> @@ -98,3 +98,15 @@ if { [prepare_for_testing "failed to prepare" ${testfile}
> \ gdb_test "p s1" " = {a = 1, b = 0}"
> gdb_test "p s2" \
> "access outside bounds of object referenced via synthetic pointer"
> +
> +# When fetching a lazy value, GDB typically tries to fetch the 'full'
> +# object based on the enclosing type. GDB does not support the reading
> +# of a pieced value with a (possibly larger) enclosing type. However,
> +# the user may want to print a value casted to a different type, # e.g.
> +print (<type> []) <variable>. This cast causes an update of the #
> +value's type. In case of a pieced value, GDB failed to fetch the #
> +value's content.
> +# This test verifies that GDB can print a pieced value casted to a #
> +different type.
> +gdb_test "p (int \[\]) s1" " = \\{1\\, 0\\}"
> +gdb_test "p (short \[\]) s1" " = \\{1\\, 0\\, 0\\, <synthetic pointer>\\}"
> --
> 2.25.1
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
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next prev parent reply other threads:[~2022-08-19 7:42 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-22 14:44 [PATCH 0/1] " Stephan Rohr
2022-04-22 14:44 ` [PATCH 1/1] gdb/dwarf2: " Stephan Rohr
2022-06-06 16:51 ` Bruno Larsen
2022-07-14 7:50 ` Rohr, Stephan
2022-07-21 12:21 ` Rohr, Stephan
2022-08-02 6:30 ` Rohr, Stephan
2022-08-11 7:09 ` Rohr, Stephan
2022-08-19 7:41 ` Rohr, Stephan [this message]
2022-08-19 16:39 ` Simon Marchi
2022-10-11 8:03 ` Rohr, Stephan
2022-10-21 17:06 ` Tom Tromey
2022-10-14 18:28 ` Tom Tromey
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